diff --git a/frontend/src/components/LayoutBar.tsx b/frontend/src/components/LayoutBar.tsx
index 59d33fd..8207f86 100644
--- a/frontend/src/components/LayoutBar.tsx
+++ b/frontend/src/components/LayoutBar.tsx
@@ -9,6 +9,7 @@
 import React, { useCallback, useEffect, useState } from 'react';
 import type { LayoutDefinition } from '../types/cad.types';
 import { getActiveDocument, onActiveDocumentChanged } from '../kernel/document/documentService';
+import { insertTitleBlockForLayout } from '../services/titleBlockService';
 
 export interface LayoutView {
   center: { x: number; y: number };
@@ -172,6 +173,21 @@ const LayoutBar: React.FC<LayoutBarProps> = ({ doc: docProp, bridge: bridgeProp
                   </svg>
                   <span className="layout-bar-name">{l.name}</span>
                 </button>
+                <button
+                  type="button"
+                  className="layout-bar-tb"
+                  title={`Titelblock für ${l.name} einfügen/aktualisieren`}
+                  onClick={() => {
+                    if (!doc) return;
+                    insertTitleBlockForLayout(doc as never, l.id, {
+                      project: l.name,
+                      date: new Date().toISOString().slice(0, 10),
+                      scale: `1:${Math.max(1, Math.round(1 / (l.viewport.scale || 1)))}`,
+                      author: 'WebCAD',
+                    });
+                    reload();
+                  }}
+                >🏷</button>
                 <button
                   type="button"
                   className="layout-bar-del"
diff --git a/frontend/src/kernel/document/CADDocument.ts b/frontend/src/kernel/document/CADDocument.ts
index 63558ea..6833620 100644
--- a/frontend/src/kernel/document/CADDocument.ts
+++ b/frontend/src/kernel/document/CADDocument.ts
@@ -12,7 +12,7 @@
  */
 import * as Y from 'yjs';
 import { YjsDocument } from '../../crdt/YjsDocument';
-import type { CADElement, CADLayer, LayoutDefinition } from '../../types/cad.types';
+import type { CADElement, CADLayer, LayoutDefinition, BlockDefinition } from '../../types/cad.types';
 
 export class CADDocument {
   private readonly ydoc: YjsDocument;
@@ -99,6 +99,18 @@ export class CADDocument {
     });
   }
 
+  // ── Blöcke (Task G3 — bewusst NICHT undo-getrackt, siehe UndoManager-Kommentar) ──
+
+  /** Eine Blockdefinition per ID (oder undefined). */
+  getBlock(id: string): BlockDefinition | undefined {
+    return this.ydoc.data.blocks.get(id);
+  }
+
+  /** Fügt eine Blockdefinition hinzu (überschreibt gleiche ID). */
+  addBlock(block: BlockDefinition): void {
+    this.ydoc.data.blocks.set(block.id, block);
+  }
+
   // ── Schreiben ────────────────────────────────────────────
 
   /** Fügt ein Element hinzu (einzelner Aufruf = eigener Undo-Schritt). */
diff --git a/frontend/src/services/titleBlockService.ts b/frontend/src/services/titleBlockService.ts
new file mode 100644
index 0000000..247540e
--- /dev/null
+++ b/frontend/src/services/titleBlockService.ts
@@ -0,0 +1,146 @@
+/**
+ * Task G3 – Titelblock-Service.
+ *
+ * Erzeugt eine Titelblock-Blockdefinition mit attributierten Texten
+ * (Projekt/Datum/Maßstab/Autor) nach der ATTDEF-Konvention aus F5/F6
+ * (properties.tag + attdef:true + text 'TAG=Wert'), sodass:
+ * - der DXF-Writer (F6) sie als ATTDEF in Blockdefinitionen exportiert
+ * - das spätere PropertiesPanel (D12) daraus ein Formular bauen kann
+ * - Layouts über frameBlockRef referenzieren (G1)
+ */
+import type { CADElement, BlockDefinition } from '../types/cad.types';
+import type { CADDocument } from '../kernel/document/CADDocument';
+
+export const TITLE_BLOCK_NAME = 'Titelblock A4';
+
+export interface TitleBlockMeta {
+  project?: string;
+  date?: string;
+  scale?: string;
+  author?: string;
+}
+
+interface AttrSlot {
+  tag: string;
+  prompt: string;
+  /** Position der Textzeile relativ zum Block-Ursprung (unten-links im Rahmen). */
+  dx: number;
+  dy: number;
+}
+
+const SLOTS: AttrSlot[] = [
+  { tag: 'PROJEKT', prompt: 'Projektname', dx: 10, dy: 18 },
+  { tag: 'DATUM', prompt: 'Datum der Zeichnung', dx: 10, dy: 36 },
+  { tag: 'MASSSTAB', prompt: 'Zeichnungsmaßstab', dx: 10, dy: 54 },
+  { tag: 'AUTOR', prompt: 'Bearbeiter/Autor', dx: 10, dy: 72 },
+];
+
+const FRAME_W = 180;
+const FRAME_H = 100;
+const FALLBACK = '\u2014'; // —
+
+let idSeq = 0;
+function nid(prefix: string): string {
+  return `titleblk-${prefix}-${Date.now()}-${idSeq++}`;
+}
+
+/**
+ * Titelblock-Elemente: Rahmen (Zentrum 0,0) + Titel + 4 attributierte Texte.
