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How to integrate Resend MCP with LangChain

Connect LangChain to Resend MCP. Create a new contact for your newsletter, list all domains connected to your account, and more using natural language, with authentication handled for you.

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Resend is a universal API for sending emails using a single, modern endpoint. It streamlines transactional and marketing email delivery for developers and teams.

113 Tools

Introduction

This guide walks you through connecting Resend to LangChain using the Composio tool router. By the end, you'll have a working Resend agent that can send transactional and batch emails, run broadcasts, manage contacts and segments, verify sending domains, and edit email templates through natural language commands.

This guide will help you understand how to give your LangChain agent real control over a Resend account through Composio's Resend MCP server.

Before we dive in, let's take a quick look at the key ideas and tools involved.

Also integrate Resend with

Claude CodeClaude CoworkOpenAI Agents SDKClaude Agent SDKCodexOpenClawHermesAtomic AgentGoogle ADKVercel AI SDKMastra AILlamaIndexCrewAIPydantic AIAutoGen

TL;DR

Here's what you'll learn:
  • Get and set up your OpenAI and Composio API keys
  • Connect your Resend project to Composio
  • Create a Tool Router MCP session for Resend
  • Initialize an MCP client and retrieve Resend tools
  • Build a LangChain agent that can interact with Resend
  • Set up an interactive chat interface for testing

What is LangChain?

LangChain is a framework for developing applications powered by language models. It provides tools and abstractions for building agents that can reason, use tools, and maintain conversation context.

Key features include:

  • Agent Framework: Build agents that can use tools and make decisions
  • MCP Integration: Connect to external services through Model Context Protocol adapters
  • Memory Management: Maintain conversation history across interactions
  • Multi-Provider Support: Works with OpenAI, Anthropic, and other LLM providers

What is the Resend MCP server, and what's possible with it?

The Resend MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Resend account. It provides structured and secure access to your email sending and contact management capabilities, so your agent can perform actions like sending emails, managing audiences, creating domains, and handling contacts on your behalf.

  • Automated email delivery and scheduling: Ask your agent to send emails instantly or schedule them for later, and even cancel scheduled messages if needed.
  • Audience and contact management: Let your agent create, list, or delete audiences and individual contacts, keeping your recipient lists organized without manual effort.
  • Domain administration: Easily have your agent set up, list, or remove email sending domains, streamlining onboarding or maintenance for your email infrastructure.
  • Seamless recipient segmentation: Direct your agent to group contacts into audiences for targeted campaigns or communications, improving personalization and reach.
  • Bulk operations and cleanups: Enable your agent to quickly list, update, or delete multiple contacts, audiences, or domains to maintain a tidy and up-to-date email system.

What is the Composio tool router, and how does it fit here?

What is Composio SDK?

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.

How the Composio SDK works

The Composio SDK follows a three-phase workflow:

  1. Discovery: Searches for tools matching your task and returns relevant toolkits with their details.
  2. Authentication: Checks for active connections. If missing, creates an auth config and returns a connection URL via Auth Link.
  3. Execution: Executes the action using the authenticated connection.

Step-by-step Guide

Step by step10 STEPS
1

Prerequisites

Before starting this tutorial, make sure you have:
  • Python 3.10 or higher installed on your system
  • A Composio account with an API key
  • An OpenAI API key
  • Basic familiarity with Python and async programming
2

Getting API Keys for OpenAI and Composio

OpenAI API Key
  • Go to the OpenAI dashboard and create an API key. You'll need credits to use the models, or you can connect to another model provider.
  • Keep the API key safe.
Composio API Key
  • Log in to the Composio dashboard.
  • Navigate to your API settings and generate a new API key.
  • Store this key securely as you'll need it for authentication.
3

Install dependencies

npm install @composio/langchain @langchain/core @langchain/openai @langchain/mcp-adapters dotenv

Install the required packages for LangChain with MCP support.

What's happening:

  • @composio/langchain provides Composio integration for LangChain
  • @langchain/mcp-adapters enables MCP client connections
  • @langchain/core is the core agent framework
  • dotenv/config loads environment variables
4

Set up environment variables

bash
COMPOSIO_API_KEY=your_composio_api_key_here
COMPOSIO_USER_ID=your_composio_user_id_here
OPENAI_API_KEY=your_openai_api_key_here

Create a .env file in your project root.

