diff --git a/backend/src/auth/authMiddleware.ts b/backend/src/auth/authMiddleware.ts
index dbb8aaf..69f549a 100644
--- a/backend/src/auth/authMiddleware.ts
+++ b/backend/src/auth/authMiddleware.ts
@@ -44,3 +44,20 @@ export function requireAdmin(request: FastifyRequest, reply: FastifyReply, authS
   }
   return user;
 }
+
+/**
+ * Require library-admin role (Task H3: global library write guard).
+ * Library-admin is bound to the existing admin role: only admins may
+ * write (create/update/delete/import) the GLOBAL block library, while
+ * every authenticated user may read/export it. Own drawing-scoped
+ * blocks are unaffected (per-user ownership there).
+ */
+export function requireLibraryAdmin(request: FastifyRequest, reply: FastifyReply, authService: AuthService): DBUser | null {
+  const user = requireAuth(request, reply, authService);
+  if (!user) return null;
+  if (user.role !== 'admin') {
+    reply.code(403).send({ error: 'Library admin access required' });
+    return null;
+  }
+  return user;
+}
diff --git a/backend/src/routes/globalBlocks.ts b/backend/src/routes/globalBlocks.ts
index 720003c..62172ab 100644
--- a/backend/src/routes/globalBlocks.ts
+++ b/backend/src/routes/globalBlocks.ts
@@ -3,7 +3,7 @@
  */
 import type { FastifyInstance } from 'fastify';
 import type { DatabaseInterface } from '../database/DatabaseInterface.js';
-import { requireAuth } from '../auth/authMiddleware.js';
+import { requireAuth, requireLibraryAdmin } from '../auth/authMiddleware.js';
 import type { AuthService } from '../auth/AuthService.js';
 import { validateName, validateIdParam } from '../utils/validation.js';
 import JSZip from 'jszip';
@@ -36,7 +36,7 @@ export function registerGlobalBlockRoutes(fastify: FastifyInstance, db: Database
 
   // Create a new folder
   fastify.post('/api/global-folders', async (request, reply) => {
-    if (!requireAuth(request, reply, authService)) return;
+    if (!requireLibraryAdmin(request, reply, authService)) return;
     const body = request.body as { name?: string; parent_id?: string | null };
     const nameErr = validateName(body.name, 'name');
     if (nameErr) return reply.code(400).send({ error: nameErr });
@@ -49,7 +49,7 @@ export function registerGlobalBlockRoutes(fastify: FastifyInstance, db: Database
 
   // Rename / move a folder
   fastify.patch('/api/global-folders/:id', async (request, reply) => {
-    if (!requireAuth(request, reply, authService)) return;
+    if (!requireLibraryAdmin(request, reply, authService)) return;
     const { id } = request.params as { id: string };
     const idErr = validateIdParam(id, 'id');
     if (idErr) return reply.code(400).send({ error: idErr });
@@ -71,7 +71,7 @@ export function registerGlobalBlockRoutes(fastify: FastifyInstance, db: Database
 
   // Delete a folder (cascades to children, blocks get folder_id = NULL)
   fastify.delete('/api/global-folders/:id', async (request, reply) => {
-    if (!requireAuth(request, reply, authService)) return;
+    if (!requireLibraryAdmin(request, reply, authService)) return;
     const { id } = request.params as { id: string };
     const idErr = validateIdParam(id, 'id');
     if (idErr) return reply.code(400).send({ error: idErr });
@@ -107,7 +107,7 @@ export function registerGlobalBlockRoutes(fastify: FastifyInstance, db: Database
 
   // Create a new global block
   fastify.post('/api/global-blocks', async (request, reply) => {
-    if (!requireAuth(request, reply, authService)) return;
+    if (!requireLibraryAdmin(request, reply, authService)) return;
     const body = request.body as { name?: string; folder_id?: string | null; block_data?: string; svg_data?: string };
     const nameErr = validateName(body.name, 'name');
     if (nameErr) return reply.code(400).send({ error: nameErr });
@@ -131,7 +131,7 @@ export function registerGlobalBlockRoutes(fastify: FastifyInstance, db: Database
 
