diff --git a/src/components/ui/Sheet/Sheet.tsx b/src/components/ui/Sheet/Sheet.tsx
index 14a0d3f3..686fe556 100644
--- a/src/components/ui/Sheet/Sheet.tsx
+++ b/src/components/ui/Sheet/Sheet.tsx
@@ -26,6 +26,12 @@ interface SheetProps {
   closeDisabled?: boolean;
   className?: string;
   ariaLabel?: string;
+  /**
+   * If provided, called before starting the close animation when the user
+   * triggers a close (Escape, overlay click, or close button). Return false
+   * (or a Promise that resolves to false) to keep the sheet open.
+   */
+  confirmClose?: () => boolean | Promise<boolean>;
 }
 
 const CLOSE_ANIMATION_DURATION = 280;
@@ -46,6 +52,7 @@ export function Sheet({
   closeDisabled = false,
   className,
   ariaLabel,
+  confirmClose,
   children,
 }: PropsWithChildren<SheetProps>) {
   const { t } = useTranslation();
@@ -106,9 +113,17 @@ export function Sheet({
     };
   }, [open, isVisible, startClose]);
 
-  const handleClose = useCallback(() => {
+  const handleClose = useCallback(async () => {
+    if (confirmClose) {
+      try {
+        const ok = await confirmClose();
+        if (ok === false) return;
+      } catch {
+        return;
+      }
+    }
     startClose(true);
-  }, [startClose]);
+  }, [confirmClose, startClose]);
 
   useEffect(() => {
     return () => {
diff --git a/src/features/providers/sheets/ProviderSheet.tsx b/src/features/providers/sheets/ProviderSheet.tsx
index 74abc030..4813c9d1 100644
--- a/src/features/providers/sheets/ProviderSheet.tsx
+++ b/src/features/providers/sheets/ProviderSheet.tsx
@@ -1,7 +1,8 @@
-import { useCallback, useId, useState } from 'react';
+import { useCallback, useEffect, useId, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Sheet } from '@/components/ui/Sheet';
 import { IconLoader2, IconPencil } from '@/components/ui/icons';
+import { useNotificationStore } from '@/stores';
 import { PROVIDER_DESCRIPTORS } from '../descriptors';
 import type {
   ProviderBrand,
@@ -41,11 +42,48 @@ export function ProviderSheet({
   onUpdated,
 }: ProviderSheetProps) {
   const { t } = useTranslation();
+  const { showConfirmation } = useNotificationStore();
   const formId = useId();
   const [submitting, setSubmitting] = useState(false);
+  const [isDirty, setIsDirty] = useState(false);
+
+  // Reset dirty flag whenever the sheet is closed or the editing target
+  // (brand / resource / mode) changes — the child form will re-mount and
+  // re-report its own dirty state.
+  useEffect(() => {
+    setIsDirty(false);
+  }, [state.brand, state.mode, state.resource?.id, state.open]);
+
+  const handleDirtyChange = useCallback((dirty: boolean) => {
+    setIsDirty(dirty);
+  }, []);
 
   const descriptor = PROVIDER_DESCRIPTORS[state.brand];
   const isAmpcode = state.brand === 'ampcode';
+  const isEditingForm = state.mode === 'create' || state.mode === 'edit';
+
+  const confirmDiscardIfDirty = useCallback((): Promise<boolean> => {
+    if (!isEditingForm || !isDirty || submitting) {
+      return Promise.resolve(true);
+    }
+    return new Promise<boolean>((resolve) => {
+      showConfirmation({
+        title: t('providersPage.unsavedChanges.title'),
+        message: t('providersPage.unsavedChanges.message'),
+        variant: 'danger',
+        confirmText: t('providersPage.unsavedChanges.discard'),
+        cancelText: t('providersPage.unsavedChanges.keepEditing'),
+        onConfirm: () => resolve(true),
+        onCancel: () => resolve(false),
+      });
+    });
+  }, [isDirty, isEditingForm, showConfirmation, submitting, t]);
+
+  const handleCancelClick = useCallback(() => {
+    void confirmDiscardIfDirty().then((ok) => {
+      if (ok) onClose();
+    });
+  }, [confirmDiscardIfDirty, onClose]);
 
