Pay an API with x402 — in about ten lines

x402 is HTTP 402 put to work: a server answers 402 Payment Required with the exact price, the client signs a stablecoin payment and repeats the same request. No account, no API key, no invoice.

These examples call DexL Agents, an x402 gateway (chat models, speech, web search and crawl, on-chain reads, FX rates, NLP tools). Everything here works against any x402 server — only the URL changes.

1. Free: no wallet at all

Terminal

npm install
npm run free

free.mjs does two things:

calls the free tier (model: "dexl-free") — no payment header, no wallet, no account;
asks what a paid call would cost by sending it without payment and reading the 402.

Real output:

Code

free answer: HTTP 402 (Payment Required) is a non-standardized status code reserved for future use...
web-search costs 0.01 USDC on eip155:8453 (HTTP 402)

2. Paid: one call, one signature

bash

PRIVATE_KEY=0x... npm run paid

The payment is these three lines; after them it is ordinary fetch:

server.ts

const signer = toClientEvmSigner(wallet);
const client = new x402Client().register('eip155:8453', new ExactEvmScheme(signer));
const fetchWithPay = wrapFetchWithPayment(fetch, client);

Your key stays on your machine — the server only ever sees a signed payment. Settles in USDC on Base, Polygon, Arbitrum or Solana. Error responses are not charged.

The free example above was run as-is. The paid one needs your own funded wallet, so run it yourself with a small balance; it uses the same client our own service uses.

3. Connect an MCP client

Remote (free tools only — a remote server holds no wallet of yours):

Code

https://agents.dexl.io/mcp

Local, with paid tools, because the wallet stays on your machine:

config.json

{
  "mcpServers": {
    "dexl": {
      "command": "npx",
      "args": ["-y", "dexl-agents", "mcp"],
      "env": { "DEXL_BASE_URL": "https://agents.dexl.io", "DEXL_PRIVATE_KEY": "<optional>" }
    }
  }
}

What you can call

GET /v1/tools lists every tool with its price and schema. Machine-readable: /llms.txt · /openapi.json · /.well-known/x402 · /.well-known/mcp

MIT licensed. Issues and pull requests welcome.