Why they exist
Core x402 stays small and chain-agnostic. Extensions let the ecosystem ship new buyer and seller experiences without rewriting the base protocol. You implement only the extensions your product needs.
Highlighting Request
Request
Wallet, agent, or app that selects an offer and signs payment.
Core x402 stays small. Extensions are optional.
Core x402 stays small. Extensions are optional.
Core x402 stays small. Extensions are optional.
Sells access and publishes payment requirements.
Core x402 stays small. Extensions are optional.
Verifies signatures and submits chain transactions on behalf of merchants.
402
Extensions are named keys on the v2 payment-required payload.
Wallet, agent, or app that selects an offer and signs payment.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
{ "x402Version": 2 }Sells access and publishes payment requirements.
Each extension entry pairs info with a JSON Schema. They do not change the amount or the scheme.
Verifies signatures and submits chain transactions on behalf of merchants.
Pay and retry
Wallet, agent, or app that selects an offer and signs payment.
Clients attach extension data only when the server advertised it.
Clients attach extension data only when the server advertised it.
Clients attach extension data only when the server advertised it.
Sells access and publishes payment requirements.
Clients attach extension data only when the server advertised it.
Verifies signatures and submits chain transactions on behalf of merchants.
Verify
Wallet, agent, or app that selects an offer and signs payment.
Sells access and publishes payment requirements.
Some extensions stop at the server and client. Others include the facilitator.
Some extensions stop at the server and client. Others include the facilitator.
Some extensions stop at the server and client. Others include the facilitator.
Verifies signatures and submits chain transactions on behalf of merchants.
Some extensions stop at the server and client. Others include the facilitator.
Settle
Wallet, agent, or app that selects an offer and signs payment.
Sells access and publishes payment requirements.
Settlement itself stays on the payment scheme.
Settlement itself stays on the payment scheme.
Settlement itself stays on the payment scheme.
Verifies signatures and submits chain transactions on behalf of merchants.
Settlement itself stays on the payment scheme.
Response
Wallet, agent, or app that selects an offer and signs payment.
The resource response is unchanged.
The resource response is unchanged.
The resource response is unchanged.
Sells access and publishes payment requirements.
The resource response is unchanged.
Verifies signatures and submits chain transactions on behalf of merchants.
Topics on this site
CDP Bazaar
Get your paid API discovered by agents through Coinbase Developer Platform's Bazaar catalog.
Read overview →Builder Code
See which app surfaced your paid API and which facilitator settled the payment—useful for revenue share, partner reporting, and ecosystem analytics.
Read overview →Sign In With X
Recognize returning wallets so repeat customers can skip paying again when your policy allows it—without replacing normal x402 payment verification.
Read overview →EIP2612 Gas Sponsoring
Buyers can approve Permit2 spending without holding ETH for gas—the facilitator submits the EIP-2612 permit when settling.
Read overview →ERC-20 Gas Sponsoring
Support gasless Permit2 approval for any ERC-20—even tokens without EIP-2612—so buyers are not blocked for lacking ETH.
Read overview →Payment Identifier
Let clients attach a stable idempotency key so repeat submissions return the same outcome instead of double-charging or double-fulfilling.
Read overview →
For engineers
On the wire, extensions appear as named keys on v2 payment-required payloads. Each entry pairs info (data) with a JSON Schema for info.
- Canonical definitions live under specs/extensions/ in the x402 repository.
- Integration guides for several extensions live under docs/extensions/.
