X402

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= from= → 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= requirements= signature=0x… → the X-PAYMENT header.
4. chaingpt_x402_fetch url= xPaymentHeader= → 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= → 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.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: ChainGPT-org
• Source: ChainGPT-org/chaingpt-claude-skill
• License: MIT
• Homepage: https://docs.chaingpt.org/dev-docs-b2b-saas-api-and-sdk

Install and usage instructions live in the source repository linked above.