LangChain.js and LangGraph

Install

npm install agent402-langchain @langchain/core @langchain/langgraph @langchain/openai zod @x402/fetch @x402/core @x402/evm viem

Example

import { agent402Tools } from "agent402-langchain";
import { ChatOpenAI } from "@langchain/openai";
import { createReactAgent } from "@langchain/langgraph/prebuilt";

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const payClient = new x402Client();
registerExactEvmScheme(payClient, { signer: privateKeyToAccount(process.env.AGENT_KEY) });
const payFetch = wrapFetchWithPayment(fetch, payClient);

// an array of four tools; agent402_call pays search and answer through this fetch
const tools = await agent402Tools({ fetch: payFetch });
const agent = createReactAgent({ llm: new ChatOpenAI({ model: "gpt-4o-mini" }), tools });

const result = await agent.invoke({
  messages: [{ role: "user", content: "Search the web for x402 payment protocol adoption, then answer with citations: what is the x402 payment protocol?" }],
});

No wallet yet? The pure-CPU tools (hash, uuid, base64, markdown, JSON and more) run free with proof-of-work and no wallet:

// the same four tools with no fetch: agent402_call pays pure-CPU tools with proof-of-work
const tools = await agent402Tools();

What it exposes

• agent402_find: a plain-language task in, the best-matching tools out (slug, route, price, input schema, a ready example).
• agent402_route: ranks tools across every indexed x402 seller; include: "external" leaves this server out.
• agent402_call: calls a tool by slug and pays for it.
• agent402_about: the service manifest (payment options, capability map, MCP connector).
• agent402ToolSpecs() returns the same four as framework-agnostic specs (name, description, JSON Schema, execute) with no framework dependency.

How payment works

• Pure-CPU tools: agent402_call fetches a proof-of-work challenge and solves it in-process, so no wallet is needed.
• Wallet-only tools: pass fetch, a payment-wrapped fetch. @x402/fetch pays in USDC over x402 on whichever chain your wallet is funded for; a stock mppx fetch pays over MPP.
• Unpaid lookups (find, route, about) use fetchImpl and never spend anything.

A call that fails is not charged: settlement runs after the tool and only on a successful response. Background: What x402 is · MPP (Machine Payments Protocol).

Tools to try first

Every tool, price and input schema: the catalog.

Links

agent402-langchain on npm · source on GitHub · configuration reference
Guides: One payment, any proven seller: the x402 Smart Order Router · Use Agent402 from Claude Code, Cursor, VS Code, Windsurf, Cline, Roo Code, Codex CLI, Gemini CLI, Muse Code, Continue, ElizaOS, AgentCore and any OpenAI SDK
All integrations