x402 Payments skill

x402 turns HTTP 402 Payment Required into a real payment rail for agents: a server replies 402 with what it wants paid; the client signs an off-chain authorization and retries with an X-PAYMENT header; a facilitator broadcasts it. Settlement uses EIP-3009 transferWithAuthorization (e.g. USDC on Base) — the facilitator can only broadcast the signed authorization, never alter the amount or destination.

Custody-free: the plugin builds the EIP-712 the payer signs and assembles the header; it never holds a key.

Tools

Tool	Purpose
chaingpt_x402_decode	Decode a 402 body or X-PAYMENT header into human terms (amount/token/recipient/expiry) before paying.
chaingpt_x402_build_payment	Build the UNSIGNED EIP-3009 typed data; pass a signature back to get the final X-PAYMENT header.
chaingpt_x402_facilitator	Call a facilitator: supported / verify / settle.
chaingpt_x402_create_requirements	Server side: generate the PaymentRequirements + 402 body to monetize your endpoint.
chaingpt_x402_fetch	The whole client loop in one tool: fetch a URL; on 402 it decodes the challenge and (given from) emits the unsigned typed data; re-call with xPaymentHeader to complete the paid request.

Pay an endpoint (client flow)

Fast path — one tool drives the loop:

1. chaingpt_x402_fetch url=<resource> from=<payer> → on 402 you get the decoded price/payee AND the unsigned EIP-3009 typed data.
2. Sign the typed data in the payer's wallet.
3. chaingpt_x402_build_payment from=<payer> requirements=<from step 1> signature=0x… → the X-PAYMENT header.
4. chaingpt_x402_fetch url=<resource> xPaymentHeader=<header> → the paid response.

Manual path (same primitives, finer control): _decode → _build_payment → sign → _build_payment +signature → retry yourself.

Monetize your endpoint (server flow)

chaingpt_x402_create_requirements network=base amount=0.01 payTo=<you> → serve the returned JSON with HTTP 402. Verify/settle incoming payments via a facilitator (chaingpt_x402_facilitator).

Known EIP-3009 tokens: USDC on base and base-sepolia. For other tokens pass full PaymentRequirements (with asset + extra.name/extra.version). 0 ChainGPT credits.