   const titleText =
     state.mode === 'create'
@@ -116,6 +154,7 @@ export function ProviderSheet({
           mutating={submitting || workbench.mutating}
           formId={formId}
           onSubmit={handleAmpcodeSubmit}
+          onDirtyChange={handleDirtyChange}
         />
       );
     }
@@ -128,6 +167,7 @@ export function ProviderSheet({
         mutating={submitting || workbench.mutating}
         formId={formId}
         onSubmit={state.mode === 'create' ? handleCreate : handleUpdate}
+        onDirtyChange={handleDirtyChange}
       />
     );
   };
@@ -166,7 +206,7 @@ export function ProviderSheet({
         <button
           type="button"
           className={`${styles.footerBtn} ${styles.footerBtnGhost}`}
-          onClick={onClose}
+          onClick={handleCancelClick}
           disabled={submitting}
         >
           {t('providersPage.actions.cancel')}
@@ -205,6 +245,7 @@ export function ProviderSheet({
       })}
       footer={footer}
       closeDisabled={submitting}
+      confirmClose={confirmDiscardIfDirty}
     >
       {renderBody()}
     </Sheet>
diff --git a/src/features/providers/sheets/forms/AmpcodeForm.tsx b/src/features/providers/sheets/forms/AmpcodeForm.tsx
index 1891bef8..7e62f543 100644
--- a/src/features/providers/sheets/forms/AmpcodeForm.tsx
+++ b/src/features/providers/sheets/forms/AmpcodeForm.tsx
@@ -1,4 +1,4 @@
-import { useId, useState } from 'react';
+import { useEffect, useId, useMemo, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Collapsible } from '@/components/ui/Collapsible';
 import { IconPlus, IconX } from '@/components/ui/icons';
@@ -52,6 +52,7 @@ interface AmpcodeFormProps {
   mutating: boolean;
   formId: string;
   onSubmit: (config: AmpcodeConfig) => Promise<void>;
+  onDirtyChange?: (dirty: boolean) => void;
 }
 
 export function AmpcodeForm({
@@ -59,13 +60,26 @@ export function AmpcodeForm({
   mutating,
   formId,
   onSubmit,
+  onDirtyChange,
 }: AmpcodeFormProps) {
   const { t } = useTranslation();
   const fid = useId();
   const initialConfig = (resource?.raw as AmpcodeConfig | undefined) ?? {};
   const [form, setForm] = useState<AmpcodeFormState>(() => buildState(initialConfig));
+  const [initialFormSignature] = useState<string>(() =>
+    JSON.stringify(buildState(initialConfig))
+  );
   const [error, setError] = useState<string | null>(null);
 
+  const isDirty = useMemo(
+    () => JSON.stringify(form) !== initialFormSignature,
+    [form, initialFormSignature]
+  );
+
+  useEffect(() => {
+    onDirtyChange?.(isDirty);
+  }, [isDirty, onDirtyChange]);
+
   const handleSubmit = async (e: React.FormEvent<HTMLFormElement>) => {
     e.preventDefault();
     try {
diff --git a/src/features/providers/sheets/forms/BaseProviderForm.tsx b/src/features/providers/sheets/forms/BaseProviderForm.tsx
index 508f7903..eed645a3 100644
--- a/src/features/providers/sheets/forms/BaseProviderForm.tsx
+++ b/src/features/providers/sheets/forms/BaseProviderForm.tsx
@@ -1,4 +1,4 @@
-import { useId, useMemo, useState } from 'react';
+import { useEffect, useId, useMemo, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import {
   IconAlertTriangle,
@@ -44,6 +44,7 @@ interface BaseProviderFormProps {
   mutating: boolean;
   formId: string;
   onSubmit: (input: ProviderEntryFormInput) => Promise<void>;
+  onDirtyChange?: (dirty: boolean) => void;
 }
 
