diff --git a/frontend-web/src/components/workspace/settings/skill-settings-page.tsx b/frontend-web/src/components/workspace/settings/skill-settings-page.tsx
index 4f6a3e7d..42f92a24 100644
--- a/frontend-web/src/components/workspace/settings/skill-settings-page.tsx
+++ b/frontend-web/src/components/workspace/settings/skill-settings-page.tsx
@@ -71,8 +71,9 @@ import { useTheme } from "@/contexts/ThemeContext";
 import { getStoredAuth } from "@/core/auth";
 import { useI18n } from "@/core/i18n/hooks";
 import type { ValidateSkillUploadResponse } from "@/core/skills/api";
-import {
-  useDeleteCustomSkill,
+import {
+  useDeleteBuiltinSkill,
+  useDeleteCustomSkill,
   useDuplicateSkill,
   useGenerateMissingSkillNameZh,
   useGenerateSkillNameZh,
@@ -616,9 +617,10 @@ export function SkillRow({
   const { data: cardPublishSquares } = usePublishSquares();
   const setPinned = useSetSkillPinned();
   const setFeatured = useSetSkillFeatured();
-  const setAlwaysOn = useSetSkillAlwaysOn();
-  const { data: compression } = useSkillCompressionSettings();
-  const deleteSkill = useDeleteCustomSkill();
+  const setAlwaysOn = useSetSkillAlwaysOn();
+  const { data: compression } = useSkillCompressionSettings();
+  const deleteCustom = useDeleteCustomSkill();
+  const deleteBuiltin = useDeleteBuiltinSkill();
   const duplicateSkillMutation = useDuplicateSkill();
   const [confirmDeleteOpen, setConfirmDeleteOpen] = useState(false);
   const [tagPickerOpen, setTagPickerOpen] = useState(false);
@@ -634,8 +636,9 @@ export function SkillRow({
   const isOwned =
     isCustom && !isBuiltin && !!skill.owner_user_id && skill.owner_user_id === currentUserId;
   const isFromOthers = isCustom && !isBuiltin && !isOwned;
-  // Admin can edit/delete/unpublish anyone's skill; non-admin only their own.
-  const canManage = isCustom && (isOwned || isAdmin);
+  // Admin can manage custom skills from any owner; non-admin only their own.
+  const canManage = isCustom && (isOwned || isAdmin);
+  const canDelete = isAdmin || isOwned;
   const canTogglePublish = canManage && !isBuiltin;
   // 常驻(免压缩):内置技能仅管理员可设;自定义技能其所有者或管理员可设(与后端一致)。
   const canSetAlwaysOn = isAdmin || isOwned;
@@ -686,11 +689,15 @@ export function SkillRow({
     }
   }
 
