diff --git a/src/models/anthropic.test.ts b/src/models/anthropic.test.ts
index d4fb0b6..2f2a288 100644
--- a/src/models/anthropic.test.ts
+++ b/src/models/anthropic.test.ts
@@ -1,25 +1,29 @@
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 import { AnthropicClient } from './anthropic.js';
 
-// Mock the SDK
+// Shared mock function so we can override per-test
+const mockCreate = vi.fn().mockResolvedValue({
+  content: [{ type: 'text', text: 'Hello from Claude!' }],
+  stop_reason: 'end_turn',
+  usage: { input_tokens: 10, output_tokens: 5 },
+});
+
+const mockStream = vi.fn().mockReturnValue({
+  [Symbol.asyncIterator]: async function* () {
+    yield { type: 'content_block_delta', delta: { type: 'text_delta', text: 'Hello ' } };
+    yield { type: 'content_block_delta', delta: { type: 'text_delta', text: 'from ' } };
+    yield { type: 'content_block_delta', delta: { type: 'text_delta', text: 'Claude!' } };
+  },
+  finalMessage: vi.fn().mockResolvedValue({
+    usage: { input_tokens: 10, output_tokens: 5 },
+  }),
+});
+
 vi.mock('@anthropic-ai/sdk', () => ({
   default: vi.fn().mockImplementation(() => ({
     messages: {
-      create: vi.fn().mockResolvedValue({
-        content: [{ type: 'text', text: 'Hello from Claude!' }],
-        stop_reason: 'end_turn',
-        usage: { input_tokens: 10, output_tokens: 5 },
-      }),
-      stream: vi.fn().mockReturnValue({
-        [Symbol.asyncIterator]: async function* () {
-          yield { type: 'content_block_delta', delta: { type: 'text_delta', text: 'Hello ' } };
-          yield { type: 'content_block_delta', delta: { type: 'text_delta', text: 'from ' } };
-          yield { type: 'content_block_delta', delta: { type: 'text_delta', text: 'Claude!' } };
-        },
-        finalMessage: vi.fn().mockResolvedValue({
-          usage: { input_tokens: 10, output_tokens: 5 },
-        }),
-      }),
+      create: mockCreate,
+      stream: mockStream,
     },
   })),
 }));
@@ -68,3 +72,37 @@ describe('AnthropicClient streaming', () => {
     expect(finalUsage).toEqual({ inputTokens: 10, outputTokens: 5 });
   });
 });
+
+describe('AnthropicClient tool use', () => {
+  it('passes tools to API and parses tool_use response', async () => {
+    mockCreate.mockResolvedValueOnce({
+      content: [
+        { type: 'tool_use', id: 'toolu_01', name: 'shell.exec', input: { command: 'ls' } },
+      ],
+      stop_reason: 'tool_use',
+      usage: { input_tokens: 20, output_tokens: 15 },
+    });
+
+    const client = new AnthropicClient({
+      apiKey: 'test-key',
+      model: 'claude-sonnet-4-20250514',
+    });
+
+    const response = await client.chat({
+      messages: [{ role: 'user', content: 'list files' }],
+      tools: [{
+        name: 'shell.exec',
+        description: 'Run shell command',
+        input_schema: { type: 'object', properties: { command: { type: 'string' } }, required: ['command'] },
+      }],
+    });
+
+    expect(response.stopReason).toBe('tool_use');
+    expect(response.toolCalls).toHaveLength(1);
+    expect(response.toolCalls![0]).toEqual({
+      id: 'toolu_01',
+      name: 'shell.exec',
+      args: { command: 'ls' },
+    });
+  });
+});
diff --git a/src/models/anthropic.ts b/src/models/anthropic.ts
index 5cf624d..a92bc86 100644
--- a/src/models/anthropic.ts
+++ b/src/models/anthropic.ts
@@ -1,4 +1,5 @@
 import Anthropic from '@anthropic-ai/sdk';
+import type { Message } from '@anthropic-ai/sdk/resources/messages/messages.js';
 import type { ChatRequest, ChatResponse, ChatStreamEvent, ModelClient } from './types.js';
 
 export interface AnthropicClientConfig {
@@ -23,7 +24,7 @@ export class AnthropicClient implements ModelClient {
   }
 
   async chat(request: ChatRequest): Promise<ChatResponse> {
-    const response = await this.client.messages.create({
+    const params: Record<string, unknown> = {
       model: this.model,
       max_tokens: request.maxTokens ?? this.defaultMaxTokens,
       system: request.system,
@@ -31,11 +32,21 @@ export class AnthropicClient implements ModelClient {
         role: m.role,
         content: m.content,
       })),
-    });
+    };
+
+    if (request.tools && request.tools.length > 0) {
+      params.tools = request.tools;
+    }
+
+    const response = await this.client.messages.create(params as unknown as Parameters<typeof this.client.messages.create>[0]) as Message;
 
     const textContent = response.content.find((c) => c.type === 'text');
     const content = textContent?.type === 'text' ? textContent.text : '';
 
+    const toolCalls = response.content
+      .filter((c): c is { type: 'tool_use'; id: string; name: string; input: unknown } => c.type === 'tool_use')
+      .map(c => ({ id: c.id, name: c.name, args: c.input }));
+
     return {
       content,
       stopReason: response.stop_reason ?? 'end_turn',
@@ -43,6 +54,7 @@ export class AnthropicClient implements ModelClient {
         inputTokens: response.usage.input_tokens,
         outputTokens: response.usage.output_tokens,
       },
+      ...(toolCalls.length > 0 ? { toolCalls } : {}),
     };
   }