 const emptyHeader = () => ({ key: '', value: '' });
@@ -196,6 +197,7 @@ export function BaseProviderForm({
   mutating,
   formId,
   onSubmit,
+  onDirtyChange,
 }: BaseProviderFormProps) {
   const { t } = useTranslation();
   const descriptor = PROVIDER_DESCRIPTORS[brand];
@@ -203,8 +205,20 @@ export function BaseProviderForm({
   const [form, setForm] = useState<ProviderEntryFormInput>(() =>
     buildInitialForm(brand, resource, mode)
   );
+  const [initialFormSignature] = useState<string>(() =>
+    JSON.stringify(buildInitialForm(brand, resource, mode))
+  );
   const [error, setError] = useState<string | null>(null);
 
+  const isDirty = useMemo(
+    () => JSON.stringify(form) !== initialFormSignature,
+    [form, initialFormSignature]
+  );
+
+  useEffect(() => {
+    onDirtyChange?.(isDirty);
+  }, [isDirty, onDirtyChange]);
+
   const fallbackApiKey = useMemo(() => {
     if (mode !== 'edit' || !resource) return '';
     if (brand === 'openaiCompatibility') return '';
diff --git a/src/i18n/locales/en.json b/src/i18n/locales/en.json
index 1111aec4..e8cad369 100644
--- a/src/i18n/locales/en.json
+++ b/src/i18n/locales/en.json
@@ -1600,6 +1600,12 @@
       "disabled": "Disabled",
       "toggleFailed": "Failed to update status"
     },
+    "unsavedChanges": {
+      "title": "Discard unsaved changes?",
+      "message": "You have unsaved edits in this form. Closing will discard them.",
+      "discard": "Discard changes",
+      "keepEditing": "Keep editing"
+    },
     "connectivity": {
       "test": "Test",
       "testAll": "Test all",
diff --git a/src/i18n/locales/ru.json b/src/i18n/locales/ru.json
index c0ae0639..7139fd80 100644
--- a/src/i18n/locales/ru.json
+++ b/src/i18n/locales/ru.json
@@ -1597,6 +1597,12 @@
       "disabled": "Отключено",
       "toggleFailed": "Не удалось обновить статус"
     },
+    "unsavedChanges": {
+      "title": "Отменить несохранённые изменения?",
+      "message": "В форме есть несохранённые изменения. При закрытии они будут потеряны.",
+      "discard": "Отменить изменения",
+      "keepEditing": "Продолжить"
+    },
     "connectivity": {
       "test": "Проверить",
       "testAll": "Проверить все",
diff --git a/src/i18n/locales/zh-CN.json b/src/i18n/locales/zh-CN.json
index 5d322726..f25ca732 100644
--- a/src/i18n/locales/zh-CN.json
+++ b/src/i18n/locales/zh-CN.json
@@ -1600,6 +1600,12 @@
       "disabled": "已停用",
       "toggleFailed": "更新状态失败"
     },
+    "unsavedChanges": {
+      "title": "确定丢弃未保存的修改吗?",
+      "message": "当前表单还有未保存的修改,关闭后会被丢弃。",
+      "discard": "丢弃修改",
+      "keepEditing": "继续编辑"
+    },
     "connectivity": {
       "test": "测试",
       "testAll": "全部测试",
diff --git a/src/i18n/locales/zh-TW.json b/src/i18n/locales/zh-TW.json
index 9baf67e6..80cccb54 100644
--- a/src/i18n/locales/zh-TW.json
+++ b/src/i18n/locales/zh-TW.json
@@ -1626,6 +1626,12 @@
       "disabled": "已停用",
       "toggleFailed": "更新狀態失敗"
     },
+    "unsavedChanges": {
+      "title": "確定捨棄未儲存的變更嗎?",
+      "message": "目前表單還有尚未儲存的變更,關閉後會遺失。",
+      "discard": "捨棄變更",
+      "keepEditing": "繼續編輯"
+    },
     "connectivity": {
       "test": "測試",
       "testAll": "全部測試",