-  async function handleDelete() {
-    try {
-      await deleteSkill.mutateAsync(skill.name);
-      toast.success(t.settings.skills.deleteSuccess);
-      setConfirmDeleteOpen(false);
+  async function handleDelete() {
+    try {
+      if (isBuiltin) {
+        await deleteBuiltin.mutateAsync(skill.name);
+      } else {
+        await deleteCustom.mutateAsync(skill.name);
+      }
+      toast.success(t.settings.skills.deleteSuccess);
+      setConfirmDeleteOpen(false);
     } catch (err) {
       toast.error(err instanceof Error ? err.message : String(err));
     }
@@ -918,7 +925,7 @@ export function SkillRow({
       >
         <TagsIcon className="size-3.5" />
       </Button>
-      {canManage && (
+      {canManage && (
         <Button
           size="icon"
           variant="ghost"
@@ -939,12 +946,12 @@ export function SkillRow({
           />
         </Button>
       )}
-      {canManage && (
-        <Button
-          size="icon"
-          variant="ghost"
-          className={cn(
-            "h-8 w-8 shrink-0",
+      {canManage && (
+        <Button
+          size="icon"
+          variant="ghost"
+          className={cn(
+            "h-8 w-8 shrink-0",
             skill.pinned && "text-emerald-600 hover:text-emerald-700",
           )}
           disabled={setPinned.isPending}
@@ -1011,11 +1018,11 @@ export function SkillRow({
       >
         <CopyIcon className="size-3.5" />
       </Button>
-      {canManage && (
-        <Button
-          size="icon"
-          variant="ghost"
-          className="text-destructive hover:text-destructive h-8 w-8 shrink-0"
+      {canDelete && (
+        <Button
+          size="icon"
+          variant="ghost"
+          className="text-destructive hover:text-destructive h-8 w-8 shrink-0"
           onClick={() => setConfirmDeleteOpen(true)}
           title={t.settings.skills.deleteAction}
         >
@@ -1109,16 +1116,18 @@ export function SkillRow({
             <Button
               variant="outline"
               onClick={() => setConfirmDeleteOpen(false)}
-              disabled={deleteSkill.isPending}
+              disabled={deleteCustom.isPending || deleteBuiltin.isPending}
             >
               {t.common.cancel}
             </Button>
             <Button
               variant="destructive"
               onClick={() => void handleDelete()}
-              disabled={deleteSkill.isPending}
-            >
-              {deleteSkill.isPending ? t.common.loading : t.common.delete}
+              disabled={deleteCustom.isPending || deleteBuiltin.isPending}
+            >
+              {deleteCustom.isPending || deleteBuiltin.isPending
+                ? t.common.loading
+                : t.common.delete}
             </Button>
           </DialogFooter>
         </DialogContent>
diff --git a/frontend-web/src/components/workspace/skills/skill-file-preview-dialog.tsx b/frontend-web/src/components/workspace/skills/skill-file-preview-dialog.tsx
index 000aa9ae..d9a75f45 100644
--- a/frontend-web/src/components/workspace/skills/skill-file-preview-dialog.tsx
+++ b/frontend-web/src/components/workspace/skills/skill-file-preview-dialog.tsx
@@ -5,6 +5,7 @@ import {
   DownloadIcon,
   Loader2,
   PencilIcon,
+  Trash2Icon,
   XIcon,
 } from "lucide-react";
 import { useEffect, useMemo, useState } from "react";
@@ -22,6 +23,7 @@ import { Textarea } from "@/components/ui/textarea";
 import { MarkdownContent } from "@/components/workspace/messages/markdown-content";
 import { getSkillFileDownloadURL } from "@/core/skills/api";
 import {
+  useDeleteSkillFile,
   useSaveSkillFile,
   useSkillFileContent,
 } from "@/core/skills/hooks";
@@ -66,6 +68,7 @@ export function SkillFilePreviewDialog({
     open ? path : null,
   );
   const save = useSaveSkillFile();
+  const remove = useDeleteSkillFile();
 
   const [editing, setEditing] = useState(false);
   const [draft, setDraft] = useState("");
@@ -77,6 +80,8 @@ export function SkillFilePreviewDialog({
   }, [path, open]);
 
   const fileEditable = !!data?.editable && treeEditable;
+  const isRootSkillFile = path?.replace(/\\/g, "/").toLowerCase() === "skill.md";
+  const fileDeletable = !!data && treeEditable && !isRootSkillFile;
   const isMarkdown = useMemo(() => {
     if (!path) return false;
     const lower = path.toLowerCase();
@@ -115,6 +120,18 @@ export function SkillFilePreviewDialog({
     }
   }
 
