Extensions

Builder Code

See which app surfaced your paid API and which facilitator settled the payment—useful for revenue share, partner reporting, and ecosystem analytics.

Why use it

  • Attributes settlement on chain to the integration that exposed the endpoint.
  • Keeps core payment types unchanged; attribution rides alongside normal verify and settle.

How it works

  • Your server includes builder attribution in the payment-required response when you support this extension.
  • The facilitator that settles can append standardized attribution data to settlement calldata.

Highlighting Request

  1. Request

    Wallet, agent, or app that selects an offer and signs payment.

    GET
    GET

    Sells access and publishes payment requirements.

    GET

    Verifies signatures and submits chain transactions on behalf of merchants.

  2. 402

    Your server includes builder attribution in the payment-required response when you support this extension.

    Wallet, agent, or app that selects an offer and signs payment.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    { "x402Version": 2 }

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Sells access and publishes payment requirements.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Verifies signatures and submits chain transactions on behalf of merchants.

  3. Pay and retry

    Wallet, agent, or app that selects an offer and signs payment.

    PAYMENT-SIGNATURE
    PAYMENT-SIGNATURE

    Sells access and publishes payment requirements.

    PAYMENT-SIGNATURE

    Verifies signatures and submits chain transactions on behalf of merchants.

  4. Verify

    Wallet, agent, or app that selects an offer and signs payment.

    Sells access and publishes payment requirements.

    verify
    verify

    Verifies signatures and submits chain transactions on behalf of merchants.

    verify

  5. Settle

    Wallet, agent, or app that selects an offer and signs payment.

    Sells access and publishes payment requirements.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

    Verifies signatures and submits chain transactions on behalf of merchants.

    Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

  6. Response

    Wallet, agent, or app that selects an offer and signs payment.

    200
    200

    Sells access and publishes payment requirements.

    200

    Verifies signatures and submits chain transactions on behalf of merchants.

Learn more

Read the extension spec (opens in a new tab)Extension docs (opens in a new tab)
For engineers

Extension key builder-code.

Resource server supplies builder identifiers in extension info; the settling facilitator appends ERC-8021 Schema 2 (CBOR-encoded) suffix data defined in the spec.

  • Extension key: builder-code on PaymentRequired extensions.
  • Schema 2 suffix: ercMarker, schemaId 0x02, cborLength, cborData at end of calldata.
  • Custom registries (r) are not supported; facilitator-owned metadata field m is facilitator-written.