   // Update a global block (rename, move, update data)
   fastify.patch('/api/global-blocks/:id', async (request, reply) => {
-    if (!requireAuth(request, reply, authService)) return;
+    if (!requireLibraryAdmin(request, reply, authService)) return;
     const { id } = request.params as { id: string };
     const idErr = validateIdParam(id, 'id');
     if (idErr) return reply.code(400).send({ error: idErr });
@@ -160,7 +160,7 @@ export function registerGlobalBlockRoutes(fastify: FastifyInstance, db: Database
 
   // Delete a global block
   fastify.delete('/api/global-blocks/:id', async (request, reply) => {
-    if (!requireAuth(request, reply, authService)) return;
+    if (!requireLibraryAdmin(request, reply, authService)) return;
     const { id } = request.params as { id: string };
     const idErr = validateIdParam(id, 'id');
     if (idErr) return reply.code(400).send({ error: idErr });
@@ -192,7 +192,7 @@ export function registerGlobalBlockRoutes(fastify: FastifyInstance, db: Database
 
   // Import: .wcadlib-Paket einspielen (IDs neu, Ordner-Hierarchie über Mapping erhalten)
   fastify.post('/api/global-blocks/import', async (request, reply) => {
-    if (!requireAuth(request, reply, authService)) return;
+    if (!requireLibraryAdmin(request, reply, authService)) return;
     const pkg = request.body as {
       format?: string;
       folders?: Array<{ id: string; name: string; parent_id: string | null }>;
@@ -280,7 +280,7 @@ export function registerGlobalBlockRoutes(fastify: FastifyInstance, db: Database
 