What's happening:

  • COMPOSIO_API_KEY authenticates your requests to Composio's API
  • COMPOSIO_USER_ID identifies the user for session management
  • OPENAI_API_KEY enables access to OpenAI's language models
5

Import dependencies

import { Composio } from '@composio/core';
import { LangchainProvider } from '@composio/langchain';
import { MultiServerMCPClient } from "@langchain/mcp-adapters";
import { createAgent } from "langchain";
import * as readline from 'readline';
import 'dotenv/config';

dotenv.config();
What's happening:
  • We're importing LangChain's MCP adapter and Composio SDK
  • The dotenv/config import loads environment variables from your .env file
  • This setup prepares the foundation for connecting LangChain with Resend functionality through MCP
6

Initialize Composio client

const composioApiKey = process.env.COMPOSIO_API_KEY;
const userId = process.env.COMPOSIO_USER_ID;

if (!composioApiKey) throw new Error('COMPOSIO_API_KEY is not set');
if (!userId) throw new Error('COMPOSIO_USER_ID is not set');

async function main() {
    const composio = new Composio({
        apiKey: composioApiKey as string,
        provider: new LangchainProvider()
    });
What's happening:
  • We're loading the COMPOSIO_API_KEY from environment variables and validating it exists
  • Creating a Composio instance that will manage our connection to Resend tools
  • Validating that COMPOSIO_USER_ID is also set before proceeding
7

Create a Tool Router session

const session = await composio.create(
    userId as string,
    {
        toolkits: ['resend']
    }
);

const url = session.mcp.url;
What's happening:
  • We're creating a Tool Router session that gives your agent access to Resend tools
  • The create method takes the user ID and specifies which toolkits should be available
  • The returned session.mcp.url is the MCP server URL that your agent will use
  • This approach allows the agent to dynamically load and use Resend tools as needed
8

Configure the agent with the MCP URL

const client = new MultiServerMCPClient({
    "resend-agent": {
        transport: "http",
        url: url,
        headers: {
            "x-api-key": process.env.COMPOSIO_API_KEY
        }
    }
});

const tools = await client.getTools();

const agent = createAgent({ model: "gpt-5", tools });
What's happening:
  • We're creating a MultiServerMCPClient that connects to our Resend MCP server via HTTP
  • The client is configured with a name and the URL from our Tool Router session
  • getTools() retrieves all available Resend tools that the agent can use
  • We're creating a LangChain agent using the GPT-5 model
9

Set up interactive chat interface

let conversationHistory: any[] = [];

console.log("Chat started! Type 'exit' or 'quit' to end the conversation.\n");
console.log("Ask any Resend related question or task to the agent.\n");

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
    prompt: 'You: '
});

rl.prompt();

rl.on('line', async (userInput: string) => {
    const trimmedInput = userInput.trim();

    if (['exit', 'quit', 'bye'].includes(trimmedInput.toLowerCase())) {
        console.log("\nGoodbye!");
        rl.close();
        process.exit(0);
    }

    if (!trimmedInput) {
        rl.prompt();
        return;
    }

    conversationHistory.push({ role: "user", content: trimmedInput });
    console.log("\nAgent is thinking...\n");

    const response = await agent.invoke({ messages: conversationHistory });
    conversationHistory = response.messages;

    const finalResponse = response.messages[response.messages.length - 1]?.content;
    console.log(`Agent: ${finalResponse}\n`);
        
        rl.prompt();
    });

    rl.on('close', () => {
        console.log('\n👋 Session ended.');
        process.exit(0);
    });
What's happening:
  • We initialize an empty conversationHistory list to maintain context across interactions
  • A readline interface is used to continuously accept user input from the command line
  • When a user types a message, it's added to the conversation history and sent to the agent
  • The agent processes the request using the invoke() method with the full conversation history
  • Users can type 'exit', 'quit', or 'bye' to end the chat session gracefully
10

