Specification · c402/1

The c402 protocol

c402 is a confidential compute layer that sits on top of x402 the same way x402 sits on top of HTTP. It adds exactly two headers. Everything else - what the computation is, what the inputs and outputs mean - is defined by the server.

HTTPgive me a resource

request / response

x402pay to access a resource

402 + PAYMENT-REQUIRED

c402pay to access a private thought

x402 + 2 headers

Two headers

Compute-Requiredon the 402

Describes the confidential computation: the TEE standard, the on-chain compute contract, the input schema/encoding, and the output schema. The client reads it to know what to encrypt and what to expect.

X-Attestationon the paid 200

Proves the TEE executed. Every field is a real, independently re-verifiable on-chain artifact - decisionId, commitment, registry, tx, output handles. No fabricated quotes.

Reference packages

@c402/spec

The protocol in code: constants, types, header codecs, SPEC.md, JSON schema.

@c402/server

c402(config) Express middleware - declare a confidential paid endpoint in one call.

@c402/client

c402Fetch(opts) - pay, consume, and verify an attestation as one fetch.

@c402/verify

Standalone on-chain attestation verifier anyone can run.

Trustless verification

The attestation is not a trust-us blob: it points at an on-chain commitment. A verifier re-reads that commitment from the registry on the declared network and confirms it matches, with no cooperation from the server. Try it on a real decision:

Verify a decision →Inspect a live endpoint

Full specification: packages/c402-spec/SPEC.md · JSON schema: packages/c402-spec/schema/attestation.schema.json