+  async function handleDelete() {
+    if (!skillName || !path) return;
+    if (!window.confirm(tx.filesDeleteConfirm.replace("{path}", path))) return;
+    try {
+      await remove.mutateAsync({ skillName, path });
+      toast.success(tx.filesDeleteSuccess);
+      onOpenChange(false);
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : String(err));
+    }
+  }
+
   async function handleCopyPath() {
     if (!path) return;
     await navigator.clipboard.writeText(path);
@@ -158,6 +175,18 @@ export function SkillFilePreviewDialog({
                   {tx.filesEditAction}
                 </Button>
               )}
+              {fileDeletable && !editing && (
+                <Button
+                  size="sm"
+                  variant="ghost"
+                  className="h-7 px-2 text-xs text-destructive hover:text-destructive"
+                  onClick={() => void handleDelete()}
+                  disabled={remove.isPending}
+                >
+                  {remove.isPending ? <Loader2 className="size-3.5 animate-spin" /> : <Trash2Icon className="size-3.5" />}
+                  {tx.filesDeleteAction}
+                </Button>
+              )}
               {editing && (
                 <>
                   <Button
diff --git a/frontend-web/src/core/i18n/locales/en-US.ts b/frontend-web/src/core/i18n/locales/en-US.ts
index ebaae531..de6a7d60 100644
--- a/frontend-web/src/core/i18n/locales/en-US.ts
+++ b/frontend-web/src/core/i18n/locales/en-US.ts
@@ -545,10 +545,13 @@ export const enUS: Translations = {
       filesSaveAction: "Save",
       filesCancelEditAction: "Cancel",
       filesDownloadAction: "Download",
-      filesCopyPathAction: "Copy path",
-      filesDiscardConfirm: "Discard unsaved changes?",
-      filesSaveSuccess: "File saved",
-      filesReadOnlyHint: "Built-in skills are read-only.",
+      filesCopyPathAction: "Copy path",
+      filesDiscardConfirm: "Discard unsaved changes?",
+      filesSaveSuccess: "File saved",
+      filesDeleteAction: "Delete",
+      filesDeleteConfirm: "Delete \"{path}\"? This cannot be undone.",
+      filesDeleteSuccess: "File deleted",
+      filesReadOnlyHint: "Only administrators can edit or delete built-in skill files.",
       viewDetailAction: "View skill details",
       stateSheet: {
         archivedTitle: "Archived skills",
diff --git a/frontend-web/src/core/i18n/locales/types.ts b/frontend-web/src/core/i18n/locales/types.ts
index 2dc0c0c6..3cbdf9c0 100644
--- a/frontend-web/src/core/i18n/locales/types.ts
+++ b/frontend-web/src/core/i18n/locales/types.ts
@@ -475,10 +475,13 @@ export interface Translations {
       filesSaveAction: string;
       filesCancelEditAction: string;
       filesDownloadAction: string;
-      filesCopyPathAction: string;
-      filesDiscardConfirm: string;
-      filesSaveSuccess: string;
-      filesReadOnlyHint: string;
+      filesCopyPathAction: string;
+      filesDiscardConfirm: string;
+      filesSaveSuccess: string;
+      filesDeleteAction: string;
+      filesDeleteConfirm: string;
+      filesDeleteSuccess: string;
+      filesReadOnlyHint: string;
       viewDetailAction: string;
       stateSheet: {
         archivedTitle: string;
diff --git a/frontend-web/src/core/i18n/locales/zh-CN.ts b/frontend-web/src/core/i18n/locales/zh-CN.ts
index 98ecbb27..ab06ad4a 100644
--- a/frontend-web/src/core/i18n/locales/zh-CN.ts
+++ b/frontend-web/src/core/i18n/locales/zh-CN.ts
@@ -524,8 +524,11 @@ export const zhCN: Translations = {
       filesDownloadAction: "下载",
       filesCopyPathAction: "复制路径",
       filesDiscardConfirm: "有未保存的修改,确定放弃吗?",
-      filesSaveSuccess: "文件已保存",
-      filesReadOnlyHint: "内置技能为只读,仅可查看。",
+      filesSaveSuccess: "文件已保存",
+      filesDeleteAction: "删除",
+      filesDeleteConfirm: "确定删除“{path}”？该操作不可撤销。",
+      filesDeleteSuccess: "文件已删除",
+      filesReadOnlyHint: "仅管理员可以编辑或删除内置技能文件。",
       viewDetailAction: "查看技能详情",
       stateSheet: {
         archivedTitle: "归档的技能",
diff --git a/frontend-web/src/core/skills/api.ts b/frontend-web/src/core/skills/api.ts
index 0117455e..947a7395 100644
--- a/frontend-web/src/core/skills/api.ts
+++ b/frontend-web/src/core/skills/api.ts
@@ -402,15 +402,26 @@ export async function getSkillContent(
   return response.json() as Promise<SkillContentResponse>;
 }
 