Run the application

main().catch((err) => {
    console.error('Fatal error:', err);
    process.exit(1);
});
What's happening:
  • We call the main() function to start the application

Complete Code

Here's the complete code to get you started with Resend and LangChain:

import { Composio } from '@composio/core';
import { LangchainProvider } from '@composio/langchain';
import { MultiServerMCPClient } from "@langchain/mcp-adapters";  
import { createAgent } from "langchain";
import * as readline from 'readline';
import 'dotenv/config';

const composioApiKey = process.env.COMPOSIO_API_KEY;
const userId = process.env.COMPOSIO_USER_ID;

if (!composioApiKey) throw new Error('COMPOSIO_API_KEY is not set');
if (!userId) throw new Error('COMPOSIO_USER_ID is not set');

async function main() {
    const composio = new Composio({
        apiKey: composioApiKey as string,
        provider: new LangchainProvider()
    });

    const session = await composio.create(
        userId as string,
        {
            toolkits: ['resend']
        }
    );

    const url = session.mcp.url;
    
    const client = new MultiServerMCPClient({
        "resend-agent": {
            transport: "http",
            url: url,
            headers: {
                "x-api-key": process.env.COMPOSIO_API_KEY
            }
        }
    });
    
    const tools = await client.getTools();
  
    const agent = createAgent({ model: "gpt-5", tools });
    
    let conversationHistory: any[] = [];
    
    console.log("Chat started! Type 'exit' or 'quit' to end the conversation.\n");
    console.log("Ask any Resend related question or task to the agent.\n");
    
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout,
        prompt: 'You: '
    });

    rl.prompt();

    rl.on('line', async (userInput: string) => {
        const trimmedInput = userInput.trim();
        
        if (['exit', 'quit', 'bye'].includes(trimmedInput.toLowerCase())) {
            console.log("\nGoodbye!");
            rl.close();
            process.exit(0);
        }
        
        if (!trimmedInput) {
            rl.prompt();
            return;
        }
        
        conversationHistory.push({ role: "user", content: trimmedInput });
        console.log("\nAgent is thinking...\n");
        
        const response = await agent.invoke({ messages: conversationHistory });
        conversationHistory = response.messages;
        
        const finalResponse = response.messages[response.messages.length - 1]?.content;
        console.log(`Agent: ${finalResponse}\n`);
        
        rl.prompt();
    });

    rl.on('close', () => {
        console.log('\nSession ended.');
        process.exit(0);
    });
}

main().catch((err) => {
    console.error('Fatal error:', err);
    process.exit(1);
});

Conclusion

You've successfully built a LangChain agent that can interact with Resend through Composio's Tool Router.

Key features of this implementation:

  • Dynamic tool loading through Composio's Tool Router
  • Conversation history maintenance for context-aware responses
  • Async Python provides clean, efficient execution of agent workflows
You can extend this further by adding error handling, implementing specific business logic, or integrating additional Composio toolkits to create multi-app workflows.
TOOLS

Supported Tools

Every Resend action and event your agent gets out of the box.

Add Contact To Segment

Add an existing contact to a segment in Resend.

Batch Add Suppressions

Add between 1 and 100 Resend suppressions to prevent sending to those emails.

Batch Remove Suppressions

Remove 1–100 Resend suppressions by email addresses or suppression IDs, but not both.

Cancel Broadcast

Cancel a queued or scheduled broadcast.

Cancel Email

Cancel a scheduled email.

Create API Key

Create a new API key to authenticate communications with Resend.

Create Audience

Create a segment using the legacy audience action and response shape.

Create Automation

Create a Resend automation from workflow steps and connections.

Create Contact

Create a global contact and add it to the segment identified by audienceId.

Create Contact Import

Create a contact import from a CSV file, optionally mapping columns and applying segments and topic subscriptions.

Create Contact Property

Tool to create a new contact property in Resend.

Create Contact V2

Tool to create a new contact in Resend.

Create Domain

Create a domain through the Resend Email API.

Create Domain Claim

Start a claim for a domain another Resend account has already verified.

Create Draft Broadcast

Create a broadcast and leave it as an unsent draft.

Create Event

Create a Resend event definition, optionally with a typed payload schema.

