diff --git a/frontend/src/plugins/builtin/core-drawing/index.ts b/frontend/src/plugins/builtin/core-drawing/index.ts
index 65cd217..62677ab 100644
--- a/frontend/src/plugins/builtin/core-drawing/index.ts
+++ b/frontend/src/plugins/builtin/core-drawing/index.ts
@@ -558,15 +558,119 @@ export const ellipseTool: ToolExtensionV2 = {
   },
 };
 
+// ─────────────────────────────────────────────────────────────
+// Task D2: Spline (CV-basiert) — Kontrollpunkt-Klick-Sequenz,
+// ENTER committet ab 3 CVs. Catmull-Rom-Interpolation (Kurve läuft
+// DURCH alle CVs, schwingt an Ecken = echte Glättung).
+// ─────────────────────────────────────────────────────────────
+
+let splinePoints: Pt[] = [];
+
+/**
+ * Catmull-Rom-Spline-Interpolation: Für n CVs werden n-1 Segmente
+ * mit je SEG Samples erzeugt. Tangenten aus Nachbarn (Endpunkte
+ * geklemmt). Ergibt eine glatte Kurve durch alle CVs.
+ */
+function catmullRom(cvs: Pt[], seg = 16): Pt[] {
+  if (cvs.length < 2) return [...cvs];
+  const out: Pt[] = [];
+  const n = cvs.length;
+  for (let i = 0; i < n - 1; i++) {
+    const p0 = cvs[Math.max(0, i - 1)];
+    const p1 = cvs[i];
+    const p2 = cvs[i + 1];
+    const p3 = cvs[Math.min(n - 1, i + 2)];
+    for (let s = (i === 0 ? 0 : 1); s <= seg; s++) {
+      const t = s / seg;
+      const t2 = t * t;
+      const t3 = t2 * t;
+      const x = 0.5 * ((2 * p1.x) + (-p0.x + p2.x) * t + (2 * p0.x - 5 * p1.x + 4 * p2.x - p3.x) * t2 + (-p0.x + 3 * p1.x - 3 * p2.x + p3.x) * t3);
+      const y = 0.5 * ((2 * p1.y) + (-p0.y + p2.y) * t + (2 * p0.y - 5 * p1.y + 4 * p2.y - p3.y) * t2 + (-p0.y + 3 * p1.y - 3 * p2.y + p3.y) * t3);
+      out.push({ x, y });
+    }
+  }
+  return out;
+}
+
+function buildSpline(cvs: Pt[], ctx: FullToolContext): CADElement {
+  const stroke = (ctx.options.strokeColor as string | undefined) ?? '#e0e0f0';
+  const layerId = (ctx.options.layerId as string | undefined) ?? 'layer-0';
+  const pts = catmullRom(cvs);
+  const xs = pts.map((p) => p.x), ys = pts.map((p) => p.y);
+  const minX = Math.min(...xs), minY = Math.min(...ys);
+  const maxX = Math.max(...xs), maxY = Math.max(...ys);
+  return {
+    id: uid('spline'),
+    type: 'polyline',
+    layerId,
+    x: minX + (maxX - minX) / 2,
+    y: minY + (maxY - minY) / 2,
+    width: maxX - minX,
+    height: maxY - minY,
+    properties: {
+      points: pts,
+      controlPoints: [...cvs],
+      stroke,
+      strokeWidth: 1,
+    },
+  } as unknown as CADElement;
+}
+
+export const splineTool: ToolExtensionV2 = {
+  manifest: {
+    id: 'spline',
+    label: 'Spline',
+    icon: '\u2248',
+    ribbonTab: 'canvas',
+    tags: ['basic'],
+    description: 'Spline zeichnen: Kontrollpunkte klicken, ENTER beendet',
+  },
+  optionsSchema: [{ key: 'strokeColor', label: 'Farbe', type: 'color' }],
+  handlers: {
+    down(e, ctx) {
+      splinePoints.push(e.world);
+      ctx.setStatus(`Spline: ${splinePoints.length} Kontrollpunkte – ENTER beendet`);
+    },
+    move(e, ctx) {
+      const c = ctx as FullToolContext;
+      if (splinePoints.length === 0) return;
+      const pts = [...splinePoints, e.world];
+      ctx.setPreview?.(buildSpline(pts, c));
+    },
+    up() { /* commit nur via ENTER */ },
+    key(e, ctx) {
+      if (e.key !== 'Enter' && e.key !== 'ENTER') return false;
+      const c = ctx as FullToolContext;
+      if (splinePoints.length < 3) {
+        ctx.setStatus(`Spline benötigt mindestens 3 Kontrollpunkte (aktuell ${splinePoints.length})`);
+        return true;
+      }
+      if (!c.doc) return false;
+      const el = buildSpline(splinePoints, c);
+      c.doc.transact(() => c.doc!.addElement(el));