   // ZIP-Import: .wcadlib-ZIP einspielen (Ordner-Mapping, Blöcke, Thumbnails)
   fastify.post('/api/global-blocks/import-zip', async (request, reply) => {
-    if (!requireAuth(request, reply, authService)) return;
+    if (!requireLibraryAdmin(request, reply, authService)) return;
     const body = request.body;
     if (!Buffer.isBuffer(body) || body.length === 0) {
       return reply.code(400).send({ error: 'ZIP body fehlt oder leer' });
diff --git a/backend/tests/libraryAdminGuard.test.ts b/backend/tests/libraryAdminGuard.test.ts
new file mode 100644
index 0000000..c2bcead
--- /dev/null
+++ b/backend/tests/libraryAdminGuard.test.ts
@@ -0,0 +1,160 @@
+/**
+ * Task H3 – Rollen: library-admin (global write) vs. user (read-only).
+ *
+ * requireLibraryAdmin schützt alle schreibenden Global-Library-Routen:
+ * POST/PATCH/DELETE auf folders+blocks, import, import-zip. Lesen
+ * (GET, export) bleibt für alle authentifizierten Nutzer offen.
+ * library-admin ist an die bestehende admin-Rolle angebunden.
+ */
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import type { FastifyInstance } from 'fastify';
+import { SqliteAdapter } from '../src/database/SqliteAdapter.js';
+import { createServer } from '../src/server.js';
+
+describe('Task H3: library-admin Guard', () => {
+  let app: FastifyInstance;
+  let db: SqliteAdapter;
+  let adminToken: string;
+  let planerToken: string;
+
+  beforeAll(async () => {
+    db = new SqliteAdapter(':memory:');
+    await db.init();
+    app = await createServer({ db, port: 0 });
+    await app.ready();
+
+    const adminReg = await app.inject({
+      method: 'POST',
+      url: '/api/auth/register',
+      payload: { email: 'h3-admin@example.com', password: 'Password123!', name: 'H3 Admin', role: 'admin' },
+    });
+    if (adminReg.statusCode !== 201) console.error('ADMIN REG FAILED:', adminReg.statusCode, adminReg.body.slice(0, 200));
+    adminToken = JSON.parse(adminReg.body).session?.token ?? '';
+
+    const planerReg = await app.inject({
+      method: 'POST',
+      url: '/api/auth/register',
+      payload: { email: 'h3-planer@example.com', password: 'Password123!', name: 'H3 Planer', role: 'planer' },
+    });
+    if (planerReg.statusCode !== 201) console.error('PLANER REG FAILED:', planerReg.statusCode, planerReg.body.slice(0, 200));
+    planerToken = JSON.parse(planerReg.body).session?.token ?? '';
+    admin = { authorization: `Bearer ${adminToken}` };
+    planer = { authorization: `Bearer ${planerToken}` };
+  });
+
+  afterAll(async () => {
+    await app.close();
+    db.close();
+  });
+
+  // WICHTIG: Header-Objekte werden in beforeAll gebaut — der describe-Body
+  // läuft VOR den Hooks, Template-Literale würden undefined capturen.
+  let planer: Record<string, string>;
+  let admin: Record<string, string>;
+
+  // ── Lesen bleibt offen (beide Rollen) ──
+
+  it('planer kann globale Ordner LESEN (200)', async () => {
+    const res = await app.inject({ method: 'GET', url: '/api/global-folders', headers: planer });
+    expect(res.statusCode).toBe(200);
+  });
+
+  it('planer kann globale Blöcke LESEN (200)', async () => {
+    const res = await app.inject({ method: 'GET', url: '/api/global-blocks', headers: planer });
+    expect(res.statusCode).toBe(200);
+  });
+
+  it('planer kann Library EXPORTIEREN (GET export, 200)', async () => {
+    const res = await app.inject({ method: 'GET', url: '/api/global-blocks/export', headers: planer });
+    expect(res.statusCode).toBe(200);
+  });
+
+  // ── Schreiben nur für library-admin (admin-Rolle) ──
+
+  it('planer POST /api/global-folders → 403', async () => {
+    const res = await app.inject({
+      method: 'POST', url: '/api/global-folders', headers: planer,
+      payload: { name: 'Verboten', parent_id: null },
+    });
+    expect(res.statusCode).toBe(403);
+    expect(JSON.parse(res.body).error).toContain('Library');
+  });
+
+  it('planer POST /api/global-blocks → 403', async () => {
+    const res = await app.inject({
+      method: 'POST', url: '/api/global-blocks', headers: planer,
+      payload: { name: 'Verboten', block_data: '[]' },
+    });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it('planer PATCH /api/global-folders/:id → 403', async () => {
+    const res = await app.inject({
+      method: 'PATCH', url: '/api/global-folders/irgendeine-id', headers: planer,
+      payload: { name: 'Hack' },
+    });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it('planer PATCH /api/global-blocks/:id → 403', async () => {
+    const res = await app.inject({
+      method: 'PATCH', url: '/api/global-blocks/irgendeine-id', headers: planer,
+      payload: { name: 'Hack' },
+    });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it('planer DELETE /api/global-folders/:id → 403', async () => {
+    const res = await app.inject({ method: 'DELETE', url: '/api/global-folders/irgendeine-id', headers: planer });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it('planer DELETE /api/global-blocks/:id → 403', async () => {
+    const res = await app.inject({ method: 'DELETE', url: '/api/global-blocks/irgendeine-id', headers: planer });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it('planer POST /api/global-blocks/import → 403', async () => {
+    const res = await app.inject({
+      method: 'POST', url: '/api/global-blocks/import', headers: planer,
+      payload: { format: 'wcadlib', blocks: [] },
+    });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it('planer POST /api/global-blocks/import-zip → 403', async () => {
+    const res = await app.inject({
+      method: 'POST', url: '/api/global-blocks/import-zip', headers: { ...planer, 'content-type': 'application/zip' },
+      payload: Buffer.from('PK'),
+    });
+    expect(res.statusCode).toBe(403);
+  });
+
+  // ── Admin (library-admin) darf schreiben ──
+
+  it('admin POST /api/global-folders → 201 (write erlaubt)', async () => {
+    const res = await app.inject({
+      method: 'POST', url: '/api/global-folders', headers: admin,
+      payload: { name: 'Admin Set', parent_id: null },
+    });
+    expect(res.statusCode).toBe(201);
+  });
+
+  it('admin POST /api/global-blocks → 201 (write erlaubt)', async () => {
+    const res = await app.inject({
+      method: 'POST', url: '/api/global-blocks', headers: admin,
+      payload: { name: 'Admin Block', block_data: '[]', folder_id: null },
+    });
+    expect(res.statusCode).toBe(201);
+  });
+
+  // ── Unauthentifiziert bleibt 401 ──
+
+  it('ohne Token POST /api/global-folders → 401 (nicht 403)', async () => {
+    const res = await app.inject({
+      method: 'POST', url: '/api/global-folders',
+      payload: { name: 'Anon', parent_id: null },
+    });
+    expect(res.statusCode).toBe(401);
+  });
+});