How to integrate Postgrid MCP with LangChain

This guide walks you through connecting Postgrid to LangChain using the Composio tool router. By the end, you'll have a working Postgrid agent that can send a letter to new customer address, verify and standardize a shipping address, create a reusable postcard template through natural language commands. This guide will help you understand how to give your LangChain agent real control over a Postgrid account through Composio's Postgrid MCP server. Before we dive in, let's take a quick look at the key ideas and tools involved.

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Postgrid

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Postgrid is an API platform for automating direct mail and address verification. It helps businesses send mail and verify addresses instantly, reducing manual effort and errors.

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Introduction

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

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

Also integrate Postgrid with

OpenAI Agents SDK Claude Agent SDK Claude Code Claude Cowork Codex OpenClaw Hermes CLI Google ADK Vercel AI SDK Mastra AI LlamaIndex CrewAI

TL;DR

Here's what you'll learn:

Get and set up your OpenAI and Composio API keys
Connect your Postgrid project to Composio
Create a Tool Router MCP session for Postgrid
Initialize an MCP client and retrieve Postgrid tools
Build a LangChain agent that can interact with Postgrid
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 Postgrid MCP server, and what's possible with it?

The Postgrid MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Postgrid account. It provides structured and secure access to your direct mail and address automation tools, so your agent can verify addresses, send letters, manage contacts, and handle templates for your business communications—all without manual intervention.

Automated letter sending: Have your agent create and send physical letters on demand, handling recipient, sender, and content details seamlessly.
Contact management: Effortlessly add, update, or delete contacts in your Postgrid account to keep your mailing lists accurate and up to date.
Template creation and maintenance: Let your agent generate reusable mail templates with dynamic placeholders, and remove outdated templates as needed.
Bank account and payment management: Create or delete bank accounts associated with print and mail services, ensuring smooth financial operations for mail automation.
Webhook setup and monitoring: Enable your agent to create or remove webhooks to track events and receive real-time notifications for your mail orders and services.

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:

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

Step-by-step Guide

Step by step10 STEPS

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

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.

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

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

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 Postgrid functionality through MCP

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 Postgrid tools
Validating that COMPOSIO_USER_ID is also set before proceeding

Create a Tool Router session

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

const url = session.mcp.url;

What's happening:

We're creating a Tool Router session that gives your agent access to Postgrid 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 Postgrid tools as needed

Configure the agent with the MCP URL

const client = new MultiServerMCPClient({
    "postgrid-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 Postgrid MCP server via HTTP
The client is configured with a name and the URL from our Tool Router session
getTools() retrieves all available Postgrid tools that the agent can use
We're creating a LangChain agent using the GPT-5 model

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 Postgrid 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

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 Postgrid 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: ['postgrid']
        }
    );

    const url = session.mcp.url;
    
    const client = new MultiServerMCPClient({
        "postgrid-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 Postgrid 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 Postgrid 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 Postgrid action and event your agent gets out of the box.

Cancel Box

Tool to cancel a box order by its ID.

Cancel Cheque

Tool to cancel a cheque order by its ID.

Cancel Cheque with Note

Tool to cancel a cheque order with a cancellation note.

Cancel Postcard

Tool to cancel a postcard order.

Cancel Postcard With Note

Tool to cancel a postcard order with an optional cancellation note.

Cancel Return Envelope Order

Tool to cancel a return envelope order.

CREATE_BANK_ACCOUNT

Tool to create a new bank account for print & mail service.

Create Box

Tool to create a box mailing order for letters with plastic cards or cheques.

Create Cheque

Tool to create a cheque order for physical cheque mailing.

Create Contact

Tool to create a new contact in PostGrid.

Create Letter

Tool to create and send a letter via PostGrid.

Create Postcard

Tool to create and send a postcard via PostGrid.

Create Return Envelope

Tool to create a return envelope for mail recipients to respond.

Create Return Envelope Order

Tool to create a batch order of return envelopes to be printed and delivered.

Create Template

Tool to create a new mail template in PostGrid.

