diff --git a/client/mcp_service.go b/client/mcp_service.go
index fa19978f..c76a1c97 100644
--- a/client/mcp_service.go
+++ b/client/mcp_service.go
@@ -35,11 +35,19 @@ type MCPService struct {
 	UpdatedAt      string             `json:"updated_at"`
 }
 
-// MCPAuthConfig represents authentication configuration for MCP service
+// MCPAuthConfig represents authentication configuration for MCP service.
+//
+// ClearAPIKey and ClearToken are write-only flags used in Update requests to
+// explicitly remove a stored credential. The server never returns these
+// fields in responses.
 type MCPAuthConfig struct {
 	APIKey        string            `json:"api_key,omitempty"`
 	Token         string            `json:"token,omitempty"`
 	CustomHeaders map[string]string `json:"custom_headers,omitempty"`
+
+	// Write-only clear flags.
+	ClearAPIKey bool `json:"clear_api_key,omitempty"`
+	ClearToken  bool `json:"clear_token,omitempty"`
 }
 
 // MCPAdvancedConfig represents advanced configuration for MCP service
diff --git a/frontend/src/api/mcp-service.ts b/frontend/src/api/mcp-service.ts
index 1aa7a2ee..2b969dda 100644
--- a/frontend/src/api/mcp-service.ts
+++ b/frontend/src/api/mcp-service.ts
@@ -13,6 +13,10 @@ export interface MCPService {
     api_key?: string
     token?: string
     custom_headers?: Record<string, string>
+    // Write-only flags — set to true in Update requests to explicitly remove
+    // the corresponding credential. The server never returns these fields.
+    clear_api_key?: boolean
+    clear_token?: boolean
   }
   advanced_config?: {
     timeout?: number
diff --git a/frontend/src/api/model/index.ts b/frontend/src/api/model/index.ts
index c108de4e..3ca7ac7a 100644
--- a/frontend/src/api/model/index.ts
+++ b/frontend/src/api/model/index.ts
@@ -26,6 +26,12 @@ export interface ModelConfig {
     // 会在调用远程模型 API 时附加到每个请求上。Authorization、Content-Type 等保留头会被忽略。
     custom_headers?: Record<string, string>;
     supports_vision?: boolean; // Whether the model accepts image/multimodal input
+    app_id?: string;
+    app_secret?: string;
+    // Write-only flags — set to true in Update requests to explicitly remove
+    // the corresponding credential. The server never returns these fields.
+    clear_api_key?: boolean;
+    clear_app_secret?: boolean;
   };
   is_default?: boolean;
   is_builtin?: boolean;
diff --git a/frontend/src/api/web-search-provider.ts b/frontend/src/api/web-search-provider.ts
index 1a978d9b..5c0c8c95 100644
--- a/frontend/src/api/web-search-provider.ts
+++ b/frontend/src/api/web-search-provider.ts
@@ -13,6 +13,9 @@ export interface WebSearchProviderEntity {
     base_url?: string
     proxy_url?: string
     extra_config?: Record<string, string>
+    // Write-only flag — set to true in Update requests to explicitly remove
+    // the stored API key. The server never returns this field.
+    clear_api_key?: boolean
   }
   is_default?: boolean
   created_at?: string
diff --git a/frontend/src/components/ModelEditorDialog.vue b/frontend/src/components/ModelEditorDialog.vue
index df8b45f1..6b694ed8 100644
--- a/frontend/src/components/ModelEditorDialog.vue
+++ b/frontend/src/components/ModelEditorDialog.vue
@@ -211,8 +211,16 @@
             <t-input
               v-model="formData.apiKey"
               type="password"
-              :placeholder="$t('model.editor.apiKeyPlaceholder')"
+              :disabled="formData.clearApiKey"
+              :placeholder="apiKeyPlaceholder"
             />
+            <t-checkbox
+              v-if="isEdit && formData.hasExistingApiKey"
+              v-model="formData.clearApiKey"
+              class="clear-credential"
+            >
+              {{ t('secret.clearHint') }}
+            </t-checkbox>
           </div>
 
           <!-- 自定义 HTTP Header（类似 OpenAI Python SDK 的 extra_headers） -->
@@ -331,7 +339,7 @@
 
 <script setup lang="ts">
 import { ref, watch, computed, onUnmounted, nextTick } from 'vue'
-import { MessagePlugin } from 'tdesign-vue-next'
+import { MessagePlugin, DialogPlugin } from 'tdesign-vue-next'
 import { checkOllamaModels, checkRemoteModel, testEmbeddingModel, checkRerankModel, checkASRModel, listOllamaModels, downloadOllamaModel, getDownloadProgress, checkOllamaStatus, listModelProviders, type OllamaModelInfo, type ModelProviderOption } from '@/api/initialization'
 import { getWeKnoraCloudStatus } from '@/api/model'
 import { useI18n } from 'vue-i18n'
@@ -352,6 +360,12 @@ interface ModelFormData {
   modelName: string
   baseUrl?: string
   apiKey?: string
+  // True when the server returned '***' for parameters.api_key, meaning a
+  // key is currently stored server-side. Drives the "Set / Not set" badge.
+  hasExistingApiKey?: boolean
+  // Write-only flag set by the user to explicitly remove the stored key on
+  // save. Reset to false on every dialog open.
+  clearApiKey?: boolean
   dimension?: number
   interfaceType?: 'ollama' | 'openai'
   isDefault: boolean
@@ -539,6 +553,17 @@ const dialogVisible = computed({
 
 const isEdit = computed(() => !!props.modelData)
 
+// Placeholder hint for the API key field. On edit with a stored key, swap
+// in the shared "bullets + Enter new value to replace" placeholder so the
+// input itself carries the "something is there" signal. Otherwise fall back
+// to the generic creation-mode placeholder.
+const apiKeyPlaceholder = computed(() => {
+  if (isEdit.value && formData.value.hasExistingApiKey) {
+    return t('secret.storedPlaceholder')
+  }
+  return t('model.editor.apiKeyPlaceholder')
+})
+
 const formRef = ref()
 const saving = ref(false)
 const modelChecked = ref(false)
@@ -745,8 +770,14 @@ watch(() => props.visible, (val) => {
 
     if (props.modelData) {
       // 编辑：始终用最新的 modelData 覆盖
+      // Always reset apiKey / clearApiKey on every dialog open so the
+      // invariant "non-empty apiKey means the user typed it" holds.
+      // hasExistingApiKey flows through unchanged so the badge keeps showing
+      // "Set" when the server said '***'.
       formData.value = {
         ...props.modelData,
+        apiKey: '',
+        clearApiKey: false,
         customHeaders: Array.isArray(props.modelData.customHeaders)
           ? props.modelData.customHeaders.map(h => ({ key: h.key, value: h.value }))
           : []
@@ -781,6 +812,8 @@ const resetForm = () => {
     modelName: '',
     baseUrl: '',
     apiKey: '',
+    hasExistingApiKey: false,
+    clearApiKey: false,
     dimension: undefined, // 默认不填，让用户手动输入或通过检测按钮获取
     interfaceType: undefined,
     isDefault: false,
@@ -1117,13 +1150,30 @@ const handleConfirm = async () => {
     
     // 执行表单验证
     await formRef.value?.validate()
+
+    // Confirm irrevocable credential removal before emitting.
+    if (formData.value.clearApiKey) {
+      const ok = await new Promise<boolean>((resolve) => {
+        const d = DialogPlugin.confirm({
+          header: t('secret.confirmClearTitle'),
+          body: t('secret.confirmClearBody'),
+          confirmBtn: { content: t('common.confirm'), theme: 'danger' },
+          cancelBtn: t('common.cancel'),
+          onConfirm: () => { d.hide(); resolve(true) },
+          onCancel: () => { d.hide(); resolve(false) },
+          onClose: () => { d.hide(); resolve(false) },
+        })
+      })
+      if (!ok) return
+    }
+
     saving.value = true
-    
+
     // 如果是新增且没有 id，生成一个
     if (!formData.value.id) {
       formData.value.id = generateId()
     }
-    
+
     emit('confirm', { ...formData.value })
     dialogVisible.value = false
     // 保存成功后重置草稿，下次打开新增模型时是空白
@@ -1658,6 +1708,18 @@ const handleCancel = () => {
     }
   }
 }
+
+// Destructive-action checkbox for "Remove this credential". Styled to match
+// the pattern used in McpServiceDialog so the two dialogs read identically.
+.clear-credential {
+  display: inline-flex;
+  margin-top: 8px;
+
+  :deep(.t-checkbox__label) {
+    color: var(--td-error-color);
+    font-size: 13px;
+  }
+}
 </style>
 
 <!-- 非 scoped 样式：t-select popup 渲染到 body 下，scoped 样式无法覆盖 -->
diff --git a/frontend/src/i18n/locales/en-US.ts b/frontend/src/i18n/locales/en-US.ts
index 15e7f684..fddace8d 100755
--- a/frontend/src/i18n/locales/en-US.ts
+++ b/frontend/src/i18n/locales/en-US.ts
@@ -4284,4 +4284,15 @@ export default {
       createdAt: 'Created at',
     },
   },
+  secret: {
+    // Placeholder shown inside a credential input when a value is currently
+    // stored server-side. The bullet run doubles as a visual "something is
+    // there" cue (matching how the password type renders dots); the
+    // parenthetical tells the user what typing will do.
+    storedPlaceholder: '•••••••• (Enter new value to replace)',
+    clearHint: 'Remove this credential',
+    confirmClearTitle: 'Confirm credential removal',
+    confirmClearBody:
+      'This permanently deletes the stored credential. Integrations using it will stop working. Continue?',
+  },
 }
diff --git a/frontend/src/i18n/locales/ko-KR.ts b/frontend/src/i18n/locales/ko-KR.ts
index 31e1188c..6f3aa6de 100755
--- a/frontend/src/i18n/locales/ko-KR.ts
+++ b/frontend/src/i18n/locales/ko-KR.ts
@@ -4347,4 +4347,11 @@ export default {
       createdAt: "생성 시각",
     },
   },
+  secret: {
+    storedPlaceholder: "•••••••• (새 값을 입력하면 교체됩니다)",
+    clearHint: "이 credential 제거",
+    confirmClearTitle: "credential 제거 확인",
+    confirmClearBody:
+      "저장된 credential이 영구 삭제되며, 이를 사용하는 통합이 중단됩니다. 계속할까요?",
+  },
 };
diff --git a/frontend/src/i18n/locales/ru-RU.ts b/frontend/src/i18n/locales/ru-RU.ts
index 3df18598..76755fa2 100755
--- a/frontend/src/i18n/locales/ru-RU.ts
+++ b/frontend/src/i18n/locales/ru-RU.ts
@@ -4247,4 +4247,11 @@ export default {
       createdAt: 'Создано',
     },
   },
+  secret: {
+    storedPlaceholder: '•••••••• (Введите новое значение для замены)',
+    clearHint: 'Удалить эти учётные данные',
+    confirmClearTitle: 'Подтверждение удаления учётных данных',
+    confirmClearBody:
+      'Это действие безвозвратно удалит сохранённые учётные данные. Интеграции, использующие их, перестанут работать. Продолжить?',
+  },
 }
diff --git a/frontend/src/i18n/locales/zh-CN.ts b/frontend/src/i18n/locales/zh-CN.ts
index f464f714..6d90e8c3 100755
--- a/frontend/src/i18n/locales/zh-CN.ts
+++ b/frontend/src/i18n/locales/zh-CN.ts
@@ -4280,4 +4280,11 @@ export default {
       createdAt: "创建时间",
     },
   },
+  secret: {
+    storedPlaceholder: "•••••••• (输入新值以替换)",
+    clearHint: "删除此凭据",
+    confirmClearTitle: "确认删除凭据",
+    confirmClearBody:
+      "此操作将永久删除已保存的凭据，依赖它的集成将停止工作。是否继续？",
+  },
 };
diff --git a/frontend/src/views/knowledge/settings/DataSourceEditorDialog.vue b/frontend/src/views/knowledge/settings/DataSourceEditorDialog.vue
index d213d5fc..1be97f04 100644
--- a/frontend/src/views/knowledge/settings/DataSourceEditorDialog.vue
+++ b/frontend/src/views/knowledge/settings/DataSourceEditorDialog.vue
@@ -1,6 +1,6 @@
 <script setup lang="ts">
 import { ref, computed, watch } from 'vue'
-import { MessagePlugin } from 'tdesign-vue-next'
+import { MessagePlugin, DialogPlugin } from 'tdesign-vue-next'
 import { useI18n } from 'vue-i18n'
 import {
   createDataSource,
@@ -28,6 +28,38 @@ const isEdit = computed(() => !!props.dataSource)
 const step = ref(0)
 const submitting = ref(false)
 
+// Fixed placeholder returned by the server for redacted credential strings.
+// Must match internal/types/secret.go → RedactedSecretPlaceholder.
+const REDACTED_PLACEHOLDER = '***'
+
+// Per-field: is this specific credential key stored server-side? Drives the
+// per-input placeholder swap to the "••••••• (Enter new value to replace)"
+// hint when the server marked it present.
+function hasFieldCredential(key: string): boolean {
+  return props.dataSource?.config?.credentials?.[key] === REDACTED_PLACEHOLDER
+}
+
+// Connector-level rollup: true when any credential key is stored. Used to
+// decide whether to render the "Remove all credentials" checkbox.
+const hasExistingCredentials = computed(() => {
+  const creds = props.dataSource?.config?.credentials
+  if (!creds) return false
+  return Object.values(creds).some(v => v === REDACTED_PLACEHOLDER)
+})
+
+// Placeholder for a given credential input: stored → shared hint,
+// otherwise the connector-specific default (e.g. "ntn_xxxx" for Notion).
+function credentialPlaceholder(field: { key: string; placeholder: string }): string {
+  return hasFieldCredential(field.key)
+    ? t('secret.storedPlaceholder')
+    : field.placeholder
+}
+
+// Explicit "remove all credentials" flag. Because credentials form an atomic
+// set per connector (e.g. an OAuth pair) we only support all-or-nothing
+// clearing, mirroring the backend DataSourceConfig.ClearCredentials contract.
+const clearCredentials = ref(false)
+
 // Form data
 const form = ref({
   name: '',
@@ -213,10 +245,22 @@ watch(visible, (v) => {
   selectedResourceIds.value = []
 
   if (isEdit.value && props.dataSource) {
+    // Reset clear intent on every open so an aborted deletion doesn't
+    // carry over to the next edit session.
+    clearCredentials.value = false
+    // Credentials are intentionally NOT pre-filled from the server response
+    // — even though the server returns '***' for stored secrets, the form
+    // holds an empty map. This keeps the "non-empty means user typed it"
+    // invariant that the save path relies on, and the badge reflects the
+    // stored state via hasExistingCredentials instead.
     form.value = {
       name: props.dataSource.name,
       type: props.dataSource.type,
-      config: props.dataSource.config || { credentials: {}, resource_ids: [], settings: {} },
+      config: {
+        credentials: {},
+        resource_ids: props.dataSource.config?.resource_ids || [],
+        settings: props.dataSource.config?.settings || {},
+      },
       sync_schedule: props.dataSource.sync_schedule,
       sync_mode: props.dataSource.sync_mode,
       conflict_strategy: props.dataSource.conflict_strategy,
@@ -225,6 +269,7 @@ watch(visible, (v) => {
     selectedResourceIds.value = form.value.config?.resource_ids || []
     tempDsId.value = props.dataSource.id
   } else {
+    clearCredentials.value = false
     form.value = {
       name: '',
       type: '',
@@ -405,8 +450,45 @@ function prevStep() {
   step.value--
 }
 