Create Segment

Create a new segment for contacts to be added to.

Create Suppression

Create a Resend suppression for an email address to prevent sending to it.

Create Template

Tool to create a new email template in Resend.

Create Topic

Tool to create a new topic to segment your audience.

Create Webhook

Tool to create a webhook to receive real-time notifications about email events.

Delete API Key

Remove an existing API key from Resend.

Delete Audience

Remove a segment using the legacy audience action and response shape.

Delete Automation

Remove an existing automation from Resend using its automation ID.

Delete Broadcast

Remove an existing broadcast that is in draft status.

Delete Contact

Remove a contact from the segment identified by audienceId, preserving the global contact.

Delete Contact By ID

Tool to remove an existing contact by its ID.

Delete Contact Property

Remove an existing contact property from Resend.

Delete Domain

Delete a domain through the Resend Email API.

Delete Event

Delete an existing Resend event using its event ID (UUID) or event name.

Delete Segment

Remove an existing segment.

Delete Suppression

Remove a Resend suppression using its suppression ID or email address.

Delete Template

Remove an existing template.

Delete Topic

Delete an existing Resend topic by its topic ID.

Delete Webhook

Remove an existing webhook by ID.

Duplicate Automation

Duplicate an existing automation by its ID and return the new automation's ID.

Duplicate Broadcast

Create a new draft broadcast from an existing broadcast.

Duplicate Template

Duplicate an existing template through the Resend Email API.

Get Automation

Retrieve a Resend automation by ID, including its active workflow steps and connections.

Get Automation Run

Retrieve a Resend automation run by automation and run IDs, including its status and step executions in graph order.

Get Broadcast

Retrieve a single broadcast by its ID.

Get Contact

Tool to retrieve a single contact from Resend by ID or email.

Get Contact Import

Retrieve a contact import by ID to check its status, timestamps, and processed row counts.

Get Contact Property

Tool to retrieve a single contact property from Resend.

Get Domain Claim

Retrieve the latest claim for a placeholder domain created by a claim.

Get Email Attachment

Retrieve a single attachment from a sent email.

Get Email Metrics

Retrieve account-level email metrics over a date range, with optional filters and dimension breakdowns.

Get Event

Retrieve a Resend event definition by UUID or event name.

Get Log

Retrieve a single Resend API log by its ID.

Get Received Email

Retrieve a single received email by ID, including its content, headers, recipients, and attachment metadata.

Get Received Email Attachment

Retrieve a single attachment from a received email, including its metadata and signed download URL.

Get Segment

Retrieve a single segment by its ID.

Get Suppression

Retrieve a Resend suppression by ID or email address.

Get Template

Retrieve a single template by ID or alias from Resend.

Get Topic

Tool to retrieve a single topic by its ID in Resend.

Get Usage

Retrieve the account's current usage and plan limits for emails, contacts, segments, broadcasts, AI credits, automation runs, domains, and API requests.

Get Webhook

Retrieve a single webhook for the authenticated user.

Get Webhook Event

Retrieve a single webhook event by webhook ID and event ID.

List All Contacts

Tool to retrieve a list of all contacts from Resend.

List API Keys

Tool to retrieve a list of API keys for the authenticated user.

List Audiences

List segments using the legacy audience action and response shape.

List Automation Runs

Retrieve a page of runs for a Resend automation.

List Automations

Retrieve a page of Resend automations.

List Broadcast Clicked Links

Retrieve one page of a broadcast's clicked URLs and total and unique click counts.

List Broadcast Recipients

Retrieve a page of broadcast recipients filtered by a required event type.

List Broadcasts

Tool to retrieve a list of broadcasts.

List Contact Imports

Retrieve a page of Resend contact imports, optionally filtered by status.

List Contact Properties

Tool to retrieve a list of contact properties from Resend.

List Contacts

List contacts belonging to the segment identified by the legacy audienceId parameter.

List Contact Segments

Retrieve a list of segments that a contact is part of.

List Contact Topics

Retrieve a list of topic subscriptions for a contact in Resend.

List Domains

List all domains.

List Email Attachments

Tool to retrieve a list of attachments from a sent email.