+      const count = splinePoints.length;
+      splinePoints = [];
+      ctx.setPreview?.(null);
+      ctx.setStatus(`Spline erstellt (${count} CVs, ${el.id})`);
+      return true;
+    },
+    cancel(ctx) {
+      splinePoints = [];
+      ctx.setPreview?.(null);
+      ctx.setStatus('Spline abgebrochen');
+    },
+  },
+};
+
 export const coreDrawingPlugin: PluginV2 = {
   manifest: {
     id: 'core-drawing',
     name: 'Zeichnen (Kern)',
-    version: '1.3.0',
+    version: '1.4.0',
     author: 'web-cad team',
     description: 'Zeichenwerkzeuge V2: Linie, Rechteck, Kreis, Bogen, Polylinie, Polygon, RevCloud.',
     category: 'tools',
     enabledByDefault: true,
   },
-  tools: [lineTool, rectTool, circleTool, arcTool, polylineTool, polygonTool, revcloudTool, ellipseTool],
+  tools: [lineTool, rectTool, circleTool, arcTool, polylineTool, polygonTool, revcloudTool, ellipseTool, splineTool],
 };
diff --git a/frontend/tests/splineTool.test.ts b/frontend/tests/splineTool.test.ts
new file mode 100644
index 0000000..f12842b
--- /dev/null
+++ b/frontend/tests/splineTool.test.ts
@@ -0,0 +1,147 @@
+/**
+ * Task D2 – Spline-Tool (CV-basiert): Kontrollpunkt-Klick-Sequenz,
+ * ENTER committet ab 3 CVs. Render als interpolierte Polyline mit
+ * Catmull-Rom-Glättung (Kurve läuft DURCH alle CVs), CVs in
+ * properties.controlPoints gespeichert (DXF-SPLINE-Export-ready).
+ */
+import { describe, it, expect, beforeEach } from 'vitest';
+import { splineTool } from '../src/plugins/builtin/core-drawing';
+import { CADDocument } from '../src/kernel/document/CADDocument';
+import { createInMemoryDoc } from './helpers/inMemoryDoc';
+import type { CADElement, Pt } from '../src/types/cad.types';
+
+function mkCtx(options: Record<string, unknown> = {}) {
+  const { ydoc } = createInMemoryDoc();
+  const doc = new CADDocument(ydoc);
+  const previews: (CADElement | null)[] = [];
+  const statuses: string[] = [];
+  const ctx: any = {
+    doc,
+    options,
+    setStatus: (m: string) => statuses.push(m),
+    setPreview: (el: CADElement | null) => previews.push(el),
+  };
+  return { ctx, doc, previews, statuses };
+}
+
+function pe(x: number, y: number): { world: Pt } {
+  return { world: { x, y } } as never;
+}
+
+beforeEach(() => {
+  splineTool.handlers.cancel?.({ setStatus: () => {}, setPreview: () => {} } as never);
+});
+
+describe('D2: splineTool', () => {
+  it('4 CVs + ENTER erzeugt EINE geglaettete Polyline mit mehr Punkten als CVs', () => {
+    const { ctx, doc } = mkCtx();
+    const cvs = [[0, 0], [100, 100], [200, 0], [300, 100]];
+    for (const [x, y] of cvs) splineTool.handlers.down!(pe(x, y), ctx);
+    const committed = splineTool.handlers.key!({ key: 'Enter' } as never, ctx);
+    expect(committed).toBe(true);
+    const els = doc.getAllElements();
+    expect(els).toHaveLength(1);
+    const el = els[0];
+    expect(el.type).toBe('polyline');
+    const pts = el.properties.points as Pt[];
+    expect(pts.length).toBeGreaterThan(8); // geglaettet, nicht nur CVs
+  });
+
+  it('Kurve interpoliert DURCH die CVs: Start/Ende exakt, Zwischen-CVs liegen auf der Kurve', () => {
+    const { ctx, doc } = mkCtx();
+    for (const [x, y] of [[0, 0], [100, 100], [200, 0], [300, 100]]) {
+      splineTool.handlers.down!(pe(x, y), ctx);
+    }
+    splineTool.handlers.key!({ key: 'Enter' } as never, ctx);
+    const el = doc.getAllElements()[0];
+    const pts = el.properties.points as Pt[];
+    expect(pts[0]).toEqual({ x: 0, y: 0 });
+    const last = pts[pts.length - 1];
+    expect(last.x).toBeCloseTo(300, 5);
+    expect(last.y).toBeCloseTo(100, 5);
