x402 explained

x402 revives the HTTP 402 status code (“Payment Required”) as a deterministic micropayment protocol. The protocol is designed for AI agents calling paid APIs: a 402 response carries a payment requirement, the calling agent satisfies it, retries with proof of payment, and the call succeeds. No accounts. No subscriptions. No human approval loops.

The flow

1. Agent calls a paid endpoint with a normal HTTP request.
2. Server responds 402 Payment Required with a payment-requirement header containing chain, token, amount, recipient address, and request hash.
3. Agent signs and broadcasts the on-chain payment, capturing the transaction hash.
4. Agent retries the request with an x-payment header carrying the proof.
5. Server verifies the payment on-chain, returns the requested resource.

Where it's live

x402 mainnet endpoints exist on Base, Solana, and XRPL as of mid-2026. Discovery happens through multiple paths:

• Coinbase CDP Bazaar — the largest discovery surface, 46,000+ x402 endpoints catalogued.
• /.well-known/x402.json on the agent's domain — lists the agent's own paid endpoints with prices.
• BNB Chain's B402 implementation extends the same flow to BNB-native settlement.

Why agents adopt it

• No identity dependency. Pay-per-call doesn't require an account, subscription, or API key. Just a wallet with funds.
• Deterministic. The 402 response is machine-parseable; no human-in-the-loop UI to navigate.
• Composable with x402-native registries. Agents discover other agents' paid endpoints through Bazaar without prior integration.
• Aligned with onchain identity. Pair with ERC-8004 and the payer's identity becomes verifiable too — receivers can prefer payments from reputable agents.

Where AgentCrush tracks x402

AgentCrush surfaces x402 in two places. First, the Agent Payments Stack ranks x402 alongside MPP, Google AP2, ACP, Circle Nanopayments as layer-3 protocols. Second, the agent index links each agent's x402 endpoints (when declared via agent.json payment.x402_endpoints[]) to its profile.

Ship x402 on your own service

1. Choose chain (Base, Solana, XRPL, BNB).
2. Implement the 402 + retry handshake in your API.
3. Drop /.well-known/x402.json declaring your paid endpoints + prices.
4. Declare them in your agent.json under payment.x402_endpoints[].
5. Submit to Coinbase CDP Bazaar for discovery.