+// Prompt the user before irrevocable credential removal.
+function confirmClearIfNeeded(): Promise<boolean> {
+  if (!clearCredentials.value) return Promise.resolve(true)
+  return new Promise((resolve) => {
+    const d = DialogPlugin.confirm({
+      header: t('secret.confirmClearTitle'),
+      body: t('secret.confirmClearBody'),
+      confirmBtn: { content: t('common.confirm'), theme: 'danger' },
+      cancelBtn: t('common.cancel'),
+      onConfirm: () => { d.hide(); resolve(true) },
+      onCancel: () => { d.hide(); resolve(false) },
+      onClose: () => { d.hide(); resolve(false) },
+    })
+  })
+}
+
+// Build the config payload for Create / Update requests. In edit mode this
+// applies write-only secret semantics:
+//   - clearCredentials checked → send clear_credentials: true (backend wipes)
+//   - user typed credential values → send them as-is
+//   - user left fields blank → send empty credentials map (backend preserves
+//     every existing credential key individually)
+function buildConfigPayload(): Record<string, unknown> {
+  const cfg: Record<string, unknown> = {
+    credentials: clearCredentials.value ? {} : { ...form.value.config.credentials },
+    resource_ids: form.value.config.resource_ids,
+    settings: form.value.config.settings,
+  }
+  if (clearCredentials.value) {
+    cfg.clear_credentials = true
+  }
+  return cfg
+}
+
 // --- Final submit ---
 async function handleSubmit() {
+  const ok = await confirmClearIfNeeded()
+  if (!ok) return
+
   form.value.config.resource_ids = selectedResourceIds.value
   submitting.value = true
   try {
@@ -415,12 +497,14 @@ async function handleSubmit() {
     if (tempDsId.value) {
       await updateDataSource(tempDsId.value, {
         ...form.value,
+        config: buildConfigPayload(),
         knowledge_base_id: props.kbId,
         status: 'active',
       } as any)
     } else {
       const res = await createDataSource({
         ...form.value,
+        config: buildConfigPayload(),
         knowledge_base_id: props.kbId,
         status: 'active',
       } as any)
@@ -575,6 +659,14 @@ const stepTitles = computed(() => [
         </a>
       </div>
 
+      <!--
+        Credential fields. When the server returned '***' for a field the
+        per-input placeholder swaps to the shared "••••••• (Enter new value
+        to replace)" hint so the input carries the "something is stored"
+        signal without a separate badge. The "Remove all credentials"
+        checkbox below handles the destructive clear for the whole set
+        (DataSource credentials are per-connector atomic bundles).
+      -->
       <div v-for="field in currentDef?.fields || []" :key="field.key" class="form-item">
         <label class="form-label">
           {{ t(field.labelKey) }}
@@ -582,12 +674,19 @@ const stepTitles = computed(() => [
         </label>
         <t-input
           v-model="form.config.credentials[field.key]"
-          :placeholder="field.placeholder"
+          :disabled="clearCredentials"
+          :placeholder="credentialPlaceholder(field)"
           :type="field.secret ? 'password' : 'text'"
         />
         <div v-if="field.hintKey" class="form-hint">{{ t(field.hintKey) }}</div>
       </div>
 
+      <div v-if="isEdit && hasExistingCredentials" class="form-item">
+        <t-checkbox v-model="clearCredentials" class="clear-credential">
+          {{ t('secret.clearHint') }}
+        </t-checkbox>
+      </div>
+
       <div class="form-actions">
         <t-button variant="outline" :loading="testing" @click="testConnection">
           {{ t('datasource.testConnection') }}
@@ -886,6 +985,12 @@ const stepTitles = computed(() => [
 .form-item { margin-bottom: 16px; }
 .form-label { display: block; font-size: 13px; font-weight: 500; margin-bottom: 6px; color: var(--td-text-color-primary); }
 .required-mark { color: var(--td-error-color); margin-left: 2px; }
+
+/* Destructive-action checkbox — red label, matches the other 3 dialogs. */
+.clear-credential :deep(.t-checkbox__label) {
+  color: var(--td-error-color);
+  font-size: 13px;
+}
 .form-tip { font-size: 12px; color: var(--td-text-color-placeholder); margin: 4px 0 12px; }
 .form-hint { font-size: 12px; color: var(--td-text-color-placeholder); margin-top: 6px; line-height: 1.5; }
 .form-actions { display: flex; align-items: center; gap: 8px; margin-top: 12px; }
diff --git a/frontend/src/views/settings/ModelSettings.vue b/frontend/src/views/settings/ModelSettings.vue
index 70e63c60..bdbb14ab 100644
--- a/frontend/src/views/settings/ModelSettings.vue
+++ b/frontend/src/views/settings/ModelSettings.vue
@@ -138,6 +138,13 @@ const backendTypeToModelType: Record<string, ModelType> = {
 }
 
 // 将后端模型格式转换为旧的前端格式（附带 _modelType 便于渲染）
+// NOTE: apiKey is intentionally NEVER pre-filled from the server response.
+// The server returns '***' as a redacted placeholder when a key is stored,
+// and '' when it is not. We expose this as hasExistingApiKey so the editor
+// dialog can render a "Set / Not set" badge, while the apiKey field starts
+// blank — this preserves the invariant "non-empty formData.apiKey means the
+// user typed something" that the save path relies on to decide preserve /
+// replace / clear.
 function convertToLegacyFormat(model: ModelConfig) {
   return {
     id: model.id!,
@@ -145,7 +152,8 @@ function convertToLegacyFormat(model: ModelConfig) {
     source: model.source,
     modelName: model.name,
     baseUrl: model.parameters.base_url || '',
-    apiKey: model.parameters.api_key || '',
+    apiKey: '',
+    hasExistingApiKey: model.parameters.api_key === '***',
     provider: model.parameters.provider || '',
     dimension: model.parameters.embedding_parameters?.dimension,
     isBuiltin: model.is_builtin || false,
@@ -283,6 +291,20 @@ const handleModelSave = async (modelData: any) => {
       }
     }
 
+    // 将前端格式转换为后端格式.
+    // Three-state api_key semantics (write-only secrets pattern):
+    //   - clearApiKey set                → send { clear_api_key: true }
+    //   - user typed a value             → send { api_key: "..." }
+    //   - empty (default on edit)        → omit api_key → server preserves
+    //   - empty on create                → omit api_key → no stored secret
+    const trimmedApiKey = (modelData.apiKey ?? '').trim()
+    const apiKeyFields: { api_key?: string; clear_api_key?: boolean } =
+      modelData.clearApiKey
+        ? { clear_api_key: true }
+        : trimmedApiKey
+          ? { api_key: trimmedApiKey }
+          : {}
+
     const apiModelData: ModelConfig = {
       name: modelData.modelName.trim(),
       type: getModelType(currentModelType.value),
@@ -290,7 +312,7 @@ const handleModelSave = async (modelData: any) => {
       description: '',
       parameters: {
         base_url: modelData.baseUrl?.trim() || '',
-        api_key: modelData.apiKey?.trim() || '',
+        ...apiKeyFields,
         provider: modelData.provider || '',
         ...(Object.keys(customHeadersMap).length > 0 ? { custom_headers: customHeadersMap } : {}),
         ...(currentModelType.value === 'embedding' && modelData.dimension ? {
diff --git a/frontend/src/views/settings/WebSearchSettings.vue b/frontend/src/views/settings/WebSearchSettings.vue
index e216a9cd..8fd0b506 100644
--- a/frontend/src/views/settings/WebSearchSettings.vue
+++ b/frontend/src/views/settings/WebSearchSettings.vue
@@ -98,13 +98,22 @@
               :placeholder="t('webSearchSettings.baseUrlPlaceholder')"
             />
           </t-form-item>
-          <t-form-item v-if="selectedProviderType?.requires_api_key" :label="t('webSearchSettings.apiKeyLabel')" name="parameters.api_key">
+          <!--
+            API key is mandatory for every requires_api_key=true provider
+            (Bing / Google / Tavily / Ollama / Baidu — see
+            validateProviderParameters in service/web_search_provider.go),
+            so the "Remove this credential" affordance shown in the other
+            three dialogs is intentionally omitted here. Revoking access
+            means deleting the whole provider row from the list.
+          -->
+          <div v-if="selectedProviderType?.requires_api_key" class="credential-field">
+            <label class="credential-label">{{ t('webSearchSettings.apiKeyLabel') }}</label>
             <t-input
               v-model="providerForm.parameters.api_key"
               type="password"
-              :placeholder="editingProvider ? t('webSearchSettings.apiKeyUnchanged') : t('webSearchSettings.apiKeyPlaceholder')"
+              :placeholder="apiKeyPlaceholder"
             />
-          </t-form-item>
+          </div>
           <t-form-item v-if="selectedProviderType?.requires_engine_id" :label="t('webSearchSettings.engineIdLabel')" name="parameters.engine_id">
             <t-input v-model="providerForm.parameters.engine_id" :placeholder="t('webSearchSettings.engineIdLabel')" />
           </t-form-item>
@@ -179,6 +188,10 @@ const testingId = ref<string | null>(null)
 const saving = ref(false)
 const formRef = ref<any>()
 
+// Fixed placeholder returned by the server for redacted secrets. Must match
+// internal/types/secret.go → RedactedSecretPlaceholder.
+const REDACTED_PLACEHOLDER = '***'
+
 const providerForm = ref<{
   name: string
   provider: string
@@ -198,6 +211,23 @@ const selectedProviderType = computed(() => {
   return providerTypes.value.find(pt => pt.id === providerForm.value.provider)
 })
 
+// "Is an API key currently stored?" is signaled by the server returning the
+// fixed REDACTED_PLACEHOLDER in the response. Drive the label badge from this.
+const hasExistingApiKey = computed(() => {
+  return editingProvider.value?.parameters?.api_key === REDACTED_PLACEHOLDER
+})
+
+// In edit mode with a stored key, swap the placeholder to the shared
+// "bullets + Enter new value to replace" hint. Otherwise fall back to the
+// provider-specific placeholder (creation) or the "leave blank to keep"
+// copy used when no key is stored yet.
+const apiKeyPlaceholder = computed(() => {
+  if (!editingProvider.value) return t('webSearchSettings.apiKeyPlaceholder')
+  return hasExistingApiKey.value
+    ? t('secret.storedPlaceholder')
+    : t('webSearchSettings.apiKeyUnchanged')
+})
+
 const isProviderFree = (providerType: WebSearchProviderTypeInfo) => {
   // "Free" here means no upstream-paid credentials are required. Self-hosted
   // providers (requires_base_url) are still free to use even though they need
@@ -253,6 +283,8 @@ const editProvider = (entity: WebSearchProviderEntity) => {
     provider: entity.provider,
     description: entity.description || '',
     parameters: {
+      // Never pre-fill the api_key — even the redacted placeholder from the
+      // server is ignored so that "non-empty means user typed it" holds.
       api_key: '',
       engine_id: entity.parameters?.engine_id || '',
       base_url: entity.parameters?.base_url || '',
@@ -273,18 +305,29 @@ const saveProvider = async () => {
 
   saving.value = true
   try {
+    // Build the parameters payload using two-state semantics:
+    //   - user typed a value → send api_key (replaces stored)
+    //   - empty + editing → omit api_key (server preserves stored value)
+    //   - empty + creating → omit api_key (no secret to store yet)
+    // No clear path: every requires_api_key provider mandates a value, so
+    // "revoke" means deleting the provider row, not zeroing the key.
+    const paramsOut: WebSearchProviderEntity['parameters'] = {
+      engine_id: providerForm.value.parameters.engine_id,
+      base_url: providerForm.value.parameters.base_url,
+      proxy_url: providerForm.value.parameters.proxy_url,
+    }
+    if (providerForm.value.parameters.api_key) {
+      paramsOut.api_key = providerForm.value.parameters.api_key
+    }
+
     const data: Partial<WebSearchProviderEntity> = {
       name: providerForm.value.name.trim() || selectedProviderType.value?.name || providerForm.value.provider,
       provider: providerForm.value.provider as any,
       description: providerForm.value.description,
-      parameters: { ...providerForm.value.parameters },
+      parameters: paramsOut,
       is_default: providerForm.value.is_default,
     }
 
-    if (editingProvider.value && !data.parameters!.api_key) {
-      delete data.parameters!.api_key
-    }
-
     if (editingProvider.value) {
       await updateWebSearchProvider(editingProvider.value.id!, data)
       MessagePlugin.success(t('webSearchSettings.toasts.providerUpdated'))
@@ -471,6 +514,31 @@ onMounted(async () => {
   margin: 20px 0;
 }
 
+/**
+ * Credential field: stacks the label row, password input, and the optional
+ * "Remove this credential" checkbox vertically. Matches the pattern in
+ * McpServiceDialog and ModelEditorDialog so the whole UI reads consistently.
+ */
+.credential-field {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  margin-bottom: 20px;
+}
+
+.credential-label {
+  display: block;
+  font-size: 14px;
+  color: var(--td-text-color-primary);
+}
+
+.clear-credential {
+  :deep(.t-checkbox__label) {
+    color: var(--td-error-color);
+    font-size: 13px;
+  }
+}
+
 .credentials-hint {
   margin-bottom: 12px;
   font-size: 13px;
diff --git a/frontend/src/views/settings/components/McpServiceDialog.vue b/frontend/src/views/settings/components/McpServiceDialog.vue
index 1ae70d72..23a28a49 100644
--- a/frontend/src/views/settings/components/McpServiceDialog.vue
+++ b/frontend/src/views/settings/components/McpServiceDialog.vue
@@ -34,8 +34,8 @@
       </t-form-item>
 
