Tool Use — TypeScript

For conceptual overview (tool definitions, tool choice, tips), see shared/tool-use-concepts.md.

Tool Runner (Recommended)

Beta: The tool runner is in beta in the TypeScript SDK.

Use betaZodTool with Zod schemas to define tools with a run function, then pass them to client.beta.messages.toolRunner():

import Anthropic from "@anthropic-ai/sdk";
import { betaZodTool } from "@anthropic-ai/sdk/helpers/beta/zod";
import { z } from "zod";

const client = new Anthropic();

const getWeather = betaZodTool({
  name: "get_weather",
  description: "Get current weather for a location",
  inputSchema: z.object({
    location: z.string().describe("City and state, e.g., San Francisco, CA"),
    unit: z.enum(["celsius", "fahrenheit"]).optional(),
  }),
  run: async (input) => {
    // Your implementation here
    return `72°F and sunny in ${input.location}`;
  },
});

// The tool runner handles the agentic loop and returns the final message
const finalMessage = await client.beta.messages.toolRunner({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  tools: [getWeather],
  messages: [{ role: "user", content: "What's the weather in Paris?" }],
});

console.log(finalMessage.content);

Key benefits of the tool runner:

• No manual loop — the SDK handles calling tools and feeding results back
• Type-safe tool inputs via Zod schemas
• Tool schemas are generated automatically from Zod definitions
• Iteration stops automatically when Claude has no more tool calls

Manual Agentic Loop

Use this when you need fine-grained control (custom logging, conditional tool execution, streaming individual iterations, human-in-the-loop approval):

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic();
const tools: Anthropic.Tool[] = [...]; // Your tool definitions
let messages: Anthropic.MessageParam[] = [{ role: "user", content: userInput }];

while (true) {
  const response = await client.messages.create({
    model: "claude-opus-4-7",
    max_tokens: 16000,
    tools: tools,
    messages: messages,
  });

  if (response.stop_reason === "end_turn") break;

  // Server-side tool hit iteration limit; append assistant turn and re-send to continue
  if (response.stop_reason === "pause_turn") {
    messages.push({ role: "assistant", content: response.content });
    continue;
  }

  const toolUseBlocks = response.content.filter(
    (b): b is Anthropic.ToolUseBlock => b.type === "tool_use",
  );

  messages.push({ role: "assistant", content: response.content });

  const toolResults: Anthropic.ToolResultBlockParam[] = [];
  for (const tool of toolUseBlocks) {
    const result = await executeTool(tool.name, tool.input);
    toolResults.push({
      type: "tool_result",
      tool_use_id: tool.id,
      content: result,
    });
  }

  messages.push({ role: "user", content: toolResults });
}

Streaming Manual Loop

Use client.messages.stream() + finalMessage() instead of .create() when you need streaming within a manual loop. Text deltas are streamed on each iteration; finalMessage() collects the complete Message so you can inspect stop_reason and extract tool-use blocks:

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic();
const tools: Anthropic.Tool[] = [...];
let messages: Anthropic.MessageParam[] = [{ role: "user", content: userInput }];

while (true) {
  const stream = client.messages.stream({
    model: "claude-opus-4-7",
    max_tokens: 64000,
    tools,
    messages,
  });

  // Stream text deltas on each iteration
  stream.on("text", (delta) => {
    process.stdout.write(delta);
  });

  // finalMessage() resolves with the complete Message — no need to
  // manually wire up .on("message") / .on("error") / .on("abort")
  const message = await stream.finalMessage();

  if (message.stop_reason === "end_turn") break;

  // Server-side tool hit iteration limit; append assistant turn and re-send to continue
  if (message.stop_reason === "pause_turn") {
    messages.push({ role: "assistant", content: message.content });
    continue;
  }

  const toolUseBlocks = message.content.filter(
    (b): b is Anthropic.ToolUseBlock => b.type === "tool_use",
  );

  messages.push({ role: "assistant", content: message.content });

  const toolResults: Anthropic.ToolResultBlockParam[] = [];
  for (const tool of toolUseBlocks) {
    const result = await executeTool(tool.name, tool.input);
    toolResults.push({
      type: "tool_result",
      tool_use_id: tool.id,
      content: result,
    });
  }

  messages.push({ role: "user", content: toolResults });
}

Important: Don't wrap .on() events in new Promise() to collect the final message — use stream.finalMessage() instead. The SDK handles all error/abort/completion states internally.