-export async function deleteCustomSkill(skillName: string): Promise<void> {
+export async function deleteCustomSkill(skillName: string): Promise<void> {
   const response = await apiFetch(
     `${getBackendBaseURL()}/api/skills/custom/${encodeURIComponent(skillName)}`,
     { method: "DELETE" },
   );
   if (!response.ok) {
     throw await parseDetailedError(response, "Failed to delete skill");
-  }
-}
+  }
+}
+
+/** Delete a built-in skill. The backend permits this only for administrators. */
+export async function deleteBuiltinSkill(skillName: string): Promise<void> {
+  const response = await apiFetch(
+    `${getBackendBaseURL()}/api/skills/${encodeURIComponent(skillName)}`,
+    { method: "DELETE" },
+  );
+  if (!response.ok) {
+    throw await parseDetailedError(response, "Failed to delete built-in skill");
+  }
+}
 
 export interface SkillFileNode {
   name: string;
@@ -479,7 +490,7 @@ export function getSkillFileDownloadURL(skillName: string, path: string): string
   );
 }
 
-export async function saveSkillFile(
+export async function saveSkillFile(
   skillName: string,
   path: string,
   content: string,
@@ -494,9 +505,22 @@ export async function saveSkillFile(
   );
   if (!response.ok) {
     throw await parseDetailedError(response, "Failed to save skill file");
-  }
-  return response.json() as Promise<SkillFileSaveResponse>;
-}
+  }
+  return response.json() as Promise<SkillFileSaveResponse>;
+}
+
+export async function deleteSkillFile(
+  skillName: string,
+  path: string,
+): Promise<void> {
+  const url =
+    `${getBackendBaseURL()}/api/skills/${encodeURIComponent(skillName)}/files/content` +
+    `?path=${encodeURIComponent(path)}`;
+  const response = await apiFetch(url, { method: "DELETE" });
+  if (!response.ok) {
+    throw await parseDetailedError(response, "Failed to delete skill file");
+  }
+}
 
 export interface SkillNameZhResponse {
   name: string;
diff --git a/frontend-web/src/core/skills/hooks.ts b/frontend-web/src/core/skills/hooks.ts
index 4460242e..ad68d7d5 100644
--- a/frontend-web/src/core/skills/hooks.ts
+++ b/frontend-web/src/core/skills/hooks.ts
@@ -5,8 +5,10 @@ import {
   useQueryClient,
 } from "@tanstack/react-query";
 
-import {
-  deleteCustomSkill,
+import {
+  deleteBuiltinSkill,
+  deleteCustomSkill,
+  deleteSkillFile,
   duplicateSkill,
   enableSkill,
   generateMissingSkillNameZh,
@@ -318,7 +320,7 @@ export function useSkillFileContent(skillName: string | null, path: string | nul
   });
 }
 
-export function useSaveSkillFile() {
+export function useSaveSkillFile() {
   const queryClient = useQueryClient();
   return useMutation({
     mutationFn: ({
@@ -339,5 +341,33 @@ export function useSaveSkillFile() {
         void queryClient.invalidateQueries({ queryKey: ["skill", skillName] });
       }
     },
-  });
-}
+  });
+}
+
+export function useDeleteSkillFile() {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: ({
+      skillName,
+      path,
+    }: {
+      skillName: string;
+      path: string;
+    }) => deleteSkillFile(skillName, path),
+    onSuccess: (_data, { skillName, path }) => {
+      void queryClient.invalidateQueries({ queryKey: ["skill-files", skillName] });
+      void queryClient.removeQueries({ queryKey: ["skill-file", skillName, path] });
+    },
+  });
+}
+
+export function useDeleteBuiltinSkill() {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: deleteBuiltinSkill,
+    onSuccess: () => {
+      void queryClient.invalidateQueries({ queryKey: ["skills"] });
+      void queryClient.invalidateQueries({ queryKey: ["admin-skills"] });
+    },
+  });
+}
diff --git a/offline-backend-20260512/backend/app/gateway/routers/skills.py b/offline-backend-20260512/backend/app/gateway/routers/skills.py
index 47b14483..07d3f418 100644
--- a/offline-backend-20260512/backend/app/gateway/routers/skills.py
+++ b/offline-backend-20260512/backend/app/gateway/routers/skills.py
@@ -1622,6 +1622,102 @@ async def delete_custom_skill(
         raise HTTPException(status_code=500, detail=f"Failed to delete custom skill: {str(e)}")
 