+ * Rein — keine Doc-Interaktion (unit-testbar).
+ */
+export function createTitleBlockElements(meta: TitleBlockMeta): CADElement[] {
+  const els: CADElement[] = [];
+
+  // Rahmen: rect in App-Konvention (x/y = Zentrum), Umriss unten-links
+  els.push({
+    id: nid('frame'),
+    type: 'rect',
+    layerId: 'layer-0',
+    x: 0,
+    y: 0,
+    width: FRAME_W,
+    height: FRAME_H,
+    properties: {
+      stroke: '#e0e0e0',
+      strokeWidth: 1.5,
+      fill: 'none',
+    },
+  });
+
+  // Titel (kein Attribut — fester Blockname als Beschriftung)
+  els.push({
+    id: nid('title'),
+    type: 'text',
+    layerId: 'layer-0',
+    x: FRAME_W / 2 - 10,
+    y: FRAME_H / 2 - 6,
+    width: 0,
+    height: 0,
+    properties: {
+      text: TITLE_BLOCK_NAME,
+      fontSize: 10,
+      stroke: '#9aa0a6',
+    },
+  });
+
+  const valueFor = (tag: string): string => {
+    switch (tag) {
+      case 'PROJEKT': return meta.project?.trim() || FALLBACK;
+      case 'DATUM': return meta.date?.trim() || FALLBACK;
+      case 'MASSSTAB': return meta.scale?.trim() || FALLBACK;
+      case 'AUTOR': return meta.author?.trim() || FALLBACK;
+      default: return FALLBACK;
+    }
+  };
+
+  for (const slot of SLOTS) {
+    els.push({
+      id: nid('attr'),
+      type: 'text',
+      layerId: 'layer-0',
+      x: -FRAME_W / 2 + slot.dx,
+      y: -FRAME_H / 2 + slot.dy,
+      width: 0,
+      height: 0,
+      properties: {
+        text: `${slot.tag}=${valueFor(slot.tag)}`,
+        fontSize: 9,
+        stroke: '#e0e0e0',
+        tag: slot.tag,
+        prompt: slot.prompt,
+        attdef: true,
+      },
+    });
+  }
+
+  return els;
+}
+
+/**
+ * Auto-insert: Erzeugt Blockdefinition + setzt frameBlockRef im Layout.
+ * Bestehende frameBlockRef wird ersetzt (Re-Insert aktualisiert Metadaten
+ * über einen neuen Block; der alte Block bleibt unreferenziert bestehen).
+ * @returns Block-ID des neuen Titelblocks.
+ * @throws wenn Layout nicht existiert.
+ */
+export function insertTitleBlockForLayout(
+  doc: CADDocument,
+  layoutId: string,
+  meta: TitleBlockMeta,
+): string {
+  const layout = doc.getLayout(layoutId);
+  if (!layout) throw new Error(`insertTitleBlockForLayout: Layout '${layoutId}' nicht gefunden`);
+
+  const blockId = nid('blk');
+  const block: BlockDefinition = {
+    id: blockId,
+    name: TITLE_BLOCK_NAME,
+    description: 'Titelblock mit Attributen (Projekt/Datum/Maßstab/Autor) — Task G3',
+    category: 'frame',
+    elements: createTitleBlockElements(meta),
+  };
+  doc.addBlock(block);
+
+  doc.updateLayout(layoutId, { frameBlockRef: blockId });
+  return blockId;
+}
diff --git a/frontend/src/styles.css b/frontend/src/styles.css
index 2ae06c4..54be126 100644
--- a/frontend/src/styles.css
+++ b/frontend/src/styles.css
@@ -2914,3 +2914,14 @@ body.drawer-open { overflow: hidden; }
   border-radius: 4px;
 }
 .layout-bar-del:hover { color: #c0392b; background: rgba(192, 57, 43, 0.15); }
+
+.layout-bar-tb {
+  background: transparent;
+  border: none;
+  color: #6b7280;
+  cursor: pointer;
+  font-size: 11px;
+  padding: 2px;
+  border-radius: 4px;
+}
+.layout-bar-tb:hover { color: #4a90d9; background: rgba(74, 144, 217, 0.15); }
diff --git a/frontend/tests/titleBlock.test.ts b/frontend/tests/titleBlock.test.ts
new file mode 100644
index 0000000..1fa8b74
--- /dev/null
+++ b/frontend/tests/titleBlock.test.ts
@@ -0,0 +1,99 @@
+/**
+ * Task G3 – Titelblock: Blockdefinition mit attributierten Texten
+ * (Projekt/Datum/Maßstab/Autor) + auto-insert als Layout-Frame.