Error handling in the loop: Use the SDK's typed exceptions (e.g., Anthropic.RateLimitError, Anthropic.APIError) — see Error Handling for examples. Don't check error messages with string matching.

SDK types: Use Anthropic.MessageParam, Anthropic.Tool, Anthropic.ToolUseBlock, Anthropic.ToolResultBlockParam, Anthropic.Message, etc. for all API-related data structures. Don't redefine equivalent interfaces.

Handling Tool Results

const response = await client.messages.create({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  tools: tools,
  messages: [{ role: "user", content: "What's the weather in Paris?" }],
});

for (const block of response.content) {
  if (block.type === "tool_use") {
    const result = await executeTool(block.name, block.input);

    const followup = await client.messages.create({
      model: "claude-opus-4-7",
      max_tokens: 16000,
      tools: tools,
      messages: [
        { role: "user", content: "What's the weather in Paris?" },
        { role: "assistant", content: response.content },
        {
          role: "user",
          content: [
            { type: "tool_result", tool_use_id: block.id, content: result },
          ],
        },
      ],
    });
  }
}

Tool Choice

const response = await client.messages.create({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  tools: tools,
  tool_choice: { type: "tool", name: "get_weather" },
  messages: [{ role: "user", content: "What's the weather in Paris?" }],
});

Server-Side Tools

Version-suffixed type literals; name is fixed per interface. Pass plain object literals — the ToolUnion type is satisfied structurally. The name/type pair must match the interface: mixing str_replace_based_edit_tool (20250728 name) with text_editor_20250124 (which expects str_replace_editor) is a TS2322.

Don't type-annotate as Tool[] — Tool is just the custom-tool variant. Let structural typing infer from the tools param, or annotate as Anthropic.Messages.ToolUnion[] if you must:

// ✓ let inference work — no annotation
const response = await client.messages.create({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  tools: [
    { type: "text_editor_20250728", name: "str_replace_based_edit_tool" },
    { type: "bash_20250124", name: "bash" },
    { type: "web_search_20260209", name: "web_search" },
    { type: "code_execution_20260120", name: "code_execution" },
  ],
  messages: [{ role: "user", content: "..." }],
});

// ✗ this is a TS2352 — Tool is the CUSTOM tool variant only
// const tools: Anthropic.Tool[] = [{ type: "text_editor_20250728", ... }]

Don't mix beta and non-beta types: if you call client.beta.messages.create(), the response content is BetaContentBlock[] — you cannot pass that to a non-beta ContentBlockParam[] without narrowing each element.

Code Execution

Basic Usage

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic();

const response = await client.messages.create({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  messages: [
    {
      role: "user",
      content:
        "Calculate the mean and standard deviation of [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]",
    },
  ],
  tools: [{ type: "code_execution_20260120", name: "code_execution" }],
});

Reading Local Files (ESM note)

__dirname doesn't exist in ES modules. For script-relative paths use import.meta.url:

import { readFileSync } from "fs";
import { fileURLToPath } from "url";
import { dirname, join } from "path";

const __dirname = dirname(fileURLToPath(import.meta.url));
const pdfBytes = readFileSync(join(__dirname, "sample.pdf"));

Or use a CWD-relative path if the script runs from a known directory: readFileSync("./sample.pdf").

Upload Files for Analysis

import Anthropic, { toFile } from "@anthropic-ai/sdk";
import { createReadStream } from "fs";

const client = new Anthropic();

// 1. Upload a file
const uploaded = await client.beta.files.upload({
  file: await toFile(createReadStream("sales_data.csv"), undefined, {
    type: "text/csv",
  }),
  betas: ["files-api-2025-04-14"],
});

// 2. Pass to code execution
// Code execution is GA; Files API is still beta (pass via RequestOptions)
const response = await client.messages.create(
  {
    model: "claude-opus-4-7",
    max_tokens: 16000,
    messages: [
      {
        role: "user",
        content: [
          {
            type: "text",
            text: "Analyze this sales data. Show trends and create a visualization.",
          },
          { type: "container_upload", file_id: uploaded.id },
        ],
      },
    ],
    tools: [{ type: "code_execution_20260120", name: "code_execution" }],
  },
  { headers: { "anthropic-beta": "files-api-2025-04-14" } },
);