 
+def _remove_skill_state_config(skill_name: str) -> None:
+    """Remove a deleted skill's enabled/display override from extensions config."""
+    extensions_config = get_extensions_config()
+    if skill_name not in extensions_config.skills:
+        return
+
+    config_path = ExtensionsConfig.resolve_config_path()
+    if config_path is None:
+        config_path = Path.cwd().parent / "extensions_config.json"
+    extensions_config.skills.pop(skill_name, None)
+    config_data = _dump_extensions_config(extensions_config)
+
+    tmp_path: Path | None = None
+    try:
+        with tempfile.NamedTemporaryFile(
+            "w",
+            encoding="utf-8",
+            delete=False,
+            dir=str(config_path.parent),
+        ) as tmp_file:
+            json.dump(config_data, tmp_file, indent=2)
+            tmp_path = Path(tmp_file.name)
+        os.replace(tmp_path, config_path)
+    finally:
+        if tmp_path is not None and tmp_path.exists():
+            tmp_path.unlink()
+    reload_extensions_config()
+
+
+@router.delete(
+    "/skills/{skill_name}",
+    summary="Delete Built-in Skill",
+    description=(
+        "Administrators may permanently delete a built-in skill. The skill is "
+        "removed from enabled configuration and detached from agents that used it."
+    ),
+)
+async def delete_builtin_skill(
+    skill_name: str,
+    request: Request,
+    config: AppConfig = Depends(get_config),
+    skill_store: SkillStore = Depends(get_skill_store),
+    agent_store=Depends(get_agent_store),
+) -> dict[str, bool]:
+    try:
+        if not _is_admin_user(request):
+            raise HTTPException(status_code=403, detail="Only administrators can delete built-in skills")
+
+        skill_name = _normalize_skill_name_param(skill_name)
+        skill = _load_skill_or_404(skill_name, config)
+        if skill.category != SkillCategory.PUBLIC:
+            raise HTTPException(status_code=400, detail="Use the custom skill deletion endpoint for a custom skill")
+
+        storage = get_or_new_skill_storage(app_config=config)
+        public_root = (storage.get_skills_root_path() / SkillCategory.PUBLIC.value).resolve()
+        skill_dir = skill.skill_file.parent.resolve()
+        if skill_dir == public_root or public_root not in skill_dir.parents:
+            raise ValueError(f"Refusing to delete built-in skill outside the public skills directory: {skill.name}")
+
+        _remove_skill_state_config(skill.name)
+        shutil.rmtree(skill_dir)
+
+        try:
+            from deerflow.skills.usage import forget
+
+            forget(skill.name)
+        except Exception:
+            pass
+
+        await skill_store.delete_admin(skill.name)
+        try:
+            await get_tag_store(request).unassign_all("skill", skill.name)
+        except Exception:  # noqa: BLE001 -- tag cleanup must not block deletion
+            pass
+
+        await cascade_skill_unpublished_or_deleted(
+            skill.name,
+            actor_user_id=_current_user_id(request),
+            operation="delete",
+            skill_owner_user_id=None,
+            agent_store=agent_store,
+        )
+        await refresh_skills_system_prompt_cache_async()
+        logger.info("Administrator deleted built-in skill %s", skill.name)
+        return {"success": True}
+    except HTTPException:
+        raise
+    except FileNotFoundError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+    except Exception as e:
+        logger.error("Failed to delete built-in skill %s: %s", skill_name, e, exc_info=True)
+        raise HTTPException(status_code=500, detail=f"Failed to delete built-in skill: {str(e)}")
+
+
 class SkillPublishRequest(BaseModel):
     """Request body for toggling a custom skill's published flag."""
 
