x402 Delivery-Guarantee — Open Spec v0.1

Testnet proven · Mainnet next

A practical, shipped, open format for verifiable delivery + on-chain money-back guarantee on x402 services. Reference implementation live on nsgoods (proof-of-delivery on 4 endpoints; guarantee proven end-to-end on Base Sepolia). CC BY 4.0. Status: testnet-proven, mainnet next.

Two components

Proof-of-Delivery (off-chain, live): every paid response carries a signed Ed25519 receipt an agent can verify independently (GET /proof/pubkey, POST /proof/verify per service).
Delivery-Guarantee (on-chain, testnet): a seller posts a USDC bond; if a call's verdict is FAILED, the buyer is paid from the bond. A neutral verifier signs the verdict. No custody by the verifier, not insurance.

Proof-of-Delivery receipt (pod-0.1)

Attached as _proof on each paid JSON response. Fields:

v, service, ts, request_hash, response_hash, latency_ms, http_status, checks{http_200,non_empty,schema}, missing_fields, verdict (DELIVERED|FAILED), key_id, alg=Ed25519, signature.

Signed over canonical JSON (sort_keys, no spaces) minus signature.

Verdict rule (objective only): DELIVERED iff http_200 AND non_empty AND schema (all declared required_fields present & non-empty). Content correctness/quality is out of scope.

On-chain Delivery-Guarantee

Contract GuaranteeBond (Base). Roles: seller (posts bond), buyer (receives), verifier (signs verdicts).

Flow: depositBond → paid call → verifier determines DELIVERED/FAILED → on FAILED, verifier signs EIP-712 Claim → claim() pays amount from seller's bond to buyer. Replay-guarded per callId, expiry-bound.

EIP-712:

domain name="x402Guarantee" version="1"; Claim(bytes32 callId, address seller, address buyer, uint256 amount, uint8 verdict, uint256 expiry); verdict 0=DELIVERED 1=FAILED.

Solo-safe / not insurance: the contract holds funds (not the verifier); payout is from the seller's own bond (no underwriting); the verifier only signs a verdict. Collateralized performance bond + neutral oracle.

Scope (locked)

Objective delivery only (HTTP 200, valid schema, within SLA). Not content correctness. Deterministic/checkable services first.

How a third party consumes this

Any scorer/registry/insurer/marketplace can verify a receipt with /proof/pubkey (no trust in the seller), consume the DELIVERED/FAILED verdict as evidence, and reference bonded status as a trust signal. Composes with endpoint-reputation scoring: scorer says "is the endpoint legit"; this says "did this call provably deliver, and is it bonded".

Status & limits

Testnet-proven; not live on mainnet for real money yet. Framing: "proven on testnet / mainnet next". Demand for guarantees is early (~2027-28). Open by design (CC BY 4.0).