diff --git a/src/lib/sync.ts b/src/lib/sync.ts
new file mode 100644
index 0000000..7b79e1f
--- /dev/null
+++ b/src/lib/sync.ts
@@ -0,0 +1,72 @@
+import type { Note, Folder } from '../db'
+import { authHeaders } from './auth'
+
+const API = '/api'
+
+export type SyncPayload = { notes: Note[]; folders: Folder[] }
+
+export async function pullAll(): Promise<SyncPayload> {
+  const res = await fetch(`${API}/notes/sync`, { headers: authHeaders() })
+  if (!res.ok) throw new Error('同步失败')
+  return res.json()
+}
+
+export async function pushAll(payload: SyncPayload): Promise<void> {
+  const res = await fetch(`${API}/notes/sync`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json', ...authHeaders() },
+    body: JSON.stringify(payload),
+  })
+  if (!res.ok) throw new Error('推送失败')
+}
+
+export async function pushNote(note: Note): Promise<void> {
+  fetch(`${API}/notes/${note.id}`, {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json', ...authHeaders() },
+    body: JSON.stringify(note),
+  }).catch(() => {})
+}
+
+export async function pushFolder(folder: Folder): Promise<void> {
+  fetch(`${API}/folders/${folder.id}`, {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json', ...authHeaders() },
+    body: JSON.stringify(folder),
+  }).catch(() => {})
+}
+
+export async function pushDeleteNote(id: string): Promise<void> {
+  fetch(`${API}/notes/${id}`, {
+    method: 'DELETE',
+    headers: authHeaders(),
+  }).catch(() => {})
+}
+
+export async function pushDeleteFolder(id: string): Promise<void> {
+  fetch(`${API}/folders/${id}`, {
+    method: 'DELETE',
+    headers: authHeaders(),
+  }).catch(() => {})
+}
+
+export function mergeNotes(local: Note[], remote: Note[]): Note[] {
+  const map = new Map<string, Note>()
+  for (const n of local) map.set(n.id, n)
+  for (const n of remote) {
+    const existing = map.get(n.id)
+    if (!existing || n.updatedAt > existing.updatedAt) {
+      map.set(n.id, { ...n, tags: Array.isArray(n.tags) ? n.tags : JSON.parse(n.tags as any) })
+    }
+  }
+  return Array.from(map.values())
+}
+
+export function mergeFolders(local: Folder[], remote: Folder[]): Folder[] {
+  const map = new Map<string, Folder>()
+  for (const f of local) map.set(f.id, f)
+  for (const f of remote) {
+    if (!map.has(f.id)) map.set(f.id, f)
+  }
+  return Array.from(map.values())
+}