       <!-- URL for SSE/HTTP Streamable -->
-      <t-form-item 
-        :label="t('mcpServiceDialog.serviceUrl')" 
+      <t-form-item
+        :label="t('mcpServiceDialog.serviceUrl')"
         name="url"
       >
         <t-input v-model="formData.url" :placeholder="t('mcpServiceDialog.serviceUrlPlaceholder')" />
@@ -50,20 +50,47 @@
       <!-- Authentication Config -->
       <t-collapse :default-value="[]">
         <t-collapse-panel :header="t('mcpServiceDialog.authConfig')" value="auth">
-          <t-form-item :label="t('mcpServiceDialog.apiKey')">
+          <!--
+            Credential fields follow the "write-only secrets" pattern.
+            When a value is currently stored on the server the placeholder
+            is swapped for a bullet run + "Enter new value to replace"
+            hint, so the visual "something is there" signal is carried by
+            the input itself rather than by a separate Set/Not-set badge.
+            The Remove checkbox still offers an explicit clear path.
+          -->
+          <div class="credential-field">
+            <label class="credential-label">{{ t('mcpServiceDialog.apiKey') }}</label>
             <t-input
               v-model="formData.auth_config.api_key"
               type="password"
-              :placeholder="t('mcpServiceDialog.optional')"
+              :disabled="clearApiKey"
+              :placeholder="apiKeyPlaceholder"
             />
-          </t-form-item>
-          <t-form-item :label="t('mcpServiceDialog.bearerToken')">
+            <t-checkbox
+              v-if="mode === 'edit' && hasExistingApiKey"
+              v-model="clearApiKey"
+              class="clear-credential"
+            >
+              {{ t('secret.clearHint') }}
+            </t-checkbox>
+          </div>
+
+          <div class="credential-field">
+            <label class="credential-label">{{ t('mcpServiceDialog.bearerToken') }}</label>
             <t-input
               v-model="formData.auth_config.token"
               type="password"
-              :placeholder="t('mcpServiceDialog.optional')"
+              :disabled="clearToken"
+              :placeholder="tokenPlaceholder"
             />
-          </t-form-item>
+            <t-checkbox
+              v-if="mode === 'edit' && hasExistingToken"
+              v-model="clearToken"
+              class="clear-credential"
+            >
+              {{ t('secret.clearHint') }}
+            </t-checkbox>
+          </div>
         </t-collapse-panel>
 
         <!-- Advanced Config -->
@@ -100,7 +127,7 @@
 
 <script setup lang="ts">
 import { ref, watch, computed } from 'vue'
-import { MessagePlugin } from 'tdesign-vue-next'
+import { MessagePlugin, DialogPlugin } from 'tdesign-vue-next'
 import type { FormInstanceFunctions, FormRule } from 'tdesign-vue-next'
 import { useI18n } from 'vue-i18n'
 import {
@@ -128,6 +155,10 @@ const formRef = ref<FormInstanceFunctions>()
 const submitting = ref(false)
 const { t } = useI18n()
 
+// Fixed placeholder returned by the server for sensitive fields whose values
+// are withheld. Must match internal/types/secret.go → RedactedSecretPlaceholder.
+const REDACTED_PLACEHOLDER = '***'
+
 const formData = ref({
   name: '',
   description: '',
@@ -145,11 +176,40 @@ const formData = ref({
   }
 })
 
+// Explicit "remove stored credential" flags. Reset to false on every open/reset.
+const clearApiKey = ref(false)
+const clearToken = ref(false)
+
+// "Is a credential currently stored?" is signaled by the server returning the
+// fixed REDACTED_PLACEHOLDER instead of an empty string. Drive the label
+// badge and placeholder hint from this signal.
+const hasExistingApiKey = computed(
+  () => props.service?.auth_config?.api_key === REDACTED_PLACEHOLDER
+)
+const hasExistingToken = computed(
+  () => props.service?.auth_config?.token === REDACTED_PLACEHOLDER
+)
+
+// Placeholders swap to the shared "stored credential" hint when the server
+// signals a value is present (parameters come back as '***'). Otherwise
+// the field is genuinely empty and we fall through to the normal
+// "Optional" placeholder that appears in add mode too.
+const apiKeyPlaceholder = computed(() =>
+  hasExistingApiKey.value
+    ? t('secret.storedPlaceholder')
+    : t('mcpServiceDialog.optional')
+)
+const tokenPlaceholder = computed(() =>
+  hasExistingToken.value
+    ? t('secret.storedPlaceholder')
+    : t('mcpServiceDialog.optional')
+)
+
 const rules: Record<string, FormRule[]> = {
   name: [{ required: true, message: t('mcpServiceDialog.rules.nameRequired') as string, type: 'error' }],
   transport_type: [{ required: true, message: t('mcpServiceDialog.rules.transportRequired') as string, type: 'error' }],
   url: [
-    { 
+    {
       validator: (val: string) => {
         if (!val || val.trim() === '') {
           return { result: false, message: t('mcpServiceDialog.rules.urlRequired') as string, type: 'error' }
@@ -171,7 +231,10 @@ const dialogVisible = computed({
   set: (value) => emit('update:visible', value)
 })
 
-// Reset form function - defined before watch to avoid hoisting issues
+// Reset form function — defined before watch to avoid hoisting issues.
+// Sensitive fields are always blank: the watch below does not copy the
+// server-provided redacted placeholder into formData, and clear flags are
+// reset so a reopen does not carry over an aborted deletion intent.
 const resetForm = () => {
   formData.value = {
     name: '',
@@ -189,10 +252,16 @@ const resetForm = () => {
       retry_delay: 1
     }
   }
+  clearApiKey.value = false
+  clearToken.value = false
   formRef.value?.clearValidate()
 }
 
-// Watch service prop to initialize form
+// Watch service prop to initialize form.
+// Sensitive fields (api_key, token) are NEVER pre-filled from the server
+// response — even when the server returns '***' indicating a stored value.
+// This keeps the "non-empty means user typed it" invariant that the submit
+// logic relies on to decide between preserve and replace.
 watch(
   () => props.service,
   (service) => {
@@ -206,8 +275,8 @@ watch(
         transport_type: transportType as 'sse' | 'http-streamable',
         url: service.url || '',
         auth_config: {
-          api_key: service.auth_config?.api_key || '',
-          token: service.auth_config?.token || ''
+          api_key: '',
+          token: ''
         },
         advanced_config: {
           timeout: service.advanced_config?.timeout || 30,
@@ -215,6 +284,8 @@ watch(
           retry_delay: service.advanced_config?.retry_delay || 1
         }
       }
+      clearApiKey.value = false
+      clearToken.value = false
     } else {
       resetForm()
     }
@@ -222,24 +293,67 @@ watch(
   { immediate: true }
 )
 
-// Handle submit
+// Prompt the user before irrevocable credential removal.
+const confirmClearIfNeeded = (): Promise<boolean> => {
+  if (!clearApiKey.value && !clearToken.value) return Promise.resolve(true)
+  return new Promise((resolve) => {
+    const d = DialogPlugin.confirm({
+      header: t('secret.confirmClearTitle'),
+      body: t('secret.confirmClearBody'),
+      confirmBtn: { content: t('common.confirm'), theme: 'danger' },
+      cancelBtn: t('common.cancel'),
+      onConfirm: () => {
+        d.hide()
+        resolve(true)
+      },
+      onCancel: () => {
+        d.hide()
+        resolve(false)
+      },
+      onClose: () => {
+        d.hide()
+        resolve(false)
+      }
+    })
+  })
+}
+
+// Handle submit — three-state auth_config payload:
+//   - clear flag set → send { clear_api_key: true } / { clear_token: true }
+//   - user typed a value → send the value
+//   - otherwise → omit the field, server preserves the stored value
+// If auth_config would be empty, omit the key entirely.
 const handleSubmit = async () => {
   const valid = await formRef.value?.validate()
   if (!valid) return
 
+  const proceed = await confirmClearIfNeeded()
+  if (!proceed) return
+
   submitting.value = true
   try {
+    const authPayload: Record<string, unknown> = {}
+    if (clearApiKey.value) {
+      authPayload.clear_api_key = true
+    } else if (formData.value.auth_config.api_key) {
+      authPayload.api_key = formData.value.auth_config.api_key
+    }
+    if (clearToken.value) {
+      authPayload.clear_token = true
+    } else if (formData.value.auth_config.token) {
+      authPayload.token = formData.value.auth_config.token
+    }
+
     const data: Partial<MCPService> = {
       name: formData.value.name,
       description: formData.value.description,
       enabled: formData.value.enabled,
       transport_type: formData.value.transport_type,
-      auth_config: {
-        api_key: formData.value.auth_config.api_key || undefined,
-        token: formData.value.auth_config.token || undefined
-      },
       advanced_config: formData.value.advanced_config,
-      url: formData.value.url || undefined
+      url: formData.value.url || undefined,
+    }
+    if (Object.keys(authPayload).length > 0) {
+      data.auth_config = authPayload as MCPService['auth_config']
     }
 
     if (props.mode === 'add') {
@@ -269,5 +383,37 @@ const handleClose = () => {
 
 <style scoped lang="less">
 /* Stdio-related styles removed as stdio transport is disabled for security reasons */
+
+/**
+ * Credential field: stacks the label row, the password input, and the
+ * optional "Remove this credential" checkbox vertically. Replaces the
+ * t-form-item-based layout for the auth-config fields so the inline badge
+ * doesn't get clipped by the form's 120px label-width and the clear
+ * checkbox doesn't sit alongside the input.
+ */
+.credential-field {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  margin-bottom: 20px;
+
+  &:last-child {
+    margin-bottom: 0;
+  }
+}
+
+.credential-label {
+  display: block;
+  font-size: 14px;
+  color: var(--td-text-color-primary);
+  line-height: 22px;
+}
+
+.clear-credential {
+  :deep(.t-checkbox__label) {
+    color: var(--td-error-color);
+    font-size: 13px;
+  }
+}
 </style>
 
diff --git a/internal/application/service/datasource_service.go b/internal/application/service/datasource_service.go
index bf818c1f..7fcd2352 100644
--- a/internal/application/service/datasource_service.go
+++ b/internal/application/service/datasource_service.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"mime/multipart"
 	"net/textproto"
+	"reflect"
 	"time"
 
 	"github.com/Tencent/WeKnora/internal/datasource"
@@ -15,6 +16,7 @@ import (
 	"github.com/Tencent/WeKnora/internal/tracing/langfuse"
 	"github.com/Tencent/WeKnora/internal/types"
 	"github.com/Tencent/WeKnora/internal/types/interfaces"
+	secutils "github.com/Tencent/WeKnora/internal/utils"
 	"github.com/hibiken/asynq"
 )
 
@@ -153,8 +155,55 @@ func (s *DataSourceService) UpdateDataSource(ctx context.Context, ds *types.Data
 		return nil, datasource.ErrDataSourceInvalid
 	}
 
-	// Validate new configuration if changed
-	if ds.Type != existing.Type || string(ds.Config) != string(existing.Config) {
+	// Apply write-only secret merge semantics to the Config jsonb:
+	// empty / redacted credential strings preserve existing values,
+	// ClearCredentials wipes the whole map, other values replace. This
+	// blocks the NELO-1299-style round-trip bug where a frontend that
+	// echoed back the redacted placeholder would overwrite real secrets.
+	//
+	// We also remember the parsed configs for the post-merge "changed?"
+	// comparison — a raw-bytes compare against ds.Config is unreliable
+	// because Go map iteration order makes the re-serialized JSON's key
+	// ordering nondeterministic, causing string(merged) != string(existing)
+	// to spuriously trip every time.
+	var mergedCfg, existingParsedCfg *types.DataSourceConfig
+	if len(ds.Config) > 0 {
+		incomingCfg, parseIncErr := ds.ParseConfig()
+		existingCfg, parseExErr := existing.ParseConfig()
+		if parseIncErr == nil && parseExErr == nil && incomingCfg != nil {
+			baseExisting := types.DataSourceConfig{}
+			if existingCfg != nil {
+				baseExisting = *existingCfg
+			}
+			if incomingCfg.ClearCredentials {
+				logger.Infof(ctx, "DataSource credentials cleared by user: id=%s",
+					secutils.SanitizeForLog(ds.ID))
+			}
+			merged := incomingCfg.MergeUpdate(baseExisting)
+			if blob, err := merged.ToJSON(); err == nil {
+				ds.Config = blob
+			}
+			mergedCfg = &merged
+			existingParsedCfg = existingCfg
+		}
+	}
+
+	// Validate new configuration if changed. Compare parsed structures to
+	// avoid re-running (potentially expensive) OAuth / live-connection
+	// validators on every update that only re-orders JSON keys.
+	//
+	// Skip validation entirely when the user is explicitly revoking
+	// credentials (ClearCredentials=true). Live validators (e.g. Notion's
+	// /me API) require a working secret by definition; trying to validate
+	// after a wipe would always fail and leave the row un-cleared, defeating
+	// the whole point of the "Remove all credentials" affordance.
+	configActuallyChanged := true
+	if mergedCfg != nil && existingParsedCfg != nil {
+		configActuallyChanged = !reflect.DeepEqual(*mergedCfg, *existingParsedCfg)
+	}
+	clearingCredentials := mergedCfg != nil && !mergedCfg.HasCredentials() &&
+		existingParsedCfg != nil && existingParsedCfg.HasCredentials()
+	if !clearingCredentials && (ds.Type != existing.Type || configActuallyChanged) {
 		if err := s.validateDataSourceConfig(ctx, ds); err != nil {
 			return nil, err
 		}
diff --git a/internal/application/service/mcp_service.go b/internal/application/service/mcp_service.go
index a7c5b18d..20dda251 100644
--- a/internal/application/service/mcp_service.go
+++ b/internal/application/service/mcp_service.go
@@ -3,6 +3,8 @@ package service
 import (
 	"context"
 	"fmt"
+	"maps"
+	"slices"
 	"time"
 
 	"github.com/Tencent/WeKnora/internal/logger"
@@ -53,7 +55,12 @@ func (s *mcpServiceService) CreateMCPService(ctx context.Context, service *types
 	return nil
 }
 
-// GetMCPServiceByID retrieves an MCP service by ID
+// GetMCPServiceByID retrieves an MCP service by ID.
+//
+// Sensitive fields are redacted before the service is returned so that the
+// single-resource GET behaves consistently with the list endpoint. Builtin
+// services still route through HideSensitiveInfo which clears additional
+// fields (URL, Headers, EnvVars, StdioConfig) on top of the redaction.
 func (s *mcpServiceService) GetMCPServiceByID(
 	ctx context.Context,
 	tenantID uint64,
@@ -69,6 +76,10 @@ func (s *mcpServiceService) GetMCPServiceByID(
 		return nil, fmt.Errorf("MCP service not found")
 	}
 
+	if service.IsBuiltin {
+		return service.HideSensitiveInfo(), nil
+	}
+	service.RedactSensitiveData()
 	return service, nil
 }
 
@@ -80,12 +91,14 @@ func (s *mcpServiceService) ListMCPServices(ctx context.Context, tenantID uint64
 		return nil, fmt.Errorf("failed to list MCP services: %w", err)
 	}
 
-	// Mask sensitive data for list view
+	// Redact sensitive data before returning so secrets never leave the server.
+	// Builtin services go through HideSensitiveInfo which clears additional
+	// fields (URL, headers, env_vars, stdio_config) beyond redaction.
 	for i, service := range services {
 		if service.IsBuiltin {
 			services[i] = service.HideSensitiveInfo()
 		} else {
-			service.MaskSensitiveData()
+			service.RedactSensitiveData()
 		}
 	}
 
@@ -141,6 +154,57 @@ func (s *mcpServiceService) UpdateMCPService(ctx context.Context, service *types
 	// Store old enabled state BEFORE any updates
 	oldEnabled := existing.Enabled
 
