What is x402? Pay-per-call APIs, explained
x402 is an open standard that lets any web API charge per request, using the HTTP status code 402 Payment Required and a stablecoin such as USDC. No accounts, no API keys, no monthly plans: the price is in the answer, and the client pays for exactly what it uses.
Add it to Claude or Cursor free (30 seconds) See a live answer first
How it works
HTTP has reserved the code 402 Payment Required since the 1990s, but never said how to pay. x402 fills that gap.
- Request. A client (often an AI agent) calls an API as normal.
- Price. The API answers
402 Payment Requiredwith a machine-readable price: how much, in which token, on which networks, paid to which address. - Payment. The client signs a payment authorisation from its wallet and repeats the request with it attached.
- Answer. The API checks the payment, does the work and returns the result. The payment is settled on-chain, usually in seconds, and costs a fraction of a cent in fees.
Why it suits AI agents
- No sign-ups: an agent can use a new API the moment it finds it, without a human creating an account and pasting a key.
- Tiny prices work: a call can cost a fraction of a cent, because there are no card fees and no minimum.
- Pay for what you use: no subscriptions to cancel, and a budget is simply the balance of the agent's wallet.
- Discoverable: services publish their prices and schemas, and directories such as the x402 Bazaar list them.
x402 compared with API keys
With an API key you sign up, add a card, usually pick a plan, and keep a secret. With x402 you need a wallet with a little USDC, and every call carries its own payment. Many services, including ours, offer both: pay per call with x402, or top up prepaid credits and use a key.
For people using Claude or Cursor, neither is needed to start: our MCP server gives 20 free calls a day.
Try it
See a real 402 price for free with one curl (nothing is charged), then follow x402 examples to pay from TypeScript. To find other working x402 services, see the x402 service directory.
curl -i "https://aayatai.com/dns?name=example.com&type=MX"Live example
What a paid call returns: live gas fees
Free, no sign-up: a real answer from our own health check for this input. Your own questions cost $0.002 a call, and the first 20 a day are free in Claude or Cursor.
https://aayatai.com/gas?chains=base%2Cethereum%2Csolana Ask your AI assistant
Once it's added, just ask in plain words. For example:
Find me a working x402 API that checks whether a token is a scam, for under two cents a call.Get a free key and add it All tools and prices
Tools on this page
6 of these 6 are in the free trial (20 calls a day over MCP). Prices come straight from our live price list; failed calls are never charged.
| Tool | What it answers | Price per call |
|---|---|---|
| x402 find | Describe a job in plain English, such as 'scrape a web page to markdown', and get the best working x402 services for it, ranked on fit, real buyers (30 days), our uptime and speed checks, and price, with reasons and how to call each. | $0.002free to try |
| Find the best tool for a job | Find the best tool for a job. | $0.002free to try |
| x402 check | Live health check of any x402 endpoint before you pay it: is it up and answering 402, is the payment request valid, prices in USD per network, pay-to wallets, x402 version, Bazaar discovery metadata, response time, and its buyers in the Bazaar. | $0.002free to try |
| x402 trends | What's growing in the x402 economy: services with the biggest rise in unique buyers over the last N days, from our own daily history of the Bazaar catalogue (history started 2026-09-28 and grows every day), over a window of 1 to 90 days (7 by default). | $0.01free to try |
| DNS | Look up DNS records for any domain: A, AAAA, CNAME, MX, NS, TXT, SOA, CAA, SRV, PTR, DS, DNSKEY, HTTPS, or ALL common types at once. | $0.001free to try |
| Gas fees now (cheapest chain) | Live network fees on Ethereum, Base, Arbitrum, Optimism, Polygon, BNB, Avalanche, Solana and Bitcoin: slow/standard/fast fee rates, congestion and trend, and the USD cost of a send, token transfer and swap on each, plus the cheapest chain now. | $0.002free to try |
Questions people ask
Who created x402?
It was published as an open standard by Coinbase in 2025 and is developed in the open at x402.org, with client libraries anyone can use.
Which tokens and networks does it use?
Mostly USDC, on networks such as Base and Solana. Each service lists what it accepts; ours are in our x402 manifest.
Is my money safe if a call fails?
That depends on the service. Ours only settles a payment after the call succeeds, and rejects bad inputs before you pay.
Do I need crypto to use your tools?
No. In Claude or Cursor you start with free calls, and you can top up prepaid credits instead of paying per call.
Related
- x402 paid API examples: curl, TypeScript and MCP
- x402 service directory: paid APIs that work
- Base gas price right now (and the cheapest chain)
More: every use case · developer docs · llms.txt