diff --git a/frontend/src/components/PropertiesPanel.tsx b/frontend/src/components/PropertiesPanel.tsx
index ee14b9e..ed21985 100644
--- a/frontend/src/components/PropertiesPanel.tsx
+++ b/frontend/src/components/PropertiesPanel.tsx
@@ -3,6 +3,7 @@ import { polygonArea } from '../tools/modification/geometry';
 import { formatArea } from '../utils/format';
 import type { PropertiesPanelProps } from '../types/ui.types';
 import { formatInputValue, parseDistance, type UnitType } from '../utils/format';
+import { getActiveDocument } from '../kernel/document/documentService';
 
 const parseNum = (s: string) => parseFloat(s.replace(/[^0-9.\-]/g, '')) || 0;
 
@@ -77,7 +78,37 @@ const PropertiesPanel: React.FC<PropertiesPanelProps> = ({
             <label className="prop-label">Fläche</label>
             <span className="prop-value">{formatArea(polygonArea(el.properties.points as Array<{ x: number; y: number }>), unit, scaleFactor)}</span>
           </div>
-        )}` : ''}</span>
+        )}
+
+        {/* ─── Task D12: Block-Attribute-Formular (block_instance) ─── */}
+        {el.type === 'block_instance' && (() => {
+          const blockId = el.properties.blockId as string | undefined;
+          if (!blockId) return null;
+          const block = getActiveDocument()?.getBlock(blockId);
+          const attrDefs = block?.attrDefs ?? [];
+          if (attrDefs.length === 0) return null;
+          const attrValues = (el.properties.attrValues as Record<string, string> | undefined) ?? {};
+          return (
+            <div className="panel-section">
+              <div className="panel-section-title">Block-Attribute</div>
+              {attrDefs.map((def) => (
+                <div className="prop-row" key={def.tag}>
+                  <label className="prop-label" title={def.prompt}>{def.tag}</label>
+                  <input
+                    className="prop-input"
+                    type="text"
+                    value={attrValues[def.tag] ?? def.defaultValue ?? ''}
+                    placeholder={def.prompt}
+                    onChange={(ev) => {
+                      const next = { ...attrValues, [def.tag]: ev.target.value };
+                      onUpdateProperty('attrValues', next);
+                    }}
+                  />
+                </div>
+              ))}
+            </div>
+          );
+        })()}` : ''}</span>
           <div style={{ display: 'flex', gap: '4px' }}>
             {onDelete && el && (
               <button
diff --git a/frontend/src/render/pixi/elementDrawers.ts b/frontend/src/render/pixi/elementDrawers.ts
index 7e42cfd..2015128 100644
--- a/frontend/src/render/pixi/elementDrawers.ts
+++ b/frontend/src/render/pixi/elementDrawers.ts
@@ -42,7 +42,7 @@ function fillOrNull(raw: unknown): string | null {
  * Gibt ein leeres Array zurück für unbekannte Typen bzw. Elemente,
  * die nichts Sichtbares beitragen (z.B. leerer Text).
  */
-export function elementToPrimitives(el: CADElement): ShapePrimitive[] {
+export function elementToPrimitives(el: CADElement, attrDefs?: Array<{ tag: string; prompt: string; defaultValue?: string }>): ShapePrimitive[] {
   const props = (el.properties ?? {}) as Record<string, unknown>;
   const stroke = (props.stroke as string | undefined) ?? FALLBACK_STROKE;
   const sw = (props.strokeWidth as number | undefined) ?? 1;
@@ -296,6 +296,28 @@ export function elementToPrimitives(el: CADElement): ShapePrimitive[] {
       return out;
     }
 
+    case 'block_instance': {
+      // Task D12: Attr-Texte der Instanz zeichnen (tag=Wert, default-Fallback).
+      const attrValues = (props.attrValues as Record<string, string> | undefined) ?? {};
+      if (!attrDefs || attrDefs.length === 0) return [];
+      const out: ShapePrimitive[] = [];
+      const fontSize = 9;
+      const lineH = 16;
+      let i = 0;
+      for (const def of attrDefs) {
+        const value = attrValues[def.tag] ?? def.defaultValue ?? '—';
+        out.push({
+          kind: 'text',
+          at: { x: el.x, y: el.y - 8 - i * lineH },
+          text: `${def.tag}=${value}`,
+          fontSize,
+          color: stroke,
+        });
+        i++;
+      }
+      return out;
+    }
+
     default:
       return [];
   }
diff --git a/frontend/src/types/cad.types.ts b/frontend/src/types/cad.types.ts
index 9e89b1b..c0cccdb 100644
--- a/frontend/src/types/cad.types.ts
+++ b/frontend/src/types/cad.types.ts
@@ -63,6 +63,16 @@ export interface ImageElement extends CADElement {
   };
 }
 
+/**
+ * Block-Attribut-Definition (Task D12): Slot, den Instanzen befüllen.
+ * Konvention konsistent zu F5 (ATTDEF-Parser) und F6 (DXF-Writer).
+ */
+export interface BlockAttrDef {
+  tag: string;
+  prompt: string;
+  defaultValue?: string;
+}
+
 export interface BlockDefinition {
   id: string;
   name: string;
@@ -70,6 +80,8 @@ export interface BlockDefinition {
   category: string;
   elements: CADElement[];
   thumbnail?: string;
+  /** Attribut-Slots dieser Blockdefinition (Task D12). */
+  attrDefs?: BlockAttrDef[];
 }
 