+	// Snapshot pre-merge values of fields that drive configChanged. We need
+	// this because the in-place merge below reassigns pointer fields such as
+	// existing.URL = service.URL, after which any post-merge comparison
+	// between service.URL and existing.URL would trivially match.
+	preURL := ""
+	preURLSet := existing.URL != nil
+	if preURLSet {
+		preURL = *existing.URL
+	}
+	var preStdioCommand string
+	var preStdioArgs []string
+	preStdioSet := existing.StdioConfig != nil
+	if preStdioSet {
+		preStdioCommand = existing.StdioConfig.Command
+		preStdioArgs = append([]string(nil), existing.StdioConfig.Args...)
+	}
+	preTransportType := existing.TransportType
+	preAuthSet := existing.AuthConfig != nil
+	var preAuthAPIKey, preAuthToken string
+	var preAuthHeaders map[string]string
+	if preAuthSet {
+		preAuthAPIKey = existing.AuthConfig.APIKey
+		preAuthToken = existing.AuthConfig.Token
+		// Copy the map so subsequent mutations via merged.CustomHeaders don't
+		// alias into the snapshot.
+		if existing.AuthConfig.CustomHeaders != nil {
+			preAuthHeaders = make(map[string]string, len(existing.AuthConfig.CustomHeaders))
+			maps.Copy(preAuthHeaders, existing.AuthConfig.CustomHeaders)
+		}
+	}
+
+	// AuthConfig merge is applied unconditionally (both partial and full
+	// updates), so a request body like {"clear_token": true} by itself is
+	// honored instead of being silently dropped when Name is empty.
+	// Audit-log explicit clear operations before the merge absorbs the flag.
+	if service.AuthConfig != nil {
+		if service.AuthConfig.ClearAPIKey {
+			logger.GetLogger(ctx).Infof(
+				"MCP auth cleared by user: id=%s field=api_key",
+				secutils.SanitizeForLog(service.ID),
+			)
+		}
+		if service.AuthConfig.ClearToken {
+			logger.GetLogger(ctx).Infof(
+				"MCP auth cleared by user: id=%s field=token",
+				secutils.SanitizeForLog(service.ID),
+			)
+		}
+		existing.AuthConfig = service.AuthConfig.MergeUpdate(existing.AuthConfig)
+	}
+
 	// Merge updates: only update fields that are provided (non-zero or explicitly set)
 	// This ensures that false values for enabled field are properly updated
 	// Handler ensures that service.Enabled is only set if "enabled" key exists in the request
@@ -148,7 +212,7 @@ func (s *mcpServiceService) UpdateMCPService(ctx context.Context, service *types
 	// or if we're updating other fields (indicating full update)
 	// For enabled field, we'll update it if this is a partial update (only enabled) or if it's explicitly set
 	if service.Name == "" {
-		// Partial update - only update enabled field
+		// Partial update - only update enabled field (AuthConfig already merged above).
 		existing.Enabled = service.Enabled
 	} else {
 		// Full update - update all fields including enabled
@@ -172,9 +236,6 @@ func (s *mcpServiceService) UpdateMCPService(ctx context.Context, service *types
 		if service.Headers != nil {
 			existing.Headers = service.Headers
 		}
-		if service.AuthConfig != nil {
-			existing.AuthConfig = service.AuthConfig
-		}
 		if service.AdvancedConfig != nil {
 			existing.AdvancedConfig = service.AdvancedConfig
 		}
@@ -188,25 +249,39 @@ func (s *mcpServiceService) UpdateMCPService(ctx context.Context, service *types
 		return fmt.Errorf("failed to update MCP service: %w", err)
 	}
 
-	// Check if critical configuration changed (URL/StdioConfig, transport type, or auth config)
+	// Check if critical configuration changed (URL / StdioConfig / transport
+	// type / auth config). Comparisons MUST be against the pre-merge
+	// snapshots captured above — after the in-place merge, service.URL and
+	// existing.URL point to the same memory, making any post-merge compare
+	// vacuously equal. Saving the dialog without touching these fields must
+	// not recycle the live MCP client connection (that's the NELO-1299
+	// regression we're preventing).
 	configChanged := false
-	if service.URL != nil && existing.URL != nil && *service.URL != *existing.URL {
+	currURLSet := existing.URL != nil
+	switch {
+	case currURLSet != preURLSet:
 		configChanged = true
-	} else if (service.URL != nil) != (existing.URL != nil) {
+	case currURLSet && *existing.URL != preURL:
 		configChanged = true
 	}
-	if service.StdioConfig != nil && existing.StdioConfig != nil {
-		if service.StdioConfig.Command != existing.StdioConfig.Command ||
-			!equalStringSlices(service.StdioConfig.Args, existing.StdioConfig.Args) {
-			configChanged = true
-		}
-	} else if (service.StdioConfig != nil) != (existing.StdioConfig != nil) {
+	currStdioSet := existing.StdioConfig != nil
+	switch {
+	case currStdioSet != preStdioSet:
+		configChanged = true
+	case currStdioSet && (existing.StdioConfig.Command != preStdioCommand ||
+		!slices.Equal(existing.StdioConfig.Args, preStdioArgs)):
 		configChanged = true
 	}
-	if service.TransportType != "" && service.TransportType != existing.TransportType {
+	if existing.TransportType != preTransportType {
 		configChanged = true
 	}
-	if service.AuthConfig != nil {
+	currAuthSet := existing.AuthConfig != nil
+	switch {
+	case currAuthSet != preAuthSet:
+		configChanged = true
+	case currAuthSet && (existing.AuthConfig.APIKey != preAuthAPIKey ||
+		existing.AuthConfig.Token != preAuthToken ||
+		!maps.Equal(existing.AuthConfig.CustomHeaders, preAuthHeaders)):
 		configChanged = true
 	}
 	name := secutils.SanitizeForLog(existing.Name)
@@ -393,15 +468,3 @@ func (s *mcpServiceService) GetMCPServiceResources(
 	return resources, nil
 }
 
-// equalStringSlices compares two string slices for equality
-func equalStringSlices(a, b []string) bool {
-	if len(a) != len(b) {
-		return false
-	}
-	for i := range a {
-		if a[i] != b[i] {
-			return false
-		}
-	}
-	return true
-}
diff --git a/internal/application/service/mcp_service_test.go b/internal/application/service/mcp_service_test.go
new file mode 100644
index 00000000..af6a4fc6
--- /dev/null
+++ b/internal/application/service/mcp_service_test.go
@@ -0,0 +1,395 @@
+package service
+
+import (
+	"context"
+	"testing"
+
+	"github.com/Tencent/WeKnora/internal/mcp"
+	"github.com/Tencent/WeKnora/internal/types"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// fakeMCPRepo is a minimal in-memory implementation of
+// interfaces.MCPServiceRepository for testing the service-layer merge logic
+// without depending on the database.
+type fakeMCPRepo struct {
+	store map[string]*types.MCPService
+}
+
+func newFakeMCPRepo() *fakeMCPRepo {
+	return &fakeMCPRepo{store: make(map[string]*types.MCPService)}
+}
+
+func (r *fakeMCPRepo) Create(_ context.Context, s *types.MCPService) error {
+	r.store[s.ID] = s
+	return nil
+}
+
+func (r *fakeMCPRepo) GetByID(_ context.Context, _ uint64, id string) (*types.MCPService, error) {
+	s, ok := r.store[id]
+	if !ok {
+		return nil, nil
+	}
+	// return a deep-ish copy so service-layer mutations to the returned value
+	// do not leak back into the fake store, mirroring how GORM produces a
+	// fresh struct per query
+	cp := *s
+	if s.AuthConfig != nil {
+		ac := *s.AuthConfig
+		cp.AuthConfig = &ac
+	}
+	if s.AdvancedConfig != nil {
+		adv := *s.AdvancedConfig
+		cp.AdvancedConfig = &adv
+	}
+	return &cp, nil
+}
+
+func cloneService(s *types.MCPService) *types.MCPService {
+	cp := *s
+	if s.AuthConfig != nil {
+		ac := *s.AuthConfig
+		cp.AuthConfig = &ac
+	}
+	if s.AdvancedConfig != nil {
+		adv := *s.AdvancedConfig
+		cp.AdvancedConfig = &adv
+	}
+	return &cp
+}
+
+func (r *fakeMCPRepo) List(_ context.Context, _ uint64) ([]*types.MCPService, error) {
+	out := make([]*types.MCPService, 0, len(r.store))
+	for _, s := range r.store {
+		out = append(out, cloneService(s))
+	}
+	return out, nil
+}
+
+func (r *fakeMCPRepo) ListEnabled(ctx context.Context, tenantID uint64) ([]*types.MCPService, error) {
+	return r.List(ctx, tenantID)
+}
+
+func (r *fakeMCPRepo) ListByIDs(_ context.Context, _ uint64, ids []string) ([]*types.MCPService, error) {
+	out := make([]*types.MCPService, 0, len(ids))
+	for _, id := range ids {
+		if s, ok := r.store[id]; ok {
+			out = append(out, cloneService(s))
+		}
+	}
+	return out, nil
+}
+
+func (r *fakeMCPRepo) Update(_ context.Context, s *types.MCPService) error {
+	r.store[s.ID] = s
+	return nil
+}
+
+func (r *fakeMCPRepo) Delete(_ context.Context, _ uint64, id string) error {
+	delete(r.store, id)
+	return nil
+}
+
+// seedService plants a service with the given auth credentials into the fake
+// repo and returns the service ID. Convenience helper used by every test.
+func seedService(t *testing.T, repo *fakeMCPRepo, apiKey, token string) string {
+	t.Helper()
+	s := &types.MCPService{
+		ID:            "svc-test",
+		TenantID:      1,
+		Name:          "test",
+		Enabled:       true,
+		TransportType: types.MCPTransportSSE,
+		AuthConfig: &types.MCPAuthConfig{
+			APIKey: apiKey,
+			Token:  token,
+		},
+	}
+	require.NoError(t, repo.Create(context.Background(), s))
+	return s.ID
+}
+
+// newTestService wires up a mcpServiceService with a fresh fake repo and a
+// real (empty) MCPManager. CloseClient on an empty manager is a no-op, so
+// tests can safely exercise the configChanged code paths.
+func newTestService() (*mcpServiceService, *fakeMCPRepo) {
+	repo := newFakeMCPRepo()
+	svc := &mcpServiceService{
+		mcpServiceRepo: repo,
+		mcpManager:     mcp.NewMCPManager(),
+	}
+	return svc, repo
+}
+
+// buildFullUpdate returns an UpdateMCPService input that exercises the
+// "full update" branch (service.Name is non-empty), which is the branch that
+// actually merges AuthConfig.
+func buildFullUpdate(id string, auth *types.MCPAuthConfig) *types.MCPService {
+	return &types.MCPService{
+		ID:            id,
+		TenantID:      1,
+		Name:          "test", // non-empty → full update branch
+		Enabled:       true,
+		TransportType: types.MCPTransportSSE,
+		AuthConfig:    auth,
+	}
+}
+
+func TestUpdateMCPService_PreservesSecretsOnEmptyOrRedacted(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("nil AuthConfig preserves existing", func(t *testing.T) {
+		svc, repo := newTestService()
+		id := seedService(t, repo, "stored-api", "stored-token")
+
+		upd := buildFullUpdate(id, nil)
+		require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+		got := repo.store[id]
+		assert.Equal(t, "stored-api", got.AuthConfig.APIKey)
+		assert.Equal(t, "stored-token", got.AuthConfig.Token)
+	})
+
+	t.Run("empty string preserves existing", func(t *testing.T) {
+		svc, repo := newTestService()
+		id := seedService(t, repo, "stored-api", "stored-token")
+
+		upd := buildFullUpdate(id, &types.MCPAuthConfig{APIKey: "", Token: ""})
+		require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+		got := repo.store[id]
+		assert.Equal(t, "stored-api", got.AuthConfig.APIKey)
+		assert.Equal(t, "stored-token", got.AuthConfig.Token)
+	})
+
+	t.Run("redacted placeholder preserves existing (NELO-1299 round-trip)", func(t *testing.T) {
+		svc, repo := newTestService()
+		id := seedService(t, repo, "stored-api", "stored-token")
+
+		upd := buildFullUpdate(id, &types.MCPAuthConfig{
+			APIKey: types.RedactedSecretPlaceholder,
+			Token:  types.RedactedSecretPlaceholder,
+		})
+		require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+		got := repo.store[id]
+		assert.Equal(t, "stored-api", got.AuthConfig.APIKey)
+		assert.Equal(t, "stored-token", got.AuthConfig.Token)
+	})
+}
+
+func TestUpdateMCPService_ReplacesOnExplicitValue(t *testing.T) {
+	ctx := context.Background()
+	svc, repo := newTestService()
+	id := seedService(t, repo, "stored-api", "stored-token")
+
+	upd := buildFullUpdate(id, &types.MCPAuthConfig{
+		APIKey: "new-api",
+		Token:  "new-token",
+	})
+	require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+	got := repo.store[id]
+	assert.Equal(t, "new-api", got.AuthConfig.APIKey)
+	assert.Equal(t, "new-token", got.AuthConfig.Token)
+}
+
+func TestUpdateMCPService_MixedFields(t *testing.T) {
+	ctx := context.Background()
+	svc, repo := newTestService()
+	id := seedService(t, repo, "stored-api", "stored-token")
+
+	// Replace token only, leave api_key as redacted placeholder → preserve
+	upd := buildFullUpdate(id, &types.MCPAuthConfig{
+		APIKey: types.RedactedSecretPlaceholder,
+		Token:  "new-token",
+	})
+	require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+	got := repo.store[id]
+	assert.Equal(t, "stored-api", got.AuthConfig.APIKey, "api_key should be preserved")
+	assert.Equal(t, "new-token", got.AuthConfig.Token, "token should be replaced")
+}
+
+func TestUpdateMCPService_ClearFlags(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("ClearToken removes stored token, preserves api_key", func(t *testing.T) {
+		svc, repo := newTestService()
+		id := seedService(t, repo, "stored-api", "stored-token")
+
+		upd := buildFullUpdate(id, &types.MCPAuthConfig{
+			APIKey:     types.RedactedSecretPlaceholder,
+			ClearToken: true,
+		})
+		require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+		got := repo.store[id]
+		assert.Equal(t, "stored-api", got.AuthConfig.APIKey)
+		assert.Empty(t, got.AuthConfig.Token)
+	})
+
+	t.Run("ClearAPIKey removes stored api_key, preserves token", func(t *testing.T) {
+		svc, repo := newTestService()
+		id := seedService(t, repo, "stored-api", "stored-token")
+
+		upd := buildFullUpdate(id, &types.MCPAuthConfig{
+			ClearAPIKey: true,
+			Token:       types.RedactedSecretPlaceholder,
+		})
+		require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+		got := repo.store[id]
+		assert.Empty(t, got.AuthConfig.APIKey)
+		assert.Equal(t, "stored-token", got.AuthConfig.Token)
+	})
+
+	t.Run("ClearToken takes precedence over submitted value", func(t *testing.T) {
+		svc, repo := newTestService()
+		id := seedService(t, repo, "stored-api", "stored-token")
+
+		upd := buildFullUpdate(id, &types.MCPAuthConfig{
+			Token:      "will-be-ignored",
+			ClearToken: true,
+		})
+		require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+		got := repo.store[id]
+		assert.Empty(t, got.AuthConfig.Token)
+	})
+
+	t.Run("clear flags are not persisted", func(t *testing.T) {
+		svc, repo := newTestService()
+		id := seedService(t, repo, "stored-api", "stored-token")
+
+		upd := buildFullUpdate(id, &types.MCPAuthConfig{ClearToken: true})
+		require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+		got := repo.store[id]
+		require.NotNil(t, got.AuthConfig)
+		assert.False(t, got.AuthConfig.ClearToken, "ClearToken must not be persisted")
+		assert.False(t, got.AuthConfig.ClearAPIKey, "ClearAPIKey must not be persisted")
+	})
+
+	t.Run("clear on already-empty field is a no-op", func(t *testing.T) {
+		svc, repo := newTestService()
+		id := seedService(t, repo, "stored-api", "") // token not set
+
+		upd := buildFullUpdate(id, &types.MCPAuthConfig{ClearToken: true})
+		require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+		got := repo.store[id]
+		assert.Equal(t, "stored-api", got.AuthConfig.APIKey)
+		assert.Empty(t, got.AuthConfig.Token)
+	})
+}
+
+func TestListMCPServices_RedactsSecrets(t *testing.T) {
+	ctx := context.Background()
+	svc, repo := newTestService()
+	seedService(t, repo, "real-api", "real-token")
+
+	got, err := svc.ListMCPServices(ctx, 1)
+	require.NoError(t, err)
+	require.Len(t, got, 1)
+	assert.Equal(t, types.RedactedSecretPlaceholder, got[0].AuthConfig.APIKey)
+	assert.Equal(t, types.RedactedSecretPlaceholder, got[0].AuthConfig.Token)
+
+	// And the underlying store is untouched
+	stored := repo.store["svc-test"]
+	assert.Equal(t, "real-api", stored.AuthConfig.APIKey)
+	assert.Equal(t, "real-token", stored.AuthConfig.Token)
+}
+
+func TestGetMCPServiceByID_RedactsSecrets(t *testing.T) {
+	ctx := context.Background()
+	svc, repo := newTestService()
+	id := seedService(t, repo, "real-api", "real-token")
+
+	got, err := svc.GetMCPServiceByID(ctx, 1, id)
+	require.NoError(t, err)
+	require.NotNil(t, got.AuthConfig)
+	assert.Equal(t, types.RedactedSecretPlaceholder, got.AuthConfig.APIKey)
+	assert.Equal(t, types.RedactedSecretPlaceholder, got.AuthConfig.Token)
+
+	// underlying store unchanged
+	stored := repo.store[id]
+	assert.Equal(t, "real-api", stored.AuthConfig.APIKey)
+	assert.Equal(t, "real-token", stored.AuthConfig.Token)
+}
+
+func TestGetMCPServiceByID_EmptySecretsStayEmpty(t *testing.T) {
+	ctx := context.Background()
+	svc, repo := newTestService()
+	id := seedService(t, repo, "", "") // both empty
+
+	got, err := svc.GetMCPServiceByID(ctx, 1, id)
+	require.NoError(t, err)
+	require.NotNil(t, got.AuthConfig)
+	assert.Empty(t, got.AuthConfig.APIKey, "empty secret must stay empty, not be redacted")
+	assert.Empty(t, got.AuthConfig.Token)
+}
+
+// Partial update: service.Name == "" is interpreted as "only touch enabled".
+// A clear flag sent in such a body was previously dropped; the refactor now
+// merges AuthConfig unconditionally so single-field clears round-trip.
+func TestUpdateMCPService_PartialUpdateHonorsClearFlag(t *testing.T) {
+	ctx := context.Background()
+	svc, repo := newTestService()
+	id := seedService(t, repo, "stored-api", "stored-token")
+
+	// Partial update body: no name, enabled flipped, ClearToken set.
+	upd := &types.MCPService{
+		ID:       id,
+		TenantID: 1,
+		Enabled:  true, // keep enabled, but simulate a "flag only" request
+		AuthConfig: &types.MCPAuthConfig{
+			ClearToken: true,
+		},
+	}
+	require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+	got := repo.store[id]
+	assert.Equal(t, "stored-api", got.AuthConfig.APIKey, "APIKey preserved in partial update")
+	assert.Empty(t, got.AuthConfig.Token, "ClearToken must clear Token even in partial update")
+}
+
+// CustomHeaders: nil means "no change" (preserve existing). Sending a
+// non-nil (including empty) map replaces. Previously the merge always
+// overwrote, silently wiping headers on any auth_config-bearing request.
+func TestUpdateMCPService_CustomHeadersPreserveOnNil(t *testing.T) {
+	ctx := context.Background()
+	svc, repo := newTestService()
+	id := seedService(t, repo, "stored-api", "stored-token")
+	// Seed with custom headers.
+	repo.store[id].AuthConfig.CustomHeaders = map[string]string{"X-Tenant": "acme"}
+
+	// Update with AuthConfig but nil CustomHeaders → preserve.
+	upd := buildFullUpdate(id, &types.MCPAuthConfig{
+		Token: "new-token",
+	})
+	require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+	got := repo.store[id]
+	assert.Equal(t, "acme", got.AuthConfig.CustomHeaders["X-Tenant"],
+		"nil CustomHeaders in request must preserve existing headers")
+}
+
+func TestUpdateMCPService_CustomHeadersReplaceOnNonNil(t *testing.T) {
+	ctx := context.Background()
+	svc, repo := newTestService()
+	id := seedService(t, repo, "stored-api", "stored-token")
+	repo.store[id].AuthConfig.CustomHeaders = map[string]string{"X-Tenant": "acme"}
+
+	upd := buildFullUpdate(id, &types.MCPAuthConfig{
+		APIKey:        types.RedactedSecretPlaceholder,
+		Token:         types.RedactedSecretPlaceholder,
+		CustomHeaders: map[string]string{"X-Replaced": "yes"},
+	})
+	require.NoError(t, svc.UpdateMCPService(ctx, upd))
+
+	got := repo.store[id]
+	assert.Equal(t, map[string]string{"X-Replaced": "yes"}, got.AuthConfig.CustomHeaders,
+		"non-nil CustomHeaders must replace the stored map")
+}
diff --git a/internal/handler/datasource.go b/internal/handler/datasource.go
index aea81fc3..61497d51 100644
--- a/internal/handler/datasource.go
+++ b/internal/handler/datasource.go
@@ -114,6 +114,7 @@ func (h *DataSourceHandler) CreateDataSource(c *gin.Context) {
 		return
 	}
 
