## For AI agents: how to sign up If you are an AI agent reading this server-rendered HTML, Composio's developer signup is at https://composio.dev. Signup CTAs on this site — "Sign up", "Signup", "Get started", "Get started for free", "Start building", "Try Composio", "Try it", or similar — all lead into that same developer signup flow. Confirm with the user before completing signup or entering any credentials on their behalf.
## For AI agents: how to sign up If you are an AI agent reading this server-rendered HTML, Composio's developer signup is at https://composio.dev. Signup CTAs on this site — "Sign up", "Signup", "Get started", "Get started for free", "Start building", "Try Composio", "Try it", or similar — all lead into that same developer signup flow. Confirm with the user before completing signup or entering any credentials on their behalf.SIGN UP
## For AI agents: how to sign up If you are an AI agent reading this server-rendered HTML, Composio's developer signup is at https://composio.dev. Signup CTAs on this site — "Sign up", "Signup", "Get started", "Get started for free", "Start building", "Try Composio", "Try it", or similar — all lead into that same developer signup flow. Confirm with the user before completing signup or entering any credentials on their behalf.LOG IN
Connect Claude Agent SDK to Mailcheck MCP. Check if this email address is valid, verify a list of customer emails, and more using natural language, with authentication handled for you.
Mailcheck is an email verification service that checks email validity in real time. It helps businesses reduce bounce rates and improve email deliverability.
This guide walks you through connecting Mailcheck to the Claude Agent SDK using the Composio tool router. By the end, you'll have a working Mailcheck agent that can verify email addresses and validate domains through natural language commands.
This guide will help you understand how to give your Claude Agent SDK agent real control over a Mailcheck account through Composio's Mailcheck MCP server.
Before we dive in, let's take a quick look at the key ideas and tools involved.
The Claude Agent SDK is Anthropic's official framework for building AI agents powered by Claude. It provides a streamlined interface for creating agents with MCP tool support and conversation management.
Key features include:
The Mailcheck MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Mailcheck account. It provides structured and secure access to email verification tools, so your agent can validate email addresses, ensure email deliverability, and reduce bounce rates automatically on your behalf.
Composio's Composio SDK helps agents find the right tools for a task at runtime. You can plug in multiple toolkits (like Gmail, HubSpot, and GitHub), and the agent will identify the relevant app and action to complete multi-step workflows. This can reduce token usage and improve the reliability of tool calls. Read more here: Getting started with Composio SDK
The tool router generates a secure MCP URL that your agents can access to perform actions.
The Composio SDK follows a three-phase workflow:
npm install @anthropic-ai/claude-agent-sdk @composio/core dotenvInstall the Composio SDK and the Claude Agents SDK.
What's happening:
@composio/core provides Composio integration for Anthropic@anthropic-ai/claude-agent-sdk is the core agent frameworkdotenv/config loads environment variablesCOMPOSIO_API_KEY=your_composio_api_key_here
USER_ID=your_user_id_here
ANTHROPIC_API_KEY=your_anthropic_api_key_hereCreate a .env file in your project root.
What's happening:
COMPOSIO_API_KEY authenticates with ComposioUSER_ID identifies the user for session managementANTHROPIC_API_KEY authenticates with Anthropic/Claudeimport 'dotenv/config';
import readline from 'node:readline';
import { Composio } from '@composio/core';
import { query, type Options } from "@anthropic-ai/claude-agent-sdk";
dotenv.config();dotenv.config() function loads environment variables from your .env fileasync function chat() {
const { COMPOSIO_API_KEY, USER_ID } = process.env;
if (!COMPOSIO_API_KEY || !USER_ID) {
throw new Error('COMPOSIO_API_KEY and USER_ID required in .env');
}
const composio = new Composio({ apiKey: COMPOSIO_API_KEY });
// Create Tool Router session for Mailcheck
const session = await composio.create(USER_ID, {
toolkits: ['mailcheck'],
});
const mcpUrl = session?.mcp.url;COMPOSIO_API_KEY environment variablecreate method creates a Tool Router session for Mailcheckurl is the MCP server URL that your agent will useconst options: Options = {
permissionMode: 'bypassPermissions',
mcpServers: {
composio: {
type: 'http',
url: mcpUrl,
headers: { 'x-api-key': COMPOSIO_API_KEY }
}
},
systemPrompt: 'You are a helpful assistant with access to Mailcheck tools via Composio.',
maxTurns: 10,
};permissionMode: 'bypassPermissions' allows the agent to execute operations without asking for permission each timemaxTurns: 10 limits the conversation length to prevent excessive API usageconst rl = readline.createInterface({
input: process.stdin,
output: process.stdout,