 /**
diff --git a/frontend/tests/blockAttributes.test.ts b/frontend/tests/blockAttributes.test.ts
new file mode 100644
index 0000000..617114d
--- /dev/null
+++ b/frontend/tests/blockAttributes.test.ts
@@ -0,0 +1,104 @@
+/**
+ * Task D12 - BlockAttribute: attrDefs + attrValues + Rendering.
+ *
+ * BlockDefinition.attrDefs[]: definiert Attribut-Slots (tag/prompt/
+ * default). Instanz (block_instance) traegt attrValues. Der Render-
+ * Adapter (elementToPrimitives) zeichnet die Attr-Werte als Text-
+ * Primitive an der Instanz-Position.
+ */
+import { describe, it, expect } from 'vitest';
+import { CADDocument } from '../src/kernel/document/CADDocument';
+import { createInMemoryDoc } from './helpers/inMemoryDoc';
+import { elementToPrimitives } from '../src/render/pixi/elementDrawers';
+import type { CADElement, BlockDefinition } from '../src/types/cad.types';
+
+const BLOCK: BlockDefinition = {
+  id: 'blk-1',
+  name: 'Titelblock',
+  description: '',
+  category: 'frame',
+  elements: [],
+  attrDefs: [
+    { tag: 'PROJEKT', prompt: 'Projektname', defaultValue: 'Unbenannt' },
+    { tag: 'AUTOR', prompt: 'Bearbeiter', defaultValue: 'WebCAD' },
+  ],
+};
+
+function instance(attrValues: Record<string, string>): CADElement {
+  return {
+    id: 'inst-1', type: 'block_instance', layerId: 'layer-0',
+    x: 100, y: 100, width: 0, height: 0,
+    properties: { blockId: 'blk-1', scale: 1, attrValues },
+  } as unknown as CADElement;
+}
+
+// ─── Typ-Ebene: attrDefs auf BlockDefinition ────────────────
+
+describe('D12: BlockDefinition.attrDefs', () => {
+  it('attrDefs-Feld existiert mit tag/prompt/defaultValue', () => {
+    expect(BLOCK.attrDefs).toBeDefined();
+    expect(BLOCK.attrDefs!.length).toBe(2);
+    expect(BLOCK.attrDefs![0].tag).toBe('PROJEKT');
+    expect(BLOCK.attrDefs![0].prompt).toBe('Projektname');
+    expect(BLOCK.attrDefs![0].defaultValue).toBe('Unbenannt');
+  });
+
+  it('CADDocument speichert Block mit attrDefs (getBlock liefert sie zurueck)', () => {
+    const { ydoc } = createInMemoryDoc();
+    const doc = new CADDocument(ydoc);
+    doc.addBlock(BLOCK);
+    const loaded = doc.getBlock('blk-1');
+    expect(loaded!.attrDefs).toHaveLength(2);
+    expect(loaded!.attrDefs![1].tag).toBe('AUTOR');
+  });
+});
+
+// ─── Rendering: elementToPrimitives mit attrDefs ────────────
+
+describe('D12: RenderAdapter zeichnet Attr-Texte', () => {
+  it('Instanz mit attrValues erzeugt text-Primitives pro Attribut', () => {
+    const el = instance({ PROJEKT: 'Halle A', AUTOR: 'L. Admin' });
+    const prims = elementToPrimitives(el, BLOCK.attrDefs);
+    const texts = prims.filter((p) => p.kind === 'text');
+    expect(texts).toHaveLength(2);
+    const proj = texts.find((t) => (t as { text: string }).text.includes('PROJEKT'));
+    expect(proj).toBeDefined();
+    expect((proj as { text: string }).text).toContain('Halle A');
+    const autor = texts.find((t) => (t as { text: string }).text.includes('AUTOR'));
+    expect((autor as { text: string }).text).toContain('L. Admin');
+  });
+
+  it('Fehlender Wert faellt auf attrDefs.defaultValue zurueck', () => {
+    const el = instance({});
+    const prims = elementToPrimitives(el, BLOCK.attrDefs);
+    const texts = prims.filter((p) => p.kind === 'text');
+    const proj = texts.find((t) => (t as { text: string }).text.includes('PROJEKT'));
+    expect((proj as { text: string }).text).toContain('Unbenannt');
+  });
+
+  it('Ohne attrDefs-Parameter: kein Attr-Text-Rendering (abwaertskompatibel)', () => {
+    const el = instance({ PROJEKT: 'Halle A' });
+    const prims = elementToPrimitives(el);
+    expect(prims.filter((p) => p.kind === 'text')).toHaveLength(0);
+  });
+
+  it('Instanz ohne attrValues mit attrDefs: defaults werden gezeichnet', () => {
+    const el: CADElement = {
+      id: 'inst-2', type: 'block_instance', layerId: 'layer-0',
+      x: 0, y: 0, width: 0, height: 0,
+      properties: { blockId: 'blk-1', scale: 1 },
+    } as unknown as CADElement;
+    const prims = elementToPrimitives(el, BLOCK.attrDefs);
+    const texts = prims.filter((p) => p.kind === 'text');
+    expect(texts).toHaveLength(2);
+  });
+
+  it('Text-Positionen gestaffelt unterhalb der Instanz-Position', () => {
+    const el = instance({ PROJEKT: 'A', AUTOR: 'B' });
+    const prims = elementToPrimitives(el, BLOCK.attrDefs);
+    const texts = prims.filter((p) => p.kind === 'text') as Array<{ kind: 'text'; at: { x: number; y: number }; text: string }>;
+    expect(texts[0].at.x).toBe(100);
+    expect(texts[0].at.y).toBeCloseTo(100 - 8, 0);
+    expect(texts[1].at.y).toBeLessThan(texts[0].at.y);
+  });
+});