+	ds.RedactSensitiveData()
 	c.JSON(http.StatusCreated, ds)
 }
 
@@ -142,6 +143,7 @@ func (h *DataSourceHandler) GetDataSource(c *gin.Context) {
 		return
 	}
 
+	ds.RedactSensitiveData()
 	c.JSON(http.StatusOK, ds)
 }
 
@@ -179,6 +181,9 @@ func (h *DataSourceHandler) ListDataSources(c *gin.Context) {
 	if dataSources == nil {
 		dataSources = make([]*types.DataSource, 0)
 	}
+	for _, ds := range dataSources {
+		ds.RedactSensitiveData()
+	}
 	c.JSON(http.StatusOK, dataSources)
 }
 
@@ -224,6 +229,7 @@ func (h *DataSourceHandler) UpdateDataSource(c *gin.Context) {
 		return
 	}
 
+	ds.RedactSensitiveData()
 	c.JSON(http.StatusOK, ds)
 }
 
diff --git a/internal/handler/mcp_service.go b/internal/handler/mcp_service.go
index dad4200e..f1b6ecf4 100644
--- a/internal/handler/mcp_service.go
+++ b/internal/handler/mcp_service.go
@@ -81,6 +81,9 @@ func (h *MCPServiceHandler) CreateMCPService(c *gin.Context) {
 		return
 	}
 
+	// Redact before echoing so the Create response honors the same
+	// "secrets never leave the server" invariant as List/Get/Update.
+	service.RedactSensitiveData()
 	c.JSON(http.StatusOK, gin.H{
 		"success": true,
 		"data":    service,
@@ -278,6 +281,29 @@ func (h *MCPServiceHandler) UpdateMCPService(c *gin.Context) {
 		if token, ok := authConfig["token"].(string); ok {
 			service.AuthConfig.Token = token
 		}
+		// Write-only clear flags — must be explicitly pulled off the map
+		// since this handler intentionally uses a manual map-to-struct
+		// projection to support partial updates (see "Use map to handle
+		// partial updates" comment above). A struct-based bind would have
+		// picked these up automatically.
+		if clearAPIKey, ok := authConfig["clear_api_key"].(bool); ok {
+			service.AuthConfig.ClearAPIKey = clearAPIKey
+		}
+		if clearToken, ok := authConfig["clear_token"].(bool); ok {
+			service.AuthConfig.ClearToken = clearToken
+		}
+		// CustomHeaders — nil preserves, non-nil replaces (see
+		// MCPAuthConfig.MergeUpdate). Only copy when the key is present so
+		// the preserve-on-nil branch is reachable.
+		if customHeaders, ok := authConfig["custom_headers"].(map[string]interface{}); ok {
+			headers := make(map[string]string, len(customHeaders))
+			for k, v := range customHeaders {
+				if s, ok := v.(string); ok {
+					headers[k] = s
+				}
+			}
+			service.AuthConfig.CustomHeaders = headers
+		}
 	}
 	if advancedConfig, ok := updateData["advanced_config"].(map[string]interface{}); ok {
 		service.AdvancedConfig = &types.MCPAdvancedConfig{}
@@ -299,6 +325,10 @@ func (h *MCPServiceHandler) UpdateMCPService(c *gin.Context) {
 	}
 
 	logger.Infof(ctx, "MCP service updated successfully: %s", secutils.SanitizeForLog(serviceID))
+	// Redact before echoing so the Update response honors the same
+	// "secrets never leave the server" invariant as List/Get/Create, and so
+	// write-only Clear* flags from the request body are never echoed back.
+	service.RedactSensitiveData()
 	c.JSON(http.StatusOK, gin.H{
 		"success": true,
 		"data":    service,
diff --git a/internal/handler/model.go b/internal/handler/model.go
index f2497f30..fdfb86a6 100644
--- a/internal/handler/model.go
+++ b/internal/handler/model.go
@@ -30,34 +30,54 @@ func NewModelHandler(service interfaces.ModelService) *ModelHandler {
 	return &ModelHandler{service: service}
 }
 
-// hideSensitiveInfo hides sensitive information (APIKey, BaseURL) for builtin models
-// Returns a copy of the model with sensitive fields cleared if it's a builtin model
+// hideSensitiveInfo prepares a Model for inclusion in a response body.
+//
+// For builtin models, APIKey and BaseURL are stripped entirely and only the
+// non-credential fields (embedding dimensions, parameter size) survive on a
+// fresh copy — builtin models are shared across tenants and must never leak
+// their underlying provider configuration.
+//
+// For tenant-owned models the sensitive fields (APIKey, AppSecret) are
+// replaced by the shared RedactedSecretPlaceholder via RedactSensitiveData,
+// on a copy so the in-memory representation stays usable by subsequent
+// code paths. Empty values stay empty so the frontend can render "set vs
+// not set" without guesswork.
 func hideSensitiveInfo(model *types.Model) *types.Model {
-	if !model.IsBuiltin {
-		return model
-	}
-
-	// Create a copy with sensitive information hidden
-	return &types.Model{
-		ID:          model.ID,
-		TenantID:    model.TenantID,
-		Name:        model.Name,
-		Type:        model.Type,
-		Source:      model.Source,
-		Description: model.Description,
-		Parameters: types.ModelParameters{
-			// Hide APIKey and BaseURL for builtin models
-			BaseURL: "",
-			APIKey:  "",
-			// Keep other parameters like embedding dimensions
-			EmbeddingParameters: model.Parameters.EmbeddingParameters,
-			ParameterSize:       model.Parameters.ParameterSize,
-		},
-		IsBuiltin: model.IsBuiltin,
-		Status:    model.Status,
-		CreatedAt: model.CreatedAt,
-		UpdatedAt: model.UpdatedAt,
+	if model.IsBuiltin {
+		return &types.Model{
+			ID:          model.ID,
+			TenantID:    model.TenantID,
+			Name:        model.Name,
+			Type:        model.Type,
+			Source:      model.Source,
+			Description: model.Description,
+			Parameters: types.ModelParameters{
+				// Hide APIKey and BaseURL for builtin models.
+				BaseURL: "",
+				APIKey:  "",
+				// Preserve non-credential fields so the frontend can still
+				// render correct capability metadata (vision support, Ollama
+				// parameter size, interface type, provider identifier, and
+				// any embedding dimensions). These were previously zeroed
+				// out, which caused builtin chat cards to look like their
+				// multimodal / provider metadata was unset.
+				EmbeddingParameters: model.Parameters.EmbeddingParameters,
+				ParameterSize:       model.Parameters.ParameterSize,
+				InterfaceType:       model.Parameters.InterfaceType,
+				Provider:            model.Parameters.Provider,
+				ExtraConfig:         model.Parameters.ExtraConfig,
+				SupportsVision:      model.Parameters.SupportsVision,
+			},
+			IsBuiltin: model.IsBuiltin,
+			Status:    model.Status,
+			CreatedAt: model.CreatedAt,
+			UpdatedAt: model.UpdatedAt,
+		}
 	}
+	// Tenant-owned model: redact secrets on a copy, preserving everything else.
+	cp := *model
+	cp.RedactSensitiveData()
+	return &cp
 }
 
 // CreateModelRequest defines the structure for model creation requests
@@ -310,12 +330,22 @@ func (h *ModelHandler) UpdateModel(c *gin.Context) {
 			return
 		}
 	}
-	// Preserve backend-managed fields not sent by frontend
-	req.Parameters.ParameterSize = model.Parameters.ParameterSize
-	if req.Parameters.ExtraConfig == nil {
-		req.Parameters.ExtraConfig = model.Parameters.ExtraConfig
+	// Apply write-only secret merge semantics before overwriting the stored
+	// parameters: empty or redacted APIKey/AppSecret preserves the stored
+	// value, the respective ClearXxx flag wipes it, any other value replaces.
+	merged := req.Parameters.MergeUpdate(model.Parameters)
+	// Preserve backend-managed fields not sent by frontend.
+	merged.ParameterSize = model.Parameters.ParameterSize
+	if merged.ExtraConfig == nil {
+		merged.ExtraConfig = model.Parameters.ExtraConfig
 	}
-	model.Parameters = req.Parameters
+	if req.Parameters.ClearAPIKey {
+		logger.Infof(ctx, "Model API key cleared by user: id=%s", id)
+	}
+	if req.Parameters.ClearAppSecret {
+		logger.Infof(ctx, "Model app_secret cleared by user: id=%s", id)
+	}
+	model.Parameters = merged
 
 	model.Source = req.Source
 	model.Type = req.Type
diff --git a/internal/handler/web_search_provider.go b/internal/handler/web_search_provider.go
index 76b10f0b..94c68969 100644
--- a/internal/handler/web_search_provider.go
+++ b/internal/handler/web_search_provider.go
@@ -108,6 +108,7 @@ func (h *WebSearchProviderHandler) CreateProvider(c *gin.Context) {
 		return
 	}
 
+	provider.RedactSensitiveData()
 	c.JSON(http.StatusCreated, gin.H{
 		"success": true,
 		"data":    provider,
@@ -131,6 +132,9 @@ func (h *WebSearchProviderHandler) ListProviders(c *gin.Context) {
 		return
 	}
 