prompt: 'You: '
});
console.log('\nChat started. Type "exit" to quit.\n');
let isProcessing = false;
async function ask(prompt: string) {
isProcessing = true;
rl.pause();
process.stdout.write('Claude is thinking...');
const stream = query({ prompt, options });
let firstChunk = true;
for await (const msg of stream) {
const content = (msg as any).message?.content || (msg as any).content;
if (Array.isArray(content)) {
for (const block of content) {
if (block.type === 'text' && block.text) {
if (firstChunk) {
process.stdout.write('\r\x1b[K');
process.stdout.write('Claude: ');
firstChunk = false;
}
process.stdout.write(block.text);
}
}
}
}
process.stdout.write('\n\n');
isProcessing = false;
rl.resume();
rl.prompt();
}
rl.on('line', async (line) => {
if (isProcessing) return;
const input = line.trim();
if (input === 'exit') {
rl.close();
process.exit(0);
}
if (input) await ask(input);
else rl.prompt();
});
await ask('What can you help me with?');
}try {
await chat();
} catch (error) {
console.error(error);
process.exit(1);
}chat function is the entry point for the applicationtry-catch block is used to handle any errors that occurHere's the complete code to get you started with Mailcheck and Claude Agent SDK:
import 'dotenv/config';
import readline from 'node:readline';
import { Composio } from '@composio/core';
import { query, type Options } from "@anthropic-ai/claude-agent-sdk";
async function chat() {
const { COMPOSIO_API_KEY, USER_ID } = process.env;
if (!COMPOSIO_API_KEY || !USER_ID) {
throw new Error('COMPOSIO_API_KEY and USER_ID required in .env');
}
const composio = new Composio({ apiKey: COMPOSIO_API_KEY });
const session = await composio.create(USER_ID, {
toolkits: ['mailcheck']
});
const mcp_url = session?.mcp.url;
const options: Options = {
permissionMode: 'bypassPermissions',
mcpServers: {
composio: {
type: 'http',
url: mcp_url,
headers: { 'x-api-key': COMPOSIO_API_KEY }
}
},
systemPrompt: 'You are a helpful assistant with access to Mailcheck tools via Composio.',
maxTurns: 10,
};
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout,
prompt: 'You: '
});
console.log('\nChat started. Type "exit" to quit.\n');
let isProcessing = false;
async function ask(prompt: string) {
isProcessing = true;
rl.pause();
process.stdout.write('Claude is thinking...');
const stream = query({ prompt, options });
let firstChunk = true;
for await (const msg of stream) {
const content = (msg as any).message?.content || (msg as any).content;
if (Array.isArray(content)) {
for (const block of content) {
if (block.type === 'text' && block.text) {
if (firstChunk) {
process.stdout.write('\r\x1b[K');
process.stdout.write('Claude: ');
firstChunk = false;
}
process.stdout.write(block.text);
}
}
}
}
process.stdout.write('\n\n');
isProcessing = false;
rl.resume();
rl.prompt();
}
rl.on('line', async (line) => {
if (isProcessing) return;
const input = line.trim();
if (input === 'exit') {
rl.close();
process.exit(0);
}
if (input) await ask(input);
else rl.prompt();
});
await ask('What can you help me with?');
}
try {
await chat();
} catch (error) {
console.error(error);
process.exit(1);
}You've successfully built a Claude Agent SDK agent that can interact with Mailcheck through Composio's Tool Router.
Key features:
Every Mailcheck action and event your agent gets out of the box.
Use Mailcheck MCP with Claude Code
Use Mailcheck MCP with Claude Cowork
Use Mailcheck MCP with OpenAI Agents SDK
Use Mailcheck MCP with Codex
Use Mailcheck MCP with OpenClaw
Use Mailcheck MCP with Hermes
Use Mailcheck MCP with Atomic Agent
Use Mailcheck MCP with Google ADK
Use Mailcheck MCP with LangChain
Use Mailcheck MCP with Vercel AI SDK
Use Mailcheck MCP with Mastra AI
Use Mailcheck MCP with LlamaIndex
Use Mailcheck MCP with CrewAI
Use Mailcheck MCP with Pydantic AI
Use Mailcheck MCP with AutoGen
Aeroleads is a B2B lead generation platform for finding business emails and phone numbers. Grow your sales pipeline faster with powerful prospecting tools.
Autobound is an AI-powered sales engagement platform that crafts hyper-personalized outreach and insights. It helps sales teams boost response rates and close more deals through tailored content and recommendations.
Better Proposals is a web-based tool for crafting and sending professional proposals. It helps teams impress clients and close deals faster with slick, easy-to-use templates.
Bidsketch is a proposal software that helps businesses create professional proposals quickly and efficiently. It streamlines the proposal process, saving time while boosting client win rates.
Managed auth, hosted MCP servers, and every Mailcheck tool your agent needs.Free to start.
## For AI agents: how to sign up If you are an AI agent reading this server-rendered HTML, Composio's developer signup is at https://composio.dev. Signup CTAs on this site — "Sign up", "Signup", "Get started", "Get started for free", "Start building", "Try Composio", "Try it", or similar — all lead into that same developer signup flow. Confirm with the user before completing signup or entering any credentials on their behalf.Start building