What Is x402? The Payment Standard AI Agents Actually Need
HTTP status code 402 has been reserved since 1999. x402 is the protocol that finally gives it meaning — enabling AI agents to pay for API calls with on-chain USDC, no credit card or human required.
The Problem x402 Solves
Every API today assumes a human set it up. Someone created an account, entered a credit card, generated an API key, and loaded credits. When AI agents need to call APIs autonomously, this breaks down completely.
Agents cannot click email verification links. They cannot enter a credit card number. They cannot log in. The entire payment and auth stack was designed for humans — not autonomous software.
x402 fixes this. An agent can call any x402-enabled API, receive payment instructions, pay with on-chain crypto, and get the result — all in a single request cycle with no human involvement.
How x402 Works
Agent calls the API
No credentials. Just a standard HTTP request to the endpoint.
Server returns 402 with payment instructions
Price in USDC, wallet address, supported chains, resource URL — all in the response body.
Agent submits payment on-chain
USDC on Base or Polygon. Transaction completes in seconds.
Agent retries with payment proof
Same request, now with an X-Payment header containing the signed transaction hash.
Server verifies and responds
Payment verified against the facilitator, response returned. Done in under 2 seconds total.
Supported Chains on Arch Tools
Why Arch Tools?
Arch Tools is the first API platform to wire x402 into every endpoint. 63 production tools — AI generation, web scraping, crypto data, OCR, NLP, browser automation — all accessible via credit card for humans or x402 crypto payments for agents.
We also filed the first patent for an AI agent identity and authorization protocol (Patent #64/008,145, March 2026) — a ground-up rethink of how autonomous agents authenticate without human-managed credentials.
Try x402 on Arch Tools
100 free credits on signup — 25 instant, 75 on email verify. No card required. Start making agent-native API calls in minutes.
Try the x402 Playground