Create Template Editor Session

Tool to create a template editor session for interactive template editing.

Create Tracker

Tool to create a tracker for monitoring mail delivery status via URL tracking.

Create Webhook

Tool to create a new webhook to receive order event notifications.

Delete Bank Account

Tool to delete a bank account by its ID.

Delete Contact

Tool to delete a contact by its ID.

Delete Template

Tool to delete a template by its ID.

Delete Template Editor Session

Tool to delete a template editor session by its ID.

Delete Tracker

Tool to delete a tracker by its ID.

Delete Webhook

Tool to delete a webhook subscription.

Fill Test Return Envelope Order

Tool to fill a test return envelope order for testing purposes.

Get Bank Account

Tool to retrieve a bank account.

Get Box

Tool to retrieve a specific box order by ID.

Get Cheque

Tool to retrieve a specific cheque by ID.

Get Contact

Tool to retrieve a contact.

Get Letter

Tool to retrieve a letter.

Get Postcard

Tool to retrieve a specific postcard by ID.

Get Return Envelope

Tool to retrieve a return envelope.

Get Return Envelope Order

Tool to retrieve a specific return envelope order.

Get Template

Tool to retrieve a template.

Get Tracker

Tool to retrieve a tracker.

Get Webhook

Tool to retrieve details of a specific webhook by its ID.

List Bank Accounts

Tool to list bank accounts.

List Box Orders

Tool to list box orders.

List Cheques

Tool to list cheques with optional filters and pagination.

List Contacts

Tool to list contacts.

List Webhook Events

Tool to retrieve a list of webhook events with optional pagination.

List Letters

Tool to list letters.

List Postal Statements

Tool to list all postal statements for billing and tracking purposes.

List Postcards

Tool to retrieve a list of postcards with optional filtering and pagination.

List Return Envelope Orders

Tool to list all return envelope orders for a specific return envelope.

List Return Envelopes

Tool to list return envelopes.

List Self-Mailers

Tool to list self-mailers.

List Sub-Organizations

Tool to list sub-organizations.

List Template Editor Sessions

Tool to list template editor sessions.

List Templates

Tool to list templates.

List Trackers

Tool to list all trackers.

List Tracker Visits

Tool to list all visits for a tracker.

List Webhook Invocations

Tool to list previous invocations of a webhook with response status codes.

List Webhooks

Tool to retrieve a list of configured webhooks with optional filtering and pagination.

Progress Test Box

Tool to progress a test box through processing stages for webhook testing.

Progress Test Cheque

Tool to progress a test cheque through processing stages for webhook testing.

Progress Test Postcard

Tool to progress a test postcard through processing stages for webhook testing.

Update Template

Tool to update an existing mail template in PostGrid.

Update Tracker

Tool to update an existing tracker's redirect URL template and/or expiration settings.

Update Webhook

Tool to update an existing webhook configuration.

FRAMEWORKS

How to build Postgrid MCP Agent with another framework

OpenAI Agents SDK

Use Postgrid MCP with OpenAI Agents SDK

Claude Agent SDK

Use Postgrid MCP with Claude Agent SDK

Claude Code

Use Postgrid MCP with Claude Code

Claude Cowork

Use Postgrid MCP with Claude Cowork

Codex

Use Postgrid MCP with Codex

OpenClaw

Use Postgrid MCP with OpenClaw

Hermes

Use Postgrid MCP with Hermes

CLI

Use Postgrid MCP with CLI

Google ADK

Use Postgrid MCP with Google ADK

Vercel AI SDK

Use Postgrid MCP with Vercel AI SDK

Mastra AI

Use Postgrid MCP with Mastra AI

LlamaIndex

Use Postgrid MCP with LlamaIndex

CrewAI

Use Postgrid MCP with CrewAI

MORE TOOLKITS

Explore Other Toolkits

Toolkit marketplace

Gmail

Oauth2

Gmail is Google's email service with powerful spam protection, search, and G Suite integration. It keeps your inbox organized and makes communication fast and reliable.

