Tool Bridging

Built-in tools

SDK inherits the CLI’s built-in tool catalog: Read, Write, Edit, Bash, Glob, Grep, WebSearch, WebFetch, AskUserQuestion, Monitor, Agent (for subagents), and others. See Tools/README.md for full reference.

Custom tools via MCP

SDK can instantiate MCP servers in-process (via tool() and createSdkMcpServer() functions) or connect to external stdio/HTTP/SSE servers.

import { tool, createSdkMcpServer } from "@anthropic-ai/claude-agent-sdk";
import { z } from "zod";

const greet = tool(
  "greet",
  "Greet a user",
  { name: z.string() },
  async ({ name }) => ({ content: [{ type: "text", text: `Hello, ${name}!` }] })
);

const server = createSdkMcpServer({
  name: "greeting",
  tools: [greet]
});

// Use with query()
for await (const msg of query({
  prompt: "Greet Alice",
  options: {
    mcpServers: { greeting: server },
    allowedTools: ["mcp__greeting__greet"]
  }
})) { }

canUseTool callback (SDK-specific)

Fires before each tool dispatch. Replaces or augments settings.json permission rules at runtime.

canUseTool: async (toolName, input, context) => {
  if (toolName === "Bash" && input.command?.includes("rm")) {
    return { behavior: "deny", message: "Destructive commands blocked" };
  }
  return { behavior: "allow" };
}

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