+    // Zwischenpunkt (100,100) muss auf der Kurve liegen (Catmull-Rom interpoliert):
+    const near = pts.find((p) => Math.abs(p.x - 100) < 1.5 && Math.abs(p.y - 100) < 1.5);
+    expect(near).toBeDefined();
+  });
+
+  it('CVs werden in properties.controlPoints gespeichert', () => {
+    const { ctx, doc } = mkCtx();
+    for (const [x, y] of [[0, 0], [50, 80], [120, 40]]) {
+      splineTool.handlers.down!(pe(x, y), ctx);
+    }
+    splineTool.handlers.key!({ key: 'Enter' } as never, ctx);
+    const el = doc.getAllElements()[0];
+    const cvs = el.properties.controlPoints as Pt[];
+    expect(cvs).toHaveLength(3);
+    expect(cvs[1]).toEqual({ x: 50, y: 80 });
+  });
+
+  it('Glättung: Kurve weicht von der CV-Sehnen-Linie ab (keine Polyline durch CVs)', () => {
+    const { ctx, doc } = mkCtx();
+    // S-artige CVs: (0,0) (0,100) (100,100) (100,0) — Catmull-Rom schwingt um die Ecken
+    for (const [x, y] of [[0, 0], [0, 100], [100, 100], [100, 0]]) {
+      splineTool.handlers.down!(pe(x, y), ctx);
+    }
+    splineTool.handlers.key!({ key: 'Enter' } as never, ctx);
+    const el = doc.getAllElements()[0];
+    const pts = el.properties.points as Pt[];
+    // Es muss Punkte geben, die ausserhalb der BBox der Sehnen-Verbindung liegen
+    // (Glattung schwingt): minY < 0 oder maxY > 100 an irgendeiner Stelle
+    const ys = pts.map((p) => p.y);
+    const swingsBelow = Math.min(...ys) < -0.5;
+    const swingsAbove = Math.max(...ys) > 100.5;
+    expect(swingsBelow || swingsAbove).toBe(true);
+  });
+
+  it('ENTER mit weniger als 3 CVs committet NICHT (Status erklaert Mindestzahl)', () => {
+    const { ctx, doc, statuses } = mkCtx();
+    splineTool.handlers.down!(pe(0, 0), ctx);
+    splineTool.handlers.down!(pe(50, 50), ctx);
+    const consumed = splineTool.handlers.key!({ key: 'Enter' } as never, ctx);
+    expect(doc.getAllElements()).toHaveLength(0);
+    expect(statuses[statuses.length - 1]).toContain('3');
+  });
+
+  it('Nicht-ENTER-Keys werden nicht konsumiert (return false)', () => {
+    const { ctx } = mkCtx();
+    splineTool.handlers.down!(pe(0, 0), ctx);
+    const consumed = splineTool.handlers.key!({ key: 'a' } as never, ctx);
+    expect(consumed).toBe(false);
+  });
+
+  it('Preview bei move ab 1 CV', () => {
+    const { ctx, previews } = mkCtx();
+    splineTool.handlers.down!(pe(0, 0), ctx);
+    splineTool.handlers.move!(pe(50, 50), ctx);
+    expect(previews.length).toBeGreaterThanOrEqual(1);
+    const last = previews[previews.length - 1];
+    expect(last).not.toBeNull();
+  });
+
+  it('cancel resettet: naechste Sitzung startet frisch', () => {
+    const { ctx, doc } = mkCtx();
+    splineTool.handlers.down!(pe(0, 0), ctx);
+    splineTool.handlers.down!(pe(50, 50), ctx);
+    splineTool.handlers.cancel?.(ctx);
+    splineTool.handlers.down!(pe(0, 0), ctx);
+    splineTool.handlers.down!(pe(50, 50), ctx);
+    splineTool.handlers.down!(pe(100, 0), ctx);
+    splineTool.handlers.key!({ key: 'Enter' } as never, ctx);
+    // 3 CVs der NEUEN Sitzung — controlPoints == 3 (alte 2 nicht gemischt)
+    const el = doc.getAllElements()[0];
+    expect((el.properties.controlPoints as Pt[]).length).toBe(3);
+  });
+
+  it('Status zaehlt CVs mit', () => {
+    const { ctx, statuses } = mkCtx();
+    splineTool.handlers.down!(pe(0, 0), ctx);
+    expect(statuses[0]).toContain('1');
+    expect(statuses[0]).toContain('Spline');
+  });
+
+  it('Manifest: id=spline, ribbonTab=canvas, tags basic', () => {
+    expect(splineTool.manifest.id).toBe('spline');
+    expect(splineTool.manifest.ribbonTab).toBe('canvas');
+    expect((splineTool.manifest.tags ?? [])).toContain('basic');
+  });
+});