Google Calendar

Oauth2

Google Calendar is a time management service for scheduling meetings, events, and reminders. It streamlines personal and team organization with integrated notifications and sharing options.

Google Drive

Oauth2

Google Drive is a cloud storage platform for uploading, sharing, and collaborating on files. It's perfect for keeping your documents accessible and organized across devices.

Outlook

Oauth2S2s Oauth2

Outlook is Microsoft's email and calendaring platform for unified communications and scheduling. It helps users stay organized with powerful email, contacts, and calendar management.

FAQ

Frequently asked questions

With a standalone Postgrid MCP server, the agents and LLMs can only access a fixed set of Postgrid tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from Postgrid and many other apps based on the task at hand, all through a single MCP endpoint.

Yes, you can. LangChain fully supports MCP integration. You get structured tool calling, message history handling, and model orchestration while Tool Router takes care of discovering and serving the right Postgrid tools.

Yes, absolutely. You can configure which Postgrid scopes and actions are allowed when connecting your account to Composio. You can also bring your own OAuth credentials or API configuration so you keep full control over what the agent can do.

All sensitive data such as tokens, keys, and configuration is fully encrypted at rest and in transit. Composio is SOC 2 Type 2 compliant and follows strict security practices so your Postgrid data and credentials are handled as safely as possible.

Start with Postgrid.It takes 30 seconds.

Managed auth, hosted MCP servers, and every Postgrid tool your agent needs.Free to start.

Start building

Customer stories

Teams ship real agents on Composio

GET STARTED FOR FREE BOOK A DEMO

Karan skipped his own birthday party to fix our critical issue. It was 10pm and he diverted his Waymo to help us instead. This really sets the bar — it shows the commitment you need when users rely on your software.

Harsha Gaddipati

Co-founder, Slashy

A lot of students tell us that the moment their connected tools start talking to each other inside Opennote feels almost magical. The agent just knows them, and it's immensely helped keep new users on the platform.

Abhi Arya

Co-founder, Opennote

We chose Composio over Pipedream because it delivered depth where it mattered — niche tools and tricky edge cases other platforms simply ignored. That gave us confidence to scale without compromising.

Nirman Dave

CEO, Zams

As a solo builder, shipping fast is life or death. The only way I can outcompete incumbents is by outmanoeuvring them. Getting bogged down managing agent auth would have been a death sentence.

Ryan Yu

Founder, Extra Thursday

Before Composio, adding tool integrations was slow and resource-intensive. Each one could take weeks of engineering time, and maintaining them meant constantly keeping up with API changes.

Tomisin Jenrola

Founder & CEO, SwarmZero

With hands-on help from their founder, we integrated Gmail and Google Drive in just 30 minutes. This level of personal support and commitment is exactly what startups should strive for.

Jerome Leclanche

Co-Founder, Ingram Technologies

How to integrate Postgrid MCP with LangChain

Connect Postgrid without auth hassles

Introduction

Also integrate Postgrid with

TL;DR

What is LangChain?

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

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

What is Composio SDK?

How the Composio SDK works

Step-by-step Guide

Prerequisites

Getting API Keys for OpenAI and Composio

Install dependencies

Set up environment variables

Import dependencies

Initialize Composio client

Create a Tool Router session

Configure the agent with the MCP URL

Set up interactive chat interface

Run the application

Complete Code

Conclusion

Supported Tools

How to build Postgrid MCP Agent with another framework

OpenAI Agents SDK

Claude Agent SDK

Claude Code

Claude Cowork

Codex

OpenClaw

Hermes

CLI

Google ADK

Vercel AI SDK

Mastra AI

LlamaIndex

CrewAI

Explore Other Toolkits

Gmail

Google Calendar

Google Drive

Outlook

Frequently asked questions

What are the differences in Tool Router MCP and Postgrid MCP?+

Can I use Tool Router MCP with LangChain?+

Can I manage the permissions and scopes for Postgrid while using Tool Router?+

How safe is my data with Composio Tool Router?+

Start with Postgrid.It takes 30 seconds.

Teams ship real agents on Composio