I let AI agents pay my API per call in USDC (x402 on Cloudflare's free plan, zero dependencies)

A developer built and deployed a working pay-per-call API on Cloudflare Pages' free plan that uses the x402 protocol to charge AI agents $0.001–$0.005 in USDC on Base per request, with no npm dependencies, API keys or signup. The service returns an HTTP 402 with machine-readable payment terms, verifies the agent's signed authorization through public facilitators PayAI (with xpay as fallback), runs the handler, and settles only on success so failed calls cost the agent nothing. The developer also validated the flow end-to-end with an empty wallet, confirming the facilitator rejected it solely for insufficient balance.

Disclosure: this post was written with AI assistance and reviewed before publishing. I sell a starter kit based on this code link at the end ; everything below works without buying it. HTTP has had a status code for this since 1997: 402 Payment Required . With the x402 protocol it finally does something. An AI agent calls your endpoint, gets a 402 with machine-readable payment terms, signs a USDC authorization and retries. Then it gets the data. There's no signup, no API key and no Stripe account. I wanted to know how little it takes, so I shipped a real one: freetier-agent-api.pages.dev https://freetier-agent-api.pages.dev . It's one worker.js on Cloudflare Pages free plan with no npm dependencies . GET /api/apis/search?q=weather with no payment returns PAYMENT-REQUIRED header x402 v2 and a JSON body x402 v1, for older clients . Both say: pay 5000 atomic units of USDC = $0.005 on Base to this address. transferWithAuthorization and retries with a PAYMENT-SIGNATURE header. /verify , runs the handler, then calls /settle . The facilitator broadcasts the transfer and pays the gas, and the USDC lands in my wallet. Coinbase's facilitator needs CDP keys on mainnet. Several public facilitators don't: PayAI facilitator.payai.network and xpay facilitator.xpay.sh both settle Base mainnet USDC without auth. I use PayAI and fall back to xpay: js const FACILITATORS = 'https://facilitator.payai.network', 'https://facilitator.xpay.sh' ; async function fac op, body { for const f of FACILITATORS { try { const r = await fetch ${f}/${op} , { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify body } ; const j = await r.json ; if 'isValid' in j || 'success' in j return j; } catch {} } return { error: 'no facilitator' }; } Verify, run, settle, in that order. If the handler fails bad URL, missing parameter , return 400 and never call settle , so the agent pays nothing. This matters, because agents retry a lot. I generated a brand-new empty wallet with viem , signed a correct authorization and sent it to the live API. The facilitator answered invalid exact evm insufficient balance . So the signature, EIP-712 domain USD Coin , version 2 , chain 8453 , amount and recipient were all accepted, and the only thing missing was money. That's a nice zero-cost end-to-end check. A paid API nobody can find earns nothing. What worked: extensions.bazaar with input/output JSON schemas /openapi.json with x-payment-info on each paid operation, plus /.well-known/x402 POST https://api.x402dash.com/v1/register {"url": ...} per endpoint. It probes the 402 live @x402/extensions handles /api/apis/search $0.001 : 2,230 link-checked public and free-tier APIs, with filters like auth=none&alive=yes /api/free-tiers $0.001 : current free-tier limits for dev services and LLM APIs /api/robots-check $0.001 : may user-agent X crawl this URL? /api/page-meta $0.001 : title/OG/headings of a public page respects robots.txt Free: /api/apis/sample , /openapi.json , /health . If you want the cleaned-up code with tests and the listing steps, it's in the x402 Pay-Per-Call Starter https://freetier-kits-shop.fourthwall.com/products/x402-pay-per-call-starter . Or just read the 402 response from the live API and build your own.