List Emails

Tool to retrieve a list of emails sent by your team.

List Events

Retrieve a page of Resend event definitions and their payload schemas.

List Logs

Retrieve a page of Resend API request logs with optional cursor pagination.

List Received Email Attachments

Retrieve a paginated list of attachments for a received email, including metadata and signed download URLs.

List Received Emails

Tool to retrieve a list of received emails for the authenticated user.

List Segments

Retrieve a page of Resend segments for audience management.

List Suppressions

Retrieve a page of suppressed email addresses from Resend, optionally filtered by bounce, complaint, or manual origin.

List Templates

Tool to retrieve a list of templates from Resend.

List Topics

Tool to retrieve a list of topics for the authenticated user.

List Webhook Event Attempts

Retrieve a page of delivery attempts for an event on a Resend webhook, including HTTP status codes, response bodies, and send timestamps.

List Webhook Events

Retrieve a page of events for a Resend webhook, including delivery status.

List Webhooks

Retrieve a list of webhooks for the authenticated user.

Publish Template

Publish a template through the Resend Email API.

Remove Contact From Segment

Remove an existing contact from a segment.

Replay Webhook Event

Queue one more delivery of an event to an enabled webhook.

Retrieve Audience

Retrieve a segment using the legacy audience action and response shape.

Retrieve Contact

Retrieve a global contact by ID.

Retrieve Domain

Retrieve a single domain.

Retrieve Email

Retrieve a single email.

Send Batch Emails

Trigger up to 100 batch emails at once.

Send Broadcast

Send an existing Resend broadcast immediately or schedule it for a later ISO 8601 date.

Send Email

Send an email using Resend.

Send Event

Send an event associated with a contact ID or email, with an optional payload.

Share Email

Create a shareable link for a sent or received Resend email.

Stop Automation

Stop an automation by its ID and return its status after stopping.

Update Automation

Update a Resend automation's name, status, or workflow graph.

Update Broadcast

Update an existing broadcast in Resend.

Update Contact

Tool to update an existing contact in Resend by ID or email.

Update Contact Property

Update an existing contact property in Resend.

Update Contact Topics

Update topic subscriptions for a Resend contact by ID or email address.

Update Domain

Update an existing domain's click tracking, open tracking, and TLS settings.

Update Draft Broadcast

Update a broadcast that is still an unsent draft.

Update Email

Update the scheduled send time of a scheduled email by ID.

Update Event

Update a Resend event definition's payload schema by UUID or event name.

Update Segment

Update an existing segment in Resend.

Update Template

Tool to update an existing email template in Resend.

Update Topic

Tool to update an existing topic in Resend.

Update Webhook

Tool to update an existing webhook configuration.

Verify Domain

Verify a domain through the Resend Email API.

Verify Domain Claim

Trigger asynchronous DNS verification and ownership transfer for a domain claim.

FRAMEWORKS

How to build Resend MCP Agent with another framework

Claude Code logo

Claude Code

Use Resend MCP with Claude Code

Claude Cowork logo

Claude Cowork

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OpenAI Agents SDK logo

OpenAI Agents SDK

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Claude Agent SDK logo

Claude Agent SDK

Use Resend MCP with Claude Agent SDK

Codex logo

Codex

Use Resend MCP with Codex

OpenClaw logo

OpenClaw

Use Resend MCP with OpenClaw

Hermes logo

Hermes

Use Resend MCP with Hermes

Atomic Agent logo

Atomic Agent

Use Resend MCP with Atomic Agent

Google ADK logo

Google ADK

Use Resend MCP with Google ADK

Vercel AI SDK logo

Vercel AI SDK

Use Resend MCP with Vercel AI SDK

Mastra AI logo

Mastra AI

Use Resend MCP with Mastra AI

LlamaIndex logo

LlamaIndex

Use Resend MCP with LlamaIndex

CrewAI logo

CrewAI

Use Resend MCP with CrewAI

Pydantic AI logo

Pydantic AI

Use Resend MCP with Pydantic AI

AutoGen logo

AutoGen

Use Resend MCP with AutoGen

FAQ

Frequently asked questions

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