@@ -2080,11 +2176,16 @@ def _caller_can_edit_skill_files(
     record: dict[str, Any] | None,
     request: Request,
 ) -> bool:
-    """Editing is limited to custom skills, and to either owner or admin."""
-    if skill.category != SkillCategory.CUSTOM:
-        return False
+    """Whether the caller can edit or delete a file within *skill*.
+
+    Built-in skills are deployment-owned, so only administrators may change
+    their files. Custom skills remain editable by their owner or by an
+    administrator.
+    """
     if _is_admin_user(request):
         return True
+    if skill.category != SkillCategory.CUSTOM:
+        return False
     if record is None:
         return False
     return record.get("owner_user_id") == _current_user_id(request)
@@ -2125,6 +2226,24 @@ def _is_text_file(path: Path) -> bool:
     return path.suffix.lower() in _SKILL_FILE_TEXT_EXTS
 
 
+def _write_skill_text_file_atomically(target: Path, content: str) -> None:
+    """Replace an already-validated skill file without exposing partial text."""
+    tmp_path: Path | None = None
+    try:
+        with tempfile.NamedTemporaryFile(
+            "w",
+            encoding="utf-8",
+            delete=False,
+            dir=str(target.parent),
+        ) as tmp_file:
+            tmp_file.write(content)
+            tmp_path = Path(tmp_file.name)
+        os.replace(tmp_path, target)
+    finally:
+        if tmp_path is not None and tmp_path.exists():
+            tmp_path.unlink()
+
+
 def _build_skill_file_tree(skill_dir: Path) -> SkillFileNode:
     """Walk *skill_dir* and build a SkillFileNode tree, depth/count capped.
 
@@ -2302,9 +2421,9 @@ async def download_skill_file(
     response_model=SkillFileSaveResponse,
     summary="Write Skill File (Text)",
     description=(
-        "Replace the contents of a text file under a custom skill. Only the "
-        "skill's owner or an admin may write; built-in (public) skills are "
-        "read-only. Edits to ``SKILL.md`` re-validate its YAML frontmatter and "
+        "Replace the contents of a text file under a skill. Administrators may "
+        "write built-in and custom skills; custom-skill owners may write their "
+        "own skills. Edits to ``SKILL.md`` re-validate its YAML frontmatter and "
         "refresh the system-prompt cache."
     ),
 )
@@ -2318,11 +2437,9 @@ async def save_skill_file(
     try:
         skill_name = _normalize_skill_name_param(skill_name)
         skill = _load_skill_or_404(skill_name, config)
-        if skill.category != SkillCategory.CUSTOM:
-            raise HTTPException(status_code=403, detail="Built-in skills are read-only")
         record = await skill_store.get_any(skill.name)
         if not _caller_can_edit_skill_files(skill, record, request):
-            raise HTTPException(status_code=403, detail="Only the skill owner or an admin can edit files in this skill")
+            raise HTTPException(status_code=403, detail="Only an administrator or the custom skill owner can edit files in this skill")
 
         target = _resolve_skill_relative_path(skill, body.path)
         if not target.exists():
@@ -2338,7 +2455,7 @@ async def save_skill_file(
         relative_posix = target.relative_to(skill.skill_file.parent.resolve()).as_posix()
         storage = get_or_new_skill_storage(app_config=config)
 
-        is_skill_md = relative_posix == SKILL_MD_FILE
+        is_skill_md = relative_posix.casefold() == SKILL_MD_FILE.casefold()
         prev_content: str | None = None
         if target.exists():
             try:
@@ -2350,20 +2467,21 @@ async def save_skill_file(
             # SKILL.md edits must keep their frontmatter valid (name must match).
             storage.validate_skill_markdown_content(skill.name, body.content)
 
-        storage.write_custom_skill(skill.name, relative_posix, body.content)
+        _write_skill_text_file_atomically(target, body.content)
 
         try:
-            storage.append_history(
-                skill.name,
-                {
-                    "action": "human_edit_file",
-                    "author": "human",
-                    "thread_id": None,
-                    "file_path": relative_posix,
-                    "prev_content": prev_content,
-                    "new_content": body.content,
-                },
-            )
+            if skill.category == SkillCategory.CUSTOM:
+                storage.append_history(
+                    skill.name,
+                    {
+                        "action": "human_edit_file",
+                        "author": "human",
+                        "thread_id": None,
+                        "file_path": relative_posix,
+                        "prev_content": prev_content,
+                        "new_content": body.content,
+                    },
+                )
         except Exception as history_err:  # noqa: BLE001 — history is best-effort
             logger.warning("Failed to append edit history for %s/%s: %s", skill.name, relative_posix, history_err)
 
