x402

Getting started

x402 is an open payment protocol that enables HTTP-native payments. By integrating x402 with AgentMail, your agents can pay for API usage directly over HTTP without managing API keys or subscriptions.

X Layer

Agents on X Layer can pay for API usage directly over HTTP via x402. X Layer is an Ethereum Layer 2 network built with Polygon CDK, offering high throughput and near-zero gas fees.

Base URLs

To authenticate with x402 instead of an API key, you must use the x402-specific base URLs below. These replace the default AgentMail base URLs and route requests through the x402 payment layer.

Prerequisites

• A crypto wallet with USDC funds (EVM-compatible wallet on Base, or a Solana wallet)
• Node.js installed

Install dependencies

$
npm install agentmail @x402/fetch @x402/evm viem

Quickstart

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import { privateKeyToAccount } from "viem/accounts";
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import { x402Client } from "@x402/fetch";
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import { ExactEvmScheme } from "@x402/evm/exact/client";
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import { AgentMailClient } from "agentmail";
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// setup x402 client
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const PRIVATE_KEY = "0x...";
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const signer = privateKeyToAccount(PRIVATE_KEY);
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const x402 = new x402Client();
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x402.register("eip155:*", new ExactEvmScheme(signer));
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// setup AgentMail client
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export const client = new AgentMailClient({ x402 });
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// create inbox
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const inboxRes = await client.inboxes.create({
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  username: `x402-${Date.now()}`,
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});
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console.log("Created inbox: ", inboxRes.inboxId);
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// subscribe to inbox
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const socket = await client.websockets.connect();
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console.log("Connected to websocket");
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socket.on("message", async (event) => {
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  if (event.type === "subscribed") {
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    console.log("Subscribed to", event.inboxIds);
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  } else if (event.type === "event" && event.eventType === "message.received") {
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    console.log("Received message from: ", event.message.from);
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  }
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});
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socket.sendSubscribe({
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  type: "subscribe",
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  inboxIds: [inboxRes.inboxId],
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});

How it works

When you pass an x402 client to AgentMailClient, the SDK automatically handles payment negotiation for each API request. If the server responds with a 402 Payment Required status, the x402 client signs a payment using your wallet and retries the request with the payment attached.

This means your agent can use the full AgentMail API (inboxes, messages, threads, attachments) without needing a traditional API key. Payment happens per-request over HTTP.

Resources

• x402 documentation
• AgentMail API reference
• WebSockets overview