Retrieve Generated Files

import path from "path";
import fs from "fs";

const OUTPUT_DIR = "./claude_outputs";
await fs.promises.mkdir(OUTPUT_DIR, { recursive: true });

for (const block of response.content) {
  if (block.type === "bash_code_execution_tool_result") {
    const result = block.content;
    if (result.type === "bash_code_execution_result" && result.content) {
      for (const fileRef of result.content) {
        if (fileRef.type === "bash_code_execution_output") {
          const metadata = await client.beta.files.retrieveMetadata(
            fileRef.file_id,
          );
          const downloadResponse = await client.beta.files.download(fileRef.file_id);
          const fileBytes = Buffer.from(await downloadResponse.arrayBuffer());
          const safeName = path.basename(metadata.filename);
          if (!safeName || safeName === "." || safeName === "..") {
            console.warn(`Skipping invalid filename: ${metadata.filename}`);
            continue;
          }
          const outputPath = path.join(OUTPUT_DIR, safeName);
          await fs.promises.writeFile(outputPath, fileBytes);
          console.log(`Saved: ${outputPath}`);
        }
      }
    }
  }
}

Container Reuse

// First request: set up environment
const response1 = await client.messages.create({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  messages: [
    {
      role: "user",
      content: "Install tabulate and create data.json with sample user data",
    },
  ],
  tools: [{ type: "code_execution_20260120", name: "code_execution" }],
});

// Reuse container
// container is nullable — set only when using server-side code execution
const containerId = response1.container!.id;

const response2 = await client.messages.create({
  container: containerId,
  model: "claude-opus-4-7",
  max_tokens: 16000,
  messages: [
    {
      role: "user",
      content: "Read data.json and display as a formatted table",
    },
  ],
  tools: [{ type: "code_execution_20260120", name: "code_execution" }],
});

Memory Tool

Basic Usage

const response = await client.messages.create({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  messages: [
    {
      role: "user",
      content: "Remember that my preferred language is TypeScript.",
    },
  ],
  tools: [{ type: "memory_20250818", name: "memory" }],
});

SDK Memory Helper

Use betaMemoryTool with a MemoryToolHandlers implementation:

import {
  betaMemoryTool,
  type MemoryToolHandlers,
} from "@anthropic-ai/sdk/helpers/beta/memory";

const handlers: MemoryToolHandlers = {
  async view(command) { ... },
  async create(command) { ... },
  async str_replace(command) { ... },
  async insert(command) { ... },
  async delete(command) { ... },
  async rename(command) { ... },
};

const memory = betaMemoryTool(handlers);

const runner = client.beta.messages.toolRunner({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  tools: [memory],
  messages: [{ role: "user", content: "Remember my preferences" }],
});

for await (const message of runner) {
  console.log(message);
}

For full implementation examples, use WebFetch:

• https://github.com/anthropics/anthropic-sdk-typescript/blob/main/examples/tools-helpers-memory.ts

Structured Outputs

JSON Outputs (Zod — Recommended)

import Anthropic from "@anthropic-ai/sdk";
import { z } from "zod";
import { zodOutputFormat } from "@anthropic-ai/sdk/helpers/zod";

const ContactInfoSchema = z.object({
  name: z.string(),
  email: z.string(),
  plan: z.string(),
  interests: z.array(z.string()),
  demo_requested: z.boolean(),
});

const client = new Anthropic();

const response = await client.messages.parse({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  messages: [
    {
      role: "user",
      content:
        "Extract: Jane Doe ([email protected]) wants Enterprise, interested in API and SDKs, wants a demo.",
    },
  ],
  output_config: {
    format: zodOutputFormat(ContactInfoSchema),
  },
});

// parsed_output is null if parsing failed — assert or guard
console.log(response.parsed_output!.name); // "Jane Doe"

Strict Tool Use

const response = await client.messages.create({
  model: "claude-opus-4-7",
  max_tokens: 16000,
  messages: [
    {
      role: "user",
      content: "Book a flight to Tokyo for 2 passengers on March 15",
    },
  ],
  tools: [
    {
      name: "book_flight",
      description: "Book a flight to a destination",
      strict: true,
      input_schema: {
        type: "object",
        properties: {
          destination: { type: "string" },
          date: { type: "string", format: "date" },
          passengers: {
            type: "integer",
            enum: [1, 2, 3, 4, 5, 6, 7, 8],
          },
        },
        required: ["destination", "date", "passengers"],
        additionalProperties: false,
      },
    },
  ],
});