+	for _, p := range providers {
+		p.RedactSensitiveData()
+	}
 	c.JSON(http.StatusOK, gin.H{
 		"success": true,
 		"data":    providers,
@@ -166,6 +170,7 @@ func (h *WebSearchProviderHandler) GetProvider(c *gin.Context) {
 		return
 	}
 
+	provider.RedactSensitiveData()
 	c.JSON(http.StatusOK, gin.H{
 		"success": true,
 		"data":    provider,
@@ -212,14 +217,37 @@ func (h *WebSearchProviderHandler) UpdateProvider(c *gin.Context) {
 		return
 	}
 
+	// Merge incoming parameters into the existing ones using write-only
+	// secret semantics: empty / redacted APIKey preserves the stored value,
+	// ClearAPIKey explicitly wipes it, any other value replaces. Non-secret
+	// fields flow through from the request directly.
+	mergedParams := req.Parameters.MergeUpdate(existing.Parameters)
+	if req.Parameters.ClearAPIKey {
+		logger.Infof(ctx, "WebSearchProvider API key cleared by user: id=%s",
+			secutils.SanitizeForLog(id))
+	}
+
+	// Preserve existing values for top-level metadata fields when the
+	// request omits them (empty string from the JSON decoder). Without this,
+	// a partial update that only flips IsDefault would clobber Name and
+	// Description on the stored record.
+	mergedName := req.Name
+	if mergedName == "" {
+		mergedName = existing.Name
+	}
+	mergedDescription := req.Description
+	if mergedDescription == "" {
+		mergedDescription = existing.Description
+	}
+
 	// Build updated entity, keeping immutable fields from existing
 	provider := &types.WebSearchProviderEntity{
 		ID:          id,
 		TenantID:    tenantID,
-		Name:        secutils.SanitizeForLog(req.Name),
+		Name:        secutils.SanitizeForLog(mergedName),
 		Provider:    existing.Provider, // Provider type is immutable after creation
-		Description: secutils.SanitizeForLog(req.Description),
-		Parameters:  req.Parameters,
+		Description: secutils.SanitizeForLog(mergedDescription),
+		Parameters:  mergedParams,
 		IsDefault:   req.IsDefault,
 	}
 
@@ -232,6 +260,7 @@ func (h *WebSearchProviderHandler) UpdateProvider(c *gin.Context) {
 	// Re-fetch to get the full stored state
 	updated, _ := h.repo.GetByID(ctx, tenantID, id)
 	if updated != nil {
+		updated.RedactSensitiveData()
 		c.JSON(http.StatusOK, gin.H{"success": true, "data": updated})
 	} else {
 		c.JSON(http.StatusOK, gin.H{"success": true})
@@ -371,8 +400,17 @@ func (h *WebSearchProviderHandler) TestProviderRaw(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"success": true})
 }
 
-// doTestSearch creates a temporary provider and runs a simple test query
+// doTestSearch creates a temporary provider and runs a simple test query.
+//
+// The provider would otherwise try to authenticate against the upstream API
+// with the redacted placeholder (which is guaranteed to fail with a
+// confusing error). Reject it up front with an actionable message so the
+// user knows they should type a real key or test against the saved config
+// via /test instead.
 func (h *WebSearchProviderHandler) doTestSearch(ctx context.Context, providerType string, params types.WebSearchProviderParameters) error {
+	if params.APIKey == types.RedactedSecretPlaceholder {
+		return fmt.Errorf("api_key looks like the redacted placeholder; enter your real key or call POST /api/v1/web-search-providers/{id}/test to exercise the saved credential")
+	}
 	logger.Infof(ctx, "[WebSearch][Test] testing provider type=%s", providerType)
 	searchProvider, err := h.registry.CreateProvider(providerType, params)
 	if err != nil {
diff --git a/internal/types/datasource.go b/internal/types/datasource.go
index dec6bc14..cf2a431e 100644
--- a/internal/types/datasource.go
+++ b/internal/types/datasource.go
@@ -194,7 +194,15 @@ func (s *SyncLog) BeforeCreate(tx *gorm.DB) error {
 }
 
 // DataSourceConfig represents the unencrypted configuration structure
-// Each connector type will have its own specific fields
+// Each connector type will have its own specific fields.
+//
+// ClearCredentials is a write-only flag used in Update requests to
+// explicitly remove the stored credential map. Because credentials are
+// per-connector atomic sets (e.g. an OAuth token pair, a GitHub PAT, a
+// Confluence API token), individual-field removal is intentionally not
+// supported — revoking one field in isolation would leave the connector in
+// a broken half-configured state. The flag is never persisted to storage
+// and never surfaces in responses (omitempty + zero value).
 type DataSourceConfig struct {
 	// Common fields applicable to most connectors
 	Type string `json:"type"`
@@ -207,6 +215,98 @@ type DataSourceConfig struct {
 
 	// Connector-specific configuration
 	Settings map[string]interface{} `json:"settings"`
+
+	// Write-only flag — request-only, never persisted or returned.
+	ClearCredentials bool `json:"clear_credentials,omitempty"`
+}
+
+// HasCredentials reports whether the credentials map carries any value at
+// all. Used by the Update path to detect the "Remove all credentials"
+// transition (existing.HasCredentials() && !merged.HasCredentials()) and
+// skip live-connector validation that would otherwise reject the wipe.
+func (d DataSourceConfig) HasCredentials() bool {
+	return len(d.Credentials) > 0
+}
+
+// Redacted returns a copy of the config with every string value in
+// Credentials replaced by RedactedSecretPlaceholder so it can be returned to
+// the client without exposing stored secrets. Empty string values stay empty
+// so the frontend can still distinguish "set (hidden)" from "not set" per
+// key. Non-string credential values (rare but possible for numeric IDs or
+// structured settings) pass through unchanged.
+//
+// Named "Redacted" rather than "RedactSensitiveData" because it returns a
+// copy instead of mutating in place, matching the naming convention of
+// ConnectionConfig.MaskSensitiveFields in types/vectorstore.go.
+func (d DataSourceConfig) Redacted() DataSourceConfig {
+	cp := d
+	// ClearCredentials is a request-only signal; never echo it in responses.
+	cp.ClearCredentials = false
+	if d.Credentials == nil {
+		return cp
+	}
+	redacted := make(map[string]interface{}, len(d.Credentials))
+	for k, v := range d.Credentials {
+		if s, ok := v.(string); ok && s != "" {
+			redacted[k] = RedactedSecretPlaceholder
+		} else {
+			redacted[k] = v
+		}
+	}
+	cp.Credentials = redacted
+	return cp
+}
+
+// MergeUpdate applies write-only secret merge semantics for Update requests.
+//
+//   - ClearCredentials=true → wipe the entire credentials map
+//   - Otherwise, each string credential key is merged individually using
+//     PreserveIfRedacted: empty or the redacted placeholder preserves the
+//     existing value, any other value replaces. Non-string credential
+//     values from incoming always overwrite (they aren't redacted either).
+//   - Non-secret fields (Type, ResourceIDs, Settings) flow from incoming
+//     directly.
+//   - The write-only ClearCredentials flag is cleared on the merged result.
+func (d DataSourceConfig) MergeUpdate(existing DataSourceConfig) DataSourceConfig {
+	merged := d
+	merged.ClearCredentials = false
+	if d.ClearCredentials {
+		merged.Credentials = nil
+		return merged
+	}
+
+	mergedCreds := make(map[string]interface{}, len(existing.Credentials)+len(d.Credentials))
+	for k, v := range existing.Credentials {
+		mergedCreds[k] = v
+	}
+	for k, v := range d.Credentials {
+		if s, ok := v.(string); ok {
+			if IsRedactedOrEmpty(s) {
+				continue // preserve existing value for this key
+			}
+		}
+		mergedCreds[k] = v
+	}
+	merged.Credentials = mergedCreds
+	return merged
+}
+
+// RedactSensitiveData parses the Config jsonb, redacts string values in the
+// Credentials map, and writes the result back. No-op when Config is empty or
+// fails to parse (the caller continues to return the DataSource with
+// whatever Config representation it has — better than dropping the response).
+func (d *DataSource) RedactSensitiveData() {
+	if len(d.Config) == 0 {
+		return
+	}
+	parsed, err := d.ParseConfig()
+	if err != nil || parsed == nil {
+		return
+	}
+	redacted := parsed.Redacted()
+	if blob, err := redacted.ToJSON(); err == nil {
+		d.Config = blob
+	}
 }
 
 // Resource represents a syncable resource (document, folder, space) from external system
diff --git a/internal/types/datasource_test.go b/internal/types/datasource_test.go
new file mode 100644
index 00000000..9e1d3348
--- /dev/null
+++ b/internal/types/datasource_test.go
@@ -0,0 +1,206 @@
+package types
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDataSourceConfig_Redacted(t *testing.T) {
+	t.Run("redacts all string values in Credentials", func(t *testing.T) {
+		cfg := DataSourceConfig{
+			Type: "github",
+			Credentials: map[string]interface{}{
+				"access_token": "real-pat",
+				"installation_id": "real-id",
+			},
+			ResourceIDs: []string{"repo-1"},
+		}
+		out := cfg.Redacted()
+		assert.Equal(t, RedactedSecretPlaceholder, out.Credentials["access_token"])
+		assert.Equal(t, RedactedSecretPlaceholder, out.Credentials["installation_id"])
+		assert.Equal(t, "github", out.Type, "non-credential fields preserved")
+		assert.Equal(t, []string{"repo-1"}, out.ResourceIDs)
+	})
+
+	t.Run("leaves empty string credentials empty", func(t *testing.T) {
+		cfg := DataSourceConfig{
+			Credentials: map[string]interface{}{"token": ""},
+		}
+		out := cfg.Redacted()
+		assert.Equal(t, "", out.Credentials["token"],
+			"empty must stay empty to signal 'not set' to the frontend")
+	})
+
+	t.Run("non-string credential values pass through unchanged", func(t *testing.T) {
+		cfg := DataSourceConfig{
+			Credentials: map[string]interface{}{
+				"token":          "secret",
+				"installation_id": float64(12345),
+				"metadata":       map[string]interface{}{"nested": "value"},
+			},
+		}
+		out := cfg.Redacted()
+		assert.Equal(t, RedactedSecretPlaceholder, out.Credentials["token"])
+		assert.Equal(t, float64(12345), out.Credentials["installation_id"])
+		assert.NotNil(t, out.Credentials["metadata"])
+	})
+
+	t.Run("does not mutate original", func(t *testing.T) {
+		cfg := DataSourceConfig{
+			Credentials: map[string]interface{}{"token": "secret"},
+		}
+		_ = cfg.Redacted()
+		assert.Equal(t, "secret", cfg.Credentials["token"])
+	})
+
+	t.Run("nil credentials map stays nil", func(t *testing.T) {
+		cfg := DataSourceConfig{Type: "github"}
+		out := cfg.Redacted()
+		assert.Nil(t, out.Credentials)
+	})
+
+	t.Run("ClearCredentials flag stripped from response", func(t *testing.T) {
+		cfg := DataSourceConfig{ClearCredentials: true, Type: "github"}
+		out := cfg.Redacted()
+		assert.False(t, out.ClearCredentials, "write-only flag must not echo back")
+	})
+}
+
+func TestDataSourceConfig_MergeUpdate(t *testing.T) {
+	existing := DataSourceConfig{
+		Type: "github",
+		Credentials: map[string]interface{}{
+			"access_token":   "stored-pat",
+			"installation_id": "stored-id",
+		},
+		ResourceIDs: []string{"old-repo"},
+	}
+
+	t.Run("empty credential value preserves existing", func(t *testing.T) {
+		in := DataSourceConfig{
+			Type: "github",
+			Credentials: map[string]interface{}{
+				"access_token": "",
+			},
+		}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-pat", out.Credentials["access_token"])
+		assert.Equal(t, "stored-id", out.Credentials["installation_id"],
+			"keys not present in incoming carry over from existing")
+	})
+
+	t.Run("redacted placeholder preserves existing", func(t *testing.T) {
+		in := DataSourceConfig{
+			Credentials: map[string]interface{}{
+				"access_token": RedactedSecretPlaceholder,
+			},
+		}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-pat", out.Credentials["access_token"])
+	})
+
+	t.Run("real value replaces existing", func(t *testing.T) {
+		in := DataSourceConfig{
+			Credentials: map[string]interface{}{
+				"access_token": "new-pat",
+			},
+		}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "new-pat", out.Credentials["access_token"])
+		assert.Equal(t, "stored-id", out.Credentials["installation_id"],
+			"other keys preserved from existing")
+	})
+
+	t.Run("mixed preserve and replace", func(t *testing.T) {
+		in := DataSourceConfig{
+			Credentials: map[string]interface{}{
+				"access_token":   RedactedSecretPlaceholder, // preserve
+				"installation_id": "new-id",                 // replace
+			},
+		}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-pat", out.Credentials["access_token"])
+		assert.Equal(t, "new-id", out.Credentials["installation_id"])
+	})
+
+	t.Run("ClearCredentials wipes entire map", func(t *testing.T) {
+		in := DataSourceConfig{ClearCredentials: true}
+		out := in.MergeUpdate(existing)
+		assert.Nil(t, out.Credentials,
+			"ClearCredentials removes all credential keys atomically")
+	})
+
+	t.Run("ClearCredentials takes precedence over submitted values", func(t *testing.T) {
+		in := DataSourceConfig{
+			ClearCredentials: true,
+			Credentials: map[string]interface{}{
+				"access_token": "will-be-ignored",
+			},
+		}
+		out := in.MergeUpdate(existing)
+		assert.Nil(t, out.Credentials)
+	})
+
+	t.Run("ClearCredentials flag never persists on merged result", func(t *testing.T) {
+		in := DataSourceConfig{ClearCredentials: true}
+		out := in.MergeUpdate(existing)
+		assert.False(t, out.ClearCredentials, "write-only flag must not leak to storage")
+	})
+
+	t.Run("non-string incoming values always overwrite", func(t *testing.T) {
+		in := DataSourceConfig{
+			Credentials: map[string]interface{}{
+				"installation_id": float64(999),
+			},
+		}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, float64(999), out.Credentials["installation_id"],
+			"non-string values are never treated as redacted/empty")
+	})
+
+	t.Run("non-credential fields flow from incoming", func(t *testing.T) {
+		in := DataSourceConfig{
+			Type:        "notion",
+			ResourceIDs: []string{"new-repo"},
+		}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "notion", out.Type)
+		assert.Equal(t, []string{"new-repo"}, out.ResourceIDs)
+	})
+}
+
+func TestDataSource_RedactSensitiveData(t *testing.T) {
+	t.Run("redacts string credentials in Config jsonb", func(t *testing.T) {
+		cfg := DataSourceConfig{
+			Type: "github",
+			Credentials: map[string]interface{}{
+				"access_token": "real-pat",
+			},
+		}
+		blob, err := json.Marshal(cfg)
+		require.NoError(t, err)
+
+		ds := &DataSource{Config: JSON(blob)}
+		ds.RedactSensitiveData()
+
+		parsed, err := ds.ParseConfig()
+		require.NoError(t, err)
+		assert.Equal(t, RedactedSecretPlaceholder, parsed.Credentials["access_token"])
+	})
+
+	t.Run("no-op on empty config", func(t *testing.T) {
+		ds := &DataSource{Config: nil}
+		ds.RedactSensitiveData() // must not panic
+		assert.Nil(t, ds.Config)
+	})
+
+	t.Run("no-op on malformed config", func(t *testing.T) {
+		ds := &DataSource{Config: JSON(`not valid json`)}
+		ds.RedactSensitiveData() // must not panic
+		// Config remains unchanged — better than dropping the response.
+		assert.Equal(t, JSON(`not valid json`), ds.Config)
+	})
+}
diff --git a/internal/types/mcp.go b/internal/types/mcp.go
index 00568bff..a4029357 100644
--- a/internal/types/mcp.go
+++ b/internal/types/mcp.go
@@ -41,11 +41,60 @@ type MCPService struct {
 // MCPHeaders represents HTTP headers as a map
 type MCPHeaders map[string]string
 