@@ -2393,6 +2511,75 @@ async def save_skill_file(
         raise HTTPException(status_code=500, detail=f"Failed to save skill file: {e}")
 
 
+@router.delete(
+    "/skills/{skill_name}/files/content",
+    status_code=204,
+    summary="Delete Skill File",
+    description=(
+        "Delete one non-SKILL.md file under a skill. Administrators may delete "
+        "files from built-in and custom skills; custom-skill owners may delete "
+        "files from their own skills. The root ``SKILL.md`` manifest cannot be "
+        "deleted because it defines the skill."
+    ),
+)
+async def delete_skill_file(
+    skill_name: str,
+    request: Request,
+    path: str = Query(..., description="File path relative to the skill directory"),
+    config: AppConfig = Depends(get_config),
+    skill_store: SkillStore = Depends(get_skill_store),
+) -> None:
+    try:
+        skill_name = _normalize_skill_name_param(skill_name)
+        skill = _load_skill_or_404(skill_name, config)
+        record = await skill_store.get_any(skill.name)
+        if not _caller_can_edit_skill_files(skill, record, request):
+            raise HTTPException(status_code=403, detail="Only an administrator or the custom skill owner can delete files in this skill")
+
+        target = _resolve_skill_relative_path(skill, path)
+        if not target.exists() or not target.is_file():
+            raise HTTPException(status_code=404, detail=f"File '{path}' not found in skill '{skill_name}'")
+
+        relative_posix = target.relative_to(skill.skill_file.parent.resolve()).as_posix()
+        if relative_posix.casefold() == SKILL_MD_FILE.casefold():
+            raise HTTPException(status_code=400, detail="SKILL.md defines the skill and cannot be deleted")
+
+        prev_content: str | None = None
+        if _is_text_file(target):
+            try:
+                prev_content = target.read_text(encoding="utf-8")
+            except UnicodeDecodeError:
+                pass
+        target.unlink()
+
+        if skill.category == SkillCategory.CUSTOM:
+            storage = get_or_new_skill_storage(app_config=config)
+            try:
+                storage.append_history(
+                    skill.name,
+                    {
+                        "action": "human_delete_file",
+                        "author": "human",
+                        "thread_id": None,
+                        "file_path": relative_posix,
+                        "prev_content": prev_content,
+                    },
+                )
+            except Exception as history_err:  # noqa: BLE001
+                logger.warning("Failed to append deletion history for %s/%s: %s", skill.name, relative_posix, history_err)
+        else:
+            logger.info("Administrator deleted built-in skill file %s/%s", skill.name, relative_posix)
+    except HTTPException:
+        raise
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+    except FileNotFoundError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+    except Exception as e:
+        logger.error("Failed to delete skill file %s/%s: %s", skill_name, path, e, exc_info=True)
+        raise HTTPException(status_code=500, detail=f"Failed to delete skill file: {e}")
+
+
 @router.put(
     "/skills/{skill_name}",
     response_model=SkillResponse,
diff --git a/offline-backend-20260512/backend/packages/harness/deerflow/skills/types.py b/offline-backend-20260512/backend/packages/harness/deerflow/skills/types.py
index 0e5b9baf..fb964198 100644
--- a/offline-backend-20260512/backend/packages/harness/deerflow/skills/types.py
+++ b/offline-backend-20260512/backend/packages/harness/deerflow/skills/types.py
@@ -8,7 +8,7 @@ SKILL_MD_FILE = "SKILL.md"
 class SkillCategory(StrEnum):
     """Source category for a skill.
 
-    - ``PUBLIC``: built-in skill bundled with the platform, read-only.
+    - ``PUBLIC``: built-in skill bundled with the platform; administrator-managed.
     - ``CUSTOM``: user-authored skill that can be edited or deleted.
     """