Make AI agents pay your API per call — one command, no API keys (x402 + USDC)

AI agents can't sign up for your API. They can't fill in a billing form, verify an email or paste a key into a dashboard. But they can hold a wallet and sign a payment.

That's what x402 is for. It's the HTTP 402 Payment Required status code, finally put to use. Your server answers a request with 402 and a price. The agent signs a USDC payment and retries. Your server settles the payment and returns the content. No accounts, no keys, no invoices.

This post shows the fastest way I know to ship it: one command that builds a paid API, a paid MCP server or a paid file store. It runs on Express, Hono, Next.js, Cloudflare Workers or FastAPI.

npm create @scriptmasterlabs/x402 my-api Enter fullscreen mode Exit fullscreen mode No global install. Prefer to run it straight from source? npx gitlab:script-master-labs-llc-group/x402-kit my-api or npx github:Timwal78/x402-kit my-api do the same thing.

Pick a stack with --stack express | hono | next | workers | fastapi.

npm create @scriptmasterlabs/x402 my-mcp -- --stack express --mode mcp --pay-to 0xYourWallet --price 0.01 cd my-mcp npm install npm start Enter fullscreen mode Exit fullscreen mode --pay-to is the wallet that receives USDC on Base. Payments go straight to it; the facilitator never holds your money. If you leave it out, paid routes answer 503 seller_not_configured until you set PAY_TO in.env. The kit never falls back to a placeholder wallet.

curl -i -X POST localhost:3000/mcp -H 'content-type: application/json' \ -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"text_stats","arguments":{"text":"hello agents"}}}' Enter fullscreen mode Exit fullscreen mode HTTP / 1.1 402 Payment Required PAYMENT-REQUIRED: eyJ4NDAyVmVyc2lvbiI6Mi... Enter fullscreen mode Exit fullscreen mode The challenge, which says what to pay, how much, in what asset and to which wallet, is in the JSON body and in the base64 PAYMENT-REQUIRED header. Any standard x402 client can read it, sign, and retry with a PAYMENT-SIGNATURE header.

The free tool ( ping ) answers right away. tools/list labels the paid tools with their price, so agents know before they call.

export const tools = [ { name: ' ping ', description: ' Free health check. ', handler: async () => ({ ok: true }), }, { name: ' text_stats ', description: ' Word, sentence and character counts plus the top words. ', priceUsd: ' 0.01 ', // remove this line and the tool is free inputSchema: { type: ' object ', properties: { text: { type: ' string ' } }, required: [ ' text ' ] }, handler: async ({ text }) => { /*... */ }, }, ]; Enter fullscreen mode Exit fullscreen mode If a handler throws, the caller gets a tool error and is not charged. The kit only settles a payment after your code succeeds.

Fund a throwaway wallet with a little USDC on Base, then:

BUYER_PRIVATE_KEY = 0x<throwaway wallet> npx @scriptmasterlabs/create-x402 pay http://localhost:3000/mcp \ --method POST --data '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"text_stats","arguments":{"text":"hello agents"}}}' Enter fullscreen mode Exit fullscreen mode pay uses the stock x402 Foundation client ( @x402/fetch + @x402/evm ). It reads the 402, refuses anything above --max-usd (default $0.05), pays, and prints the settlement transaction with a Basescan link.

Then open http://localhost:3000/x402/receipts. Every settled payment is listed there with its transaction hash.

npm create @scriptmasterlabs/x402 my-proxy -- --stack hono --mode wrap \ --upstream https://api.yourservice.com --pay-to 0xYourWallet --price 0.02 Enter fullscreen mode Exit fullscreen mode Every request is proxied to your upstream after payment. In.env you can:

npx @scriptmasterlabs/create-x402 add Enter fullscreen mode Exit fullscreen mode This drops a dependency-free core into your project, plus an X402.md with the wiring:

// Express app. get ( ' /report ', paid ( x402, ' 0.02 ', ' One full report ' ), handler ); // Hono / Next.js route handlers / Cloudflare Workers return x402. protect ( request, { priceUsd: ' 0.02 ' }, () => Response. json ( data )); Enter fullscreen mode Exit fullscreen mode Python projects get x402_seller.py with await x402.protect(request, "0.02", "One report", handler).

Every generated project ships an AGENTS.md. Give Claude Code or Cursor one sentence:

Run npm create @scriptmasterlabs/x402 my-api to make my API charge AI agents per call, then follow the generated AGENTS.md.

A facilitator verifies the signed payment and broadcasts it on-chain. The kit's default is OMNIGATE ( https://mcp-x402.onrender.com ), the facilitator my company, Script Master Labs, runs for USDC on Base and Arc.

FACILITATOR_URLS=https://your-current-facilitator.example,https://mcp-x402.onrender.com Enter fullscreen mode Exit fullscreen mode How it was tested Before publishing, every stack and mode was scaffolded and paid with the stock x402 client against the live facilitator, plus a real $0.01 USDC settlement on Base through a kit-built app. Both wallets in that settlement were ours, so it proves the kit works end to end, not that anyone else uses it yet.

npm: @scriptmasterlabs/create-x402 · Repo and issues: https://gitlab.com/script-master-labs-llc-group/x402-kit (GitHub copy: https://github.com/Timwal78/x402-kit )

If you build something with it, I'd like to see it.