-// MCPAuthConfig represents authentication configuration for MCP service
+// MCPAuthConfig represents authentication configuration for MCP service.
+//
+// ClearAPIKey and ClearToken are write-only flags used in Update requests to
+// explicitly remove a stored credential. They are not persisted (gorm:"-") and
+// never appear in responses (omitempty + zero value). Without these flags an
+// empty APIKey/Token submitted in an Update request is interpreted as "no
+// change", so this is the only way to intentionally clear a stored secret.
 type MCPAuthConfig struct {
 	APIKey        string            `json:"api_key,omitempty"`
 	Token         string            `json:"token,omitempty"`
 	CustomHeaders map[string]string `json:"custom_headers,omitempty"`
+
+	// Write-only clear flags.
+	ClearAPIKey bool `json:"clear_api_key,omitempty" gorm:"-"`
+	ClearToken  bool `json:"clear_token,omitempty"   gorm:"-"`
+}
+
+// MergeUpdate applies write-only secret merge semantics for Update requests.
+// The receiver is the incoming request DTO; existing is the currently stored
+// value (may be nil for new services).
+//
+// Behavior:
+//   - ClearAPIKey / ClearToken take precedence — wipe the corresponding field.
+//   - Otherwise APIKey / Token use PreserveIfRedacted: empty or the redacted
+//     placeholder preserves existing, any other value replaces.
+//   - CustomHeaders: nil (absent in request) preserves existing; any non-nil
+//     value (including an empty map) replaces. Callers that want to clear
+//     headers explicitly should send {} rather than omitting the field.
+//   - Write-only clear flags are cleared on the merged result so they never
+//     leak to storage.
+func (c *MCPAuthConfig) MergeUpdate(existing *MCPAuthConfig) *MCPAuthConfig {
+	merged := &MCPAuthConfig{}
+	if existing != nil {
+		*merged = *existing
+		merged.ClearAPIKey = false
+		merged.ClearToken = false
+	}
+	if c == nil {
+		return merged
+	}
+	if c.ClearAPIKey {
+		merged.APIKey = ""
+	} else {
+		merged.APIKey = PreserveIfRedacted(c.APIKey, merged.APIKey)
+	}
+	if c.ClearToken {
+		merged.Token = ""
+	} else {
+		merged.Token = PreserveIfRedacted(c.Token, merged.Token)
+	}
+	if c.CustomHeaders != nil {
+		merged.CustomHeaders = c.CustomHeaders
+	}
+	return merged
 }
 
 // MCPAdvancedConfig represents advanced configuration for MCP service
@@ -228,16 +277,30 @@ func GetDefaultAdvancedConfig() *MCPAdvancedConfig {
 	}
 }
 
-// MaskSensitiveData masks sensitive information in the MCP service for display
-func (m *MCPService) MaskSensitiveData() {
-	if m.AuthConfig != nil {
-		if m.AuthConfig.APIKey != "" {
-			m.AuthConfig.APIKey = maskString(m.AuthConfig.APIKey)
-		}
-		if m.AuthConfig.Token != "" {
-			m.AuthConfig.Token = maskString(m.AuthConfig.Token)
-		}
+// RedactSensitiveData replaces secret values in the MCP service with
+// RedactedSecretPlaceholder while preserving the "set vs not set" distinction
+// (empty values stay empty). Mutates the receiver in place; callers that need
+// to retain the originals should pass a copy.
+//
+// This replaces the previous MaskSensitiveData implementation which returned
+// a "first4****last4" slice of the original secret, leaking 8 characters of
+// entropy per value. The new implementation returns a fixed placeholder with
+// no information about the underlying secret.
+func (m *MCPService) RedactSensitiveData() {
+	if m.AuthConfig == nil {
+		return
 	}
+	if m.AuthConfig.APIKey != "" {
+		m.AuthConfig.APIKey = RedactedSecretPlaceholder
+	}
+	if m.AuthConfig.Token != "" {
+		m.AuthConfig.Token = RedactedSecretPlaceholder
+	}
+	// Write-only flags must never reach the client. omitempty alone is
+	// insufficient because a true value serializes; explicitly clear them so
+	// any response path that runs RedactSensitiveData is safe by construction.
+	m.AuthConfig.ClearAPIKey = false
+	m.AuthConfig.ClearToken = false
 }
 
 // HideSensitiveInfo returns a copy of the MCP service with sensitive fields cleared for builtin services
@@ -255,10 +318,3 @@ func (m *MCPService) HideSensitiveInfo() *MCPService {
 	return &copy
 }
 
-// maskString masks a string, showing only first 4 and last 4 characters
-func maskString(s string) string {
-	if len(s) <= 8 {
-		return "****"
-	}
-	return s[:4] + "****" + s[len(s)-4:]
-}
diff --git a/internal/types/mcp_test.go b/internal/types/mcp_test.go
new file mode 100644
index 00000000..e932df96
--- /dev/null
+++ b/internal/types/mcp_test.go
@@ -0,0 +1,52 @@
+package types
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMCPService_RedactSensitiveData(t *testing.T) {
+	t.Run("redacts both api_key and token when set", func(t *testing.T) {
+		m := &MCPService{
+			AuthConfig: &MCPAuthConfig{
+				APIKey: "real-api",
+				Token:  "real-token",
+			},
+		}
+		m.RedactSensitiveData()
+		assert.Equal(t, RedactedSecretPlaceholder, m.AuthConfig.APIKey)
+		assert.Equal(t, RedactedSecretPlaceholder, m.AuthConfig.Token)
+	})
+
+	t.Run("leaves empty secrets empty", func(t *testing.T) {
+		m := &MCPService{AuthConfig: &MCPAuthConfig{}}
+		m.RedactSensitiveData()
+		assert.Empty(t, m.AuthConfig.APIKey, "empty must stay empty to signal 'not set' to the frontend")
+		assert.Empty(t, m.AuthConfig.Token)
+	})
+
+	t.Run("noop on nil AuthConfig", func(t *testing.T) {
+		m := &MCPService{AuthConfig: nil}
+		assert.NotPanics(t, func() { m.RedactSensitiveData() })
+		assert.Nil(t, m.AuthConfig)
+	})
+
+	t.Run("zeroes write-only clear flags so they never echo back", func(t *testing.T) {
+		// Regression for response-side leak: a true Clear* bool serializes
+		// despite json:"...,omitempty" because true is not a zero value.
+		// Any response path that runs RedactSensitiveData must produce JSON
+		// without the clear_api_key / clear_token keys.
+		m := &MCPService{
+			AuthConfig: &MCPAuthConfig{
+				APIKey:      "real-api",
+				Token:       "real-token",
+				ClearAPIKey: true,
+				ClearToken:  true,
+			},
+		}
+		m.RedactSensitiveData()
+		assert.False(t, m.AuthConfig.ClearAPIKey, "ClearAPIKey must be reset before response")
+		assert.False(t, m.AuthConfig.ClearToken, "ClearToken must be reset before response")
+	})
+}
diff --git a/internal/types/model.go b/internal/types/model.go
index 30748551..131e6726 100644
--- a/internal/types/model.go
+++ b/internal/types/model.go
@@ -77,6 +77,57 @@ type ModelParameters struct {
 	// WeKnoraCloud 厂商专用凭证
 	AppID     string `yaml:"app_id,omitempty"     json:"app_id,omitempty"`
 	AppSecret string `yaml:"app_secret,omitempty" json:"app_secret,omitempty"` // AES-256 加密存储，实际承载上游 API Key
+
+	// Write-only flags: set to true in Update requests to explicitly remove
+	// the corresponding credential. Never persisted (gorm:"-"), never
+	// returned in responses (omitempty + zero value).
+	ClearAPIKey    bool `yaml:"-" json:"clear_api_key,omitempty"    gorm:"-"`
+	ClearAppSecret bool `yaml:"-" json:"clear_app_secret,omitempty" gorm:"-"`
+}
+
+// RedactSensitiveData replaces secret values (APIKey, AppSecret) in
+// ModelParameters with RedactedSecretPlaceholder when set. Empty values stay
+// empty so the frontend can distinguish "set (hidden)" from "not set".
+// Mutates the receiver in place.
+func (m *Model) RedactSensitiveData() {
+	if m.Parameters.APIKey != "" {
+		m.Parameters.APIKey = RedactedSecretPlaceholder
+	}
+	if m.Parameters.AppSecret != "" {
+		m.Parameters.AppSecret = RedactedSecretPlaceholder
+	}
+	// Write-only flags must never reach the client. omitempty alone is
+	// insufficient because a true value serializes; explicitly clear them so
+	// any response path that runs RedactSensitiveData is safe by construction.
+	m.Parameters.ClearAPIKey = false
+	m.Parameters.ClearAppSecret = false
+}
+
+// MergeUpdate applies write-only secret merge semantics for Update requests:
+//
+//   - ClearAPIKey / ClearAppSecret take precedence — when true, the
+//     corresponding field becomes empty
+//   - Otherwise APIKey and AppSecret use PreserveIfRedacted: empty or the
+//     redacted placeholder preserves the existing value, any other value
+//     replaces
+//   - Non-secret fields flow from incoming directly
+//   - Write-only clear flags are cleared on the merged result so they never
+//     leak to storage
+func (p ModelParameters) MergeUpdate(existing ModelParameters) ModelParameters {
+	merged := p
+	if p.ClearAPIKey {
+		merged.APIKey = ""
+	} else {
+		merged.APIKey = PreserveIfRedacted(p.APIKey, existing.APIKey)
+	}
+	if p.ClearAppSecret {
+		merged.AppSecret = ""
+	} else {
+		merged.AppSecret = PreserveIfRedacted(p.AppSecret, existing.AppSecret)
+	}
+	merged.ClearAPIKey = false
+	merged.ClearAppSecret = false
+	return merged
 }
 
