How to integrate Blocknative MCP with LangChain

This guide walks you through connecting Blocknative to LangChain using the Composio tool router. By the end, you'll have a working Blocknative agent that can monitor transaction status for a given hash, fetch current ethereum gas price distribution, list all supported blockchains for monitoring through natural language commands. This guide will help you understand how to give your LangChain agent real control over a Blocknative account through Composio's Blocknative MCP server. Before we dive in, let's take a quick look at the key ideas and tools involved.

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Introduction

This guide walks you through connecting Blocknative to LangChain using the Composio tool router. By the end, you'll have a working Blocknative agent that can monitor transaction status for a given hash, fetch current ethereum gas price distribution, list all supported blockchains for monitoring through natural language commands.

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

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

Also integrate Blocknative with

OpenAI Agents SDKClaude Agent SDKClaude CodeClaude CoworkCodexOpenClawHermesCLIGoogle ADKVercel AI SDKMastra AILlamaIndexCrewAI

TL;DR

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

The Blocknative MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Blocknative account. It provides structured and secure access to real-time mempool data and transaction management features across public blockchains, so your agent can monitor transactions, analyze gas prices, configure filters, and manage blockchain event subscriptions on your behalf.

  • Real-time mempool monitoring: Instruct your agent to subscribe to Ethereum transaction hashes or addresses and receive instant updates on their status and events.
  • Gas price analysis and estimation: Have your agent fetch current gas price distributions, base fee predictions, and inclusion probability estimates to help optimize transaction fees.
  • Customizable event filters: Let your agent configure advanced mempool filters and ABI decoding, so you can track only the events or transactions that matter to your workflow.
  • Multichain event subscriptions: Enable your agent to subscribe or unsubscribe to transaction and account events across multiple supported blockchains using the Blocknative multichain SDK.
  • Supported chain discovery: Ask your agent to list and discover which blockchains and gas oracles are available for monitoring and analytics.

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 Blocknative 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 Blocknative 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: ['blocknative']
    }
);

const url = session.mcp.url;
What's happening:
  • We're creating a Tool Router session that gives your agent access to Blocknative 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 Blocknative tools as needed
8

Configure the agent with the MCP URL

const client = new MultiServerMCPClient({
    "blocknative-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 Blocknative MCP server via HTTP
  • The client is configured with a name and the URL from our Tool Router session
  • getTools() retrieves all available Blocknative 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 Blocknative 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 Blocknative 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: ['blocknative']
        }
    );

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

Configure Mempool Filters

Tool to configure filters and ABI decoding for Ethereum mempool transactions.

Get Gas Price Distribution

Tool to retrieve the current mempool gas price distribution breakdown.

Get Gas Oracles

Tool to retrieve metadata on supported gas oracles per chain.

Get Gas Prices

Tool to fetch gas price estimates for specific inclusion probabilities.

Get Supported Chains

Tool to retrieve supported chains metadata.

Get Base Fee Estimates

Get real-time gas fee predictions for Ethereum mainnet's next 5 blocks.

Subscribe Multichain

Generate WebSocket connection details to subscribe to real-time blockchain events (transactions or account activity) across multiple chains via Blocknative's Multichain API.

Subscribe Transaction Hash

Tool to subscribe to transaction state change events of an Ethereum transaction hash.

Unsubscribe Multichain

Tool to unsubscribe from events across multiple chains using the Multichain SDK.

Unsubscribe Transaction Hash

Tool to unsubscribe from transaction state change events for an Ethereum transaction hash.

FRAMEWORKS

How to build Blocknative MCP Agent with another framework

OpenAI Agents SDK logo

OpenAI Agents SDK

Use Blocknative MCP with OpenAI Agents SDK

Claude Agent SDK logo

Claude Agent SDK

Use Blocknative MCP with Claude Agent SDK

Claude Code logo

Claude Code

Use Blocknative MCP with Claude Code

Claude Cowork logo

Claude Cowork

Use Blocknative MCP with Claude Cowork

Codex logo

Codex

Use Blocknative MCP with Codex

OpenClaw logo

OpenClaw

Use Blocknative MCP with OpenClaw

Hermes logo

Hermes

Use Blocknative MCP with Hermes

CLI logo

CLI

Use Blocknative MCP with CLI

Google ADK logo

Google ADK

Use Blocknative MCP with Google ADK

Vercel AI SDK logo

Vercel AI SDK

Use Blocknative MCP with Vercel AI SDK

Mastra AI logo

Mastra AI

Use Blocknative MCP with Mastra AI

LlamaIndex logo

LlamaIndex

Use Blocknative MCP with LlamaIndex

CrewAI logo

CrewAI

Use Blocknative MCP with CrewAI

FAQ

Frequently asked questions

With a standalone Blocknative MCP server, the agents and LLMs can only access a fixed set of Blocknative tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from Blocknative 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 Blocknative tools.

Yes, absolutely. You can configure which Blocknative 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 Blocknative data and credentials are handled as safely as possible.

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