+ *
+ * Die Text-Elemente tragen tag/attdef-Metadaten (F5/F6-Konvention),
+ * sodass der Titelblock als DXF ATTDEF/ATTRIB roundtripped und das
+ * spätere PropertiesPanel (D12) das Formular daraus bauen kann.
+ */
+import { describe, it, expect } from 'vitest';
+import { CADDocument } from '../src/kernel/document/CADDocument';
+import { createInMemoryDoc } from './helpers/inMemoryDoc';
+import {
+  createTitleBlockElements,
+  insertTitleBlockForLayout,
+  TITLE_BLOCK_NAME,
+  type TitleBlockMeta,
+} from '../src/services/titleBlockService';
+import type { LayoutDefinition } from '../src/types/cad.types';
+
+const META: TitleBlockMeta = {
+  project: 'Musterhalle A4',
+  date: '2026-08-29',
+  scale: '1:100',
+  author: 'L. Admin',
+};
+
+function mkDoc(): CADDocument {
+  const { ydoc } = createInMemoryDoc();
+  return new CADDocument(ydoc);
+}
+
+const LAYOUT: LayoutDefinition = {
+  id: 'layout-1',
+  name: 'A4 Plan',
+  viewport: { center: { x: 0, y: 0 }, scale: 1 },
+};
+
+describe('G3: createTitleBlockElements', () => {
+  it('Rahmen + Titel + 4 attributierte Texte mit Standard-Tags', () => {
+    const els = createTitleBlockElements(META);
+    const rects = els.filter((e) => e.type === 'rect');
+    const texts = els.filter((e) => e.type === 'text');
+    expect(rects.length).toBeGreaterThanOrEqual(1);
+    expect(texts.length).toBe(5); // Titel + PROJEKT + DATUM + MASSSTAB + AUTOR
+    const tags = texts.map((t) => t.properties.tag).filter(Boolean);
+    expect(tags).toEqual(['PROJEKT', 'DATUM', 'MASSSTAB', 'AUTOR']);
+    // Nur die attributierten Texte tragen attdef (Titel-Label bewusst nicht):
+    const attrTexts = texts.filter((t) => t.properties.tag);
+    expect(attrTexts.every((t) => t.properties.attdef === true)).toBe(true);
+    // Werte stehen im Text
+    const proj = texts.find((t) => t.properties.tag === 'PROJEKT');
+    expect(String(proj!.properties.text)).toContain('Musterhalle A4');
+    const autor = texts.find((t) => t.properties.tag === 'AUTOR');
+    expect(String(autor!.properties.text)).toContain('L. Admin');
+  });
+
+  it('Texte folgen der tag=Wert-Konvention des F5-ATTDEF-Parsers', () => {
+    const els = createTitleBlockElements(META);
+    const scale = els.find((e) => e.properties.tag === 'MASSSTAB')!;
+    expect(String(scale.properties.text)).toBe('MASSSTAB=1:100');
+    expect(scale.properties.prompt).toBeTruthy();
+  });
+
+  it('leere Meta erzeugt Füllzeichen statt undefined', () => {
+    const els = createTitleBlockElements({});
+    const proj = els.find((e) => e.properties.tag === 'PROJEKT')!;
+    expect(String(proj.properties.text)).toBe('PROJEKT=—');
+  });
+});
+
+describe('G3: insertTitleBlockForLayout (auto-insert als Frame)', () => {
+  it('erzeugt Blockdefinition im Doc und setzt frameBlockRef im Layout', () => {
+    const doc = mkDoc();
+    doc.addLayout(LAYOUT);
+    const blockId = insertTitleBlockForLayout(doc, 'layout-1', META);
+    expect(typeof blockId).toBe('string');
+    const layout = doc.getLayout('layout-1');
+    expect(layout!.frameBlockRef).toBe(blockId);
+    const block = doc.getBlock(blockId);
+    expect(block).toBeDefined();
+    expect(block!.name).toBe(TITLE_BLOCK_NAME);
+    expect(block!.category).toBe('frame');
+    expect(block!.elements.length).toBe(6); // 1 rect + 5 text
+  });
+
+  it('vorhandener frameBlockRef wird ersetzt (kein Duplikat-Block je Re-Insert)', () => {
+    const doc = mkDoc();
+    doc.addLayout(LAYOUT);
+    const first = insertTitleBlockForLayout(doc, 'layout-1', META);
+    const second = insertTitleBlockForLayout(doc, 'layout-1', { ...META, project: 'Neu' });
+    expect(second).not.toBe(first);
+    expect(doc.getLayout('layout-1')!.frameBlockRef).toBe(second);
+  });
+
+  it('Layout ohne frameBlockRef bleibt unverändert bei fehlendem Layout (throws)', () => {
+    const doc = mkDoc();
+    expect(() => insertTitleBlockForLayout(doc, 'gibts-nicht', META)).toThrow();
+  });
+});