 // Model represents the AI model
diff --git a/internal/types/model_test.go b/internal/types/model_test.go
new file mode 100644
index 00000000..b344ae23
--- /dev/null
+++ b/internal/types/model_test.go
@@ -0,0 +1,139 @@
+package types
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestModel_RedactSensitiveData(t *testing.T) {
+	t.Run("redacts both APIKey and AppSecret when set", func(t *testing.T) {
+		m := &Model{
+			Parameters: ModelParameters{
+				APIKey:    "real-api",
+				AppSecret: "real-secret",
+				BaseURL:   "https://example.com",
+			},
+		}
+		m.RedactSensitiveData()
+		assert.Equal(t, RedactedSecretPlaceholder, m.Parameters.APIKey)
+		assert.Equal(t, RedactedSecretPlaceholder, m.Parameters.AppSecret)
+		assert.Equal(t, "https://example.com", m.Parameters.BaseURL,
+			"non-secret fields must be preserved")
+	})
+
+	t.Run("leaves empty secrets empty", func(t *testing.T) {
+		m := &Model{
+			Parameters: ModelParameters{BaseURL: "https://example.com"},
+		}
+		m.RedactSensitiveData()
+		assert.Empty(t, m.Parameters.APIKey)
+		assert.Empty(t, m.Parameters.AppSecret)
+	})
+
+	t.Run("redacts only set secret when one is empty", func(t *testing.T) {
+		m := &Model{
+			Parameters: ModelParameters{APIKey: "real-api"}, // AppSecret empty
+		}
+		m.RedactSensitiveData()
+		assert.Equal(t, RedactedSecretPlaceholder, m.Parameters.APIKey)
+		assert.Empty(t, m.Parameters.AppSecret)
+	})
+
+	t.Run("zeroes write-only clear flags so they never echo back", func(t *testing.T) {
+		// Regression for response-side leak: a true Clear* bool serializes
+		// despite json:"...,omitempty" because true is not a zero value.
+		// Any response path that runs RedactSensitiveData must produce JSON
+		// without the clear_* keys.
+		m := &Model{
+			Parameters: ModelParameters{
+				APIKey:         "real-api",
+				ClearAPIKey:    true,
+				ClearAppSecret: true,
+			},
+		}
+		m.RedactSensitiveData()
+		assert.False(t, m.Parameters.ClearAPIKey, "ClearAPIKey must be reset before response")
+		assert.False(t, m.Parameters.ClearAppSecret, "ClearAppSecret must be reset before response")
+	})
+}
+
+func TestModelParameters_MergeUpdate(t *testing.T) {
+	existing := ModelParameters{
+		APIKey:    "stored-api",
+		AppSecret: "stored-secret",
+		BaseURL:   "https://stored.example.com",
+		Provider:  "openai",
+	}
+
+	t.Run("empty secrets preserve existing", func(t *testing.T) {
+		in := ModelParameters{BaseURL: "https://new.example.com"}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-api", out.APIKey)
+		assert.Equal(t, "stored-secret", out.AppSecret)
+		assert.Equal(t, "https://new.example.com", out.BaseURL,
+			"non-secret fields flow from incoming")
+	})
+
+	t.Run("redacted placeholders preserve existing", func(t *testing.T) {
+		in := ModelParameters{
+			APIKey:    RedactedSecretPlaceholder,
+			AppSecret: RedactedSecretPlaceholder,
+		}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-api", out.APIKey)
+		assert.Equal(t, "stored-secret", out.AppSecret)
+	})
+
+	t.Run("real values replace existing", func(t *testing.T) {
+		in := ModelParameters{APIKey: "new-api", AppSecret: "new-secret"}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "new-api", out.APIKey)
+		assert.Equal(t, "new-secret", out.AppSecret)
+	})
+
+	t.Run("mixed preserve and replace", func(t *testing.T) {
+		in := ModelParameters{
+			APIKey:    RedactedSecretPlaceholder, // preserve
+			AppSecret: "new-secret",              // replace
+		}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-api", out.APIKey)
+		assert.Equal(t, "new-secret", out.AppSecret)
+	})
+
+	t.Run("ClearAPIKey wipes only APIKey", func(t *testing.T) {
+		in := ModelParameters{ClearAPIKey: true}
+		out := in.MergeUpdate(existing)
+		assert.Empty(t, out.APIKey)
+		assert.Equal(t, "stored-secret", out.AppSecret,
+			"ClearAPIKey must not affect AppSecret")
+	})
+
+	t.Run("ClearAppSecret wipes only AppSecret", func(t *testing.T) {
+		in := ModelParameters{ClearAppSecret: true}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-api", out.APIKey)
+		assert.Empty(t, out.AppSecret)
+	})
+
+	t.Run("both clear flags wipe both secrets", func(t *testing.T) {
+		in := ModelParameters{ClearAPIKey: true, ClearAppSecret: true}
+		out := in.MergeUpdate(existing)
+		assert.Empty(t, out.APIKey)
+		assert.Empty(t, out.AppSecret)
+	})
+
+	t.Run("clear takes precedence over submitted value", func(t *testing.T) {
+		in := ModelParameters{APIKey: "will-be-ignored", ClearAPIKey: true}
+		out := in.MergeUpdate(existing)
+		assert.Empty(t, out.APIKey)
+	})
+
+	t.Run("clear flags never persist on merged result", func(t *testing.T) {
+		in := ModelParameters{ClearAPIKey: true, ClearAppSecret: true}
+		out := in.MergeUpdate(existing)
+		assert.False(t, out.ClearAPIKey, "write-only flag must not leak to storage")
+		assert.False(t, out.ClearAppSecret, "write-only flag must not leak to storage")
+	})
+}
diff --git a/internal/types/secret.go b/internal/types/secret.go
new file mode 100644
index 00000000..a87b4b33
--- /dev/null
+++ b/internal/types/secret.go
@@ -0,0 +1,56 @@
+// Package types — shared secret redaction helpers for the "write-only secrets"
+// pattern applied across MCP services, Models, WebSearch providers,
+// DataSources, and VectorStores.
+//
+// The contract is:
+//
+//   - API responses replace sensitive values with RedactedSecretPlaceholder
+//     when the value is set, and leave it as the empty string when it is not.
+//     Clients can therefore distinguish "set (hidden)" from "not set" without
+//     ever seeing the secret itself.
+//
+//   - API Update requests treat an absent field, the empty string, or the
+//     RedactedSecretPlaceholder as "no change requested" (preserve), and any
+//     other value as an explicit replacement.
+//
+//   - Explicit removal of a stored secret is expressed with a dedicated
+//     write-only boolean flag on the request DTO (e.g. ClearAPIKey) rather
+//     than by sending an empty string, because the empty string is already
+//     reserved for "preserve".
+package types
+
+// RedactedSecretPlaceholder is the fixed value returned in API responses
+// whenever a sensitive field is set but withheld from the client. The empty
+// string ("") is reserved for the orthogonal "not set" state, which lets the
+// frontend distinguish the two states without an extra boolean field.
+//
+// The value matches the placeholder already used by
+// ConnectionConfig.MaskSensitiveFields on VectorStore responses; this package
+// promotes it to a shared constant so every resource agrees on the same
+// sentinel.
+const RedactedSecretPlaceholder = "***"
+
+// IsRedactedOrEmpty reports whether s should be treated as "no change
+// requested" in an Update* request. It returns true for:
+//
+//   - "" — the field was absent from the client payload or explicitly cleared
+//     on the form without using the dedicated Clear* flag
+//   - RedactedSecretPlaceholder — the client echoed back the value it received
+//     in a GET response (for example, a legacy frontend that pre-fills the
+//     edit form with the redacted value)
+//
+// Any other value is an explicit replacement and must be persisted.
+func IsRedactedOrEmpty(s string) bool {
+	return s == "" || s == RedactedSecretPlaceholder
+}
+
+// PreserveIfRedacted returns existing when incoming is empty or the redacted
+// placeholder, otherwise returns incoming. Call this from every Update*
+// service that accepts secret fields in its request DTO to keep the preserve
+// semantics identical across resources.
+func PreserveIfRedacted(incoming, existing string) string {
+	if IsRedactedOrEmpty(incoming) {
+		return existing
+	}
+	return incoming
+}
diff --git a/internal/types/secret_test.go b/internal/types/secret_test.go
new file mode 100644
index 00000000..65162679
--- /dev/null
+++ b/internal/types/secret_test.go
@@ -0,0 +1,51 @@
+package types
+
+import "testing"
+
+func TestIsRedactedOrEmpty(t *testing.T) {
+	tests := []struct {
+		name string
+		in   string
+		want bool
+	}{
+		{"empty string is redacted-or-empty", "", true},
+		{"fixed placeholder is redacted-or-empty", RedactedSecretPlaceholder, true},
+		{"short real secret is not redacted", "ab", false},
+		{"real secret longer than placeholder is not redacted", "real-bearer-token", false},
+		{"secret containing placeholder substring is not redacted", "prefix***suffix", false},
+		{"single asterisk is not redacted", "*", false},
+		{"double asterisk is not redacted", "**", false},
+		{"four asterisks is not redacted (distinct from 3)", "****", false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := IsRedactedOrEmpty(tt.in); got != tt.want {
+				t.Errorf("IsRedactedOrEmpty(%q) = %v, want %v", tt.in, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestPreserveIfRedacted(t *testing.T) {
+	tests := []struct {
+		name     string
+		incoming string
+		existing string
+		want     string
+	}{
+		{"empty incoming preserves existing", "", "stored-secret", "stored-secret"},
+		{"placeholder incoming preserves existing", RedactedSecretPlaceholder, "stored-secret", "stored-secret"},
+		{"real incoming replaces existing", "new-secret", "stored-secret", "new-secret"},
+		{"real incoming replaces empty existing", "new-secret", "", "new-secret"},
+		{"empty incoming with empty existing stays empty", "", "", ""},
+		{"placeholder incoming with empty existing stays empty", RedactedSecretPlaceholder, "", ""},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := PreserveIfRedacted(tt.incoming, tt.existing); got != tt.want {
+				t.Errorf("PreserveIfRedacted(%q, %q) = %q, want %q",
+					tt.incoming, tt.existing, got, tt.want)
+			}
+		})
+	}
+}
diff --git a/internal/types/vectorstore.go b/internal/types/vectorstore.go
index 0425cfe6..82e8a784 100644
--- a/internal/types/vectorstore.go
+++ b/internal/types/vectorstore.go
@@ -194,14 +194,16 @@ func (c ConnectionConfig) GetEndpoint() string {
 	return ""
 }
 
-// MaskSensitiveFields returns a copy with Password and APIKey masked.
+// MaskSensitiveFields returns a copy with Password and APIKey replaced by the
+// shared RedactedSecretPlaceholder. Empty values stay empty so the frontend
+// can distinguish "set (hidden)" from "not set" without an extra flag.
 func (c ConnectionConfig) MaskSensitiveFields() ConnectionConfig {
 	masked := c
 	if masked.Password != "" {
-		masked.Password = "***"
+		masked.Password = RedactedSecretPlaceholder
 	}
 	if masked.APIKey != "" {
-		masked.APIKey = "***"
+		masked.APIKey = RedactedSecretPlaceholder
 	}
 	return masked
 }
diff --git a/internal/types/vectorstore_test.go b/internal/types/vectorstore_test.go
index 296fe646..8d96da9c 100644
--- a/internal/types/vectorstore_test.go
+++ b/internal/types/vectorstore_test.go
@@ -214,8 +214,8 @@ func TestNewVectorStoreResponse(t *testing.T) {
 
 	t.Run("masks sensitive fields", func(t *testing.T) {
 		resp := NewVectorStoreResponse(store, "user", false)
-		assert.Equal(t, "***", resp.ConnectionConfig.Password)
-		assert.Equal(t, "***", resp.ConnectionConfig.APIKey)
+		assert.Equal(t, RedactedSecretPlaceholder, resp.ConnectionConfig.Password)
+		assert.Equal(t, RedactedSecretPlaceholder, resp.ConnectionConfig.APIKey)
 		assert.Equal(t, "http://es:9200", resp.ConnectionConfig.Addr) // non-sensitive preserved
 	})
 
@@ -574,8 +574,8 @@ func TestConnectionConfig_MaskSensitiveFields(t *testing.T) {
 			APIKey:   "sk-api-key",
 		}
 		masked := c.MaskSensitiveFields()
-		assert.Equal(t, "***", masked.Password)
-		assert.Equal(t, "***", masked.APIKey)
+		assert.Equal(t, RedactedSecretPlaceholder, masked.Password)
+		assert.Equal(t, RedactedSecretPlaceholder, masked.APIKey)
 		assert.Equal(t, "http://es:9200", masked.Addr)
 		assert.Equal(t, "elastic", masked.Username)
 	})
diff --git a/internal/types/web_search_provider.go b/internal/types/web_search_provider.go
index 3f0c1245..1b88ade6 100644
--- a/internal/types/web_search_provider.go
+++ b/internal/types/web_search_provider.go
@@ -67,6 +67,12 @@ func (e *WebSearchProviderEntity) BeforeCreate(tx *gorm.DB) (err error) {
 // API keys are encrypted at rest using AES-GCM.
 // BaseURL is intentionally NOT included — each provider type uses a hardcoded
 // official API endpoint to prevent SSRF attacks.
+//
+// ClearAPIKey is a write-only flag used in Update requests to explicitly
+// remove the stored API key. It is never persisted and never returned in
+// responses. Without this flag an empty APIKey in an Update request is
+// interpreted as "no change", so this is the only way to intentionally clear
+// a stored key without deleting the entire provider record.
 type WebSearchProviderParameters struct {
 	// API key for the search provider (encrypted in DB)
 	APIKey string `yaml:"api_key" json:"api_key,omitempty"`
@@ -80,6 +86,42 @@ type WebSearchProviderParameters struct {
 	ProxyURL string `yaml:"proxy_url" json:"proxy_url,omitempty"`
 	// Provider-specific extra configuration for future extensibility
 	ExtraConfig map[string]string `yaml:"extra_config" json:"extra_config,omitempty"`
+
+	// Write-only clear flag — never persisted, never returned.
+	ClearAPIKey bool `yaml:"-" json:"clear_api_key,omitempty" gorm:"-"`
+}
+
+// RedactSensitiveData replaces APIKey with RedactedSecretPlaceholder when a
+// value is set. Empty values stay empty so the frontend can distinguish
+// "set (hidden)" from "not set". Mutates the receiver in place.
+func (e *WebSearchProviderEntity) RedactSensitiveData() {
+	if e.Parameters.APIKey != "" {
+		e.Parameters.APIKey = RedactedSecretPlaceholder
+	}
+	// Write-only flag must never reach the client. omitempty alone is
+	// insufficient because a true value serializes; explicitly clear it so
+	// any response path that runs RedactSensitiveData is safe by construction.
+	e.Parameters.ClearAPIKey = false
+}
+
+// MergeUpdate applies write-only secret merge semantics for Update requests:
+//
+//   - ClearAPIKey takes precedence — when true, APIKey becomes empty
+//   - Otherwise APIKey uses PreserveIfRedacted: empty or the redacted
+//     placeholder preserves existing, any other value replaces
+//   - Non-secret fields (EngineID, ProxyURL, ExtraConfig) are replaced
+//     directly from incoming
+//   - The write-only ClearAPIKey flag is cleared on the merged result so it
+//     never leaks to storage
+func (p WebSearchProviderParameters) MergeUpdate(existing WebSearchProviderParameters) WebSearchProviderParameters {
+	merged := p
+	if p.ClearAPIKey {
+		merged.APIKey = ""
+	} else {
+		merged.APIKey = PreserveIfRedacted(p.APIKey, existing.APIKey)
+	}
+	merged.ClearAPIKey = false
+	return merged
 }
 
 // Value implements the driver.Valuer interface.
diff --git a/internal/types/web_search_provider_test.go b/internal/types/web_search_provider_test.go
new file mode 100644
index 00000000..159402a4
--- /dev/null
+++ b/internal/types/web_search_provider_test.go
@@ -0,0 +1,87 @@
+package types
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestWebSearchProviderEntity_RedactSensitiveData(t *testing.T) {
+	t.Run("redacts set api key", func(t *testing.T) {
+		e := &WebSearchProviderEntity{
+			Parameters: WebSearchProviderParameters{APIKey: "real-key", EngineID: "cse-id"},
+		}
+		e.RedactSensitiveData()
+		assert.Equal(t, RedactedSecretPlaceholder, e.Parameters.APIKey)
+		assert.Equal(t, "cse-id", e.Parameters.EngineID, "non-secret fields preserved")
+	})
+
+	t.Run("leaves empty api key empty", func(t *testing.T) {
+		e := &WebSearchProviderEntity{
+			Parameters: WebSearchProviderParameters{APIKey: "", EngineID: "cse-id"},
+		}
+		e.RedactSensitiveData()
+		assert.Empty(t, e.Parameters.APIKey, "empty must stay empty to signal 'not set' to the frontend")
+	})
+
+	t.Run("zeroes write-only clear flag so it never echoes back", func(t *testing.T) {
+		// Regression for response-side leak: a true ClearAPIKey serializes
+		// despite json:"...,omitempty" because true is not a zero value.
+		e := &WebSearchProviderEntity{
+			Parameters: WebSearchProviderParameters{APIKey: "real-key", ClearAPIKey: true},
+		}
+		e.RedactSensitiveData()
+		assert.False(t, e.Parameters.ClearAPIKey, "ClearAPIKey must be reset before response")
+	})
+}
+
+func TestWebSearchProviderParameters_MergeUpdate(t *testing.T) {
+	existing := WebSearchProviderParameters{
+		APIKey:   "stored-key",
+		EngineID: "stored-engine",
+		ProxyURL: "http://stored-proxy",
+	}
+
+	t.Run("empty api key preserves existing", func(t *testing.T) {
+		in := WebSearchProviderParameters{APIKey: "", EngineID: "new-engine"}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-key", out.APIKey)
+		assert.Equal(t, "new-engine", out.EngineID, "non-secret fields flow from incoming")
+	})
+
+	t.Run("redacted placeholder preserves existing", func(t *testing.T) {
+		in := WebSearchProviderParameters{APIKey: RedactedSecretPlaceholder}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "stored-key", out.APIKey)
+	})
+
+	t.Run("real value replaces existing", func(t *testing.T) {
+		in := WebSearchProviderParameters{APIKey: "new-key"}
+		out := in.MergeUpdate(existing)
+		assert.Equal(t, "new-key", out.APIKey)
+	})
+
+	t.Run("ClearAPIKey wipes stored value", func(t *testing.T) {
+		in := WebSearchProviderParameters{ClearAPIKey: true}
+		out := in.MergeUpdate(existing)
+		assert.Empty(t, out.APIKey)
+	})
+
+	t.Run("ClearAPIKey takes precedence over submitted value", func(t *testing.T) {
+		in := WebSearchProviderParameters{APIKey: "will-be-ignored", ClearAPIKey: true}
+		out := in.MergeUpdate(existing)
+		assert.Empty(t, out.APIKey)
+	})
+
+	t.Run("ClearAPIKey flag never persists on merged result", func(t *testing.T) {
+		in := WebSearchProviderParameters{ClearAPIKey: true}
+		out := in.MergeUpdate(existing)
+		assert.False(t, out.ClearAPIKey, "write-only flag must not leak to storage")
+	})
+
+	t.Run("merge against empty existing", func(t *testing.T) {
+		in := WebSearchProviderParameters{APIKey: RedactedSecretPlaceholder}
+		out := in.MergeUpdate(WebSearchProviderParameters{})
+		assert.Empty(t, out.APIKey, "placeholder against empty preserves empty")
+	})
+}