x402 + signed receipts
StillOS is an x402 seller: pay-per-call micropayments over plain HTTP, no pre-authorization, no signup. Every paid response is also a cryptographically signed, hash-chained receipt. This page is the real mechanics — for the buyer-facing overview see Platform.
Discover
Agent GETs a StillOS notary endpoint — discovery is always free, no account, no API key. The response describes the resource and its price; nothing is charged for looking.
402
If the free tier for that agent is used up (or the route has none), the server responds HTTP 402 Payment Required, with an x402 accepts[] array: price, asset (USDC), network (Base), and payTo address.
Settle
The agent sends USDC on Base — settlement is instant on-chain, minimum payment $0.01 — and retries the identical request with an X-PAYMENT header carrying proof of payment.
Verify
The server verifies the payment header against the real transaction before doing anything else. A missing, malformed, wrong-amount, or wrong-network payment is rejected outright — it never reaches the paid compute step.
Compute
Only after a verified payment does the server run the actual work — an OFAC screen, a track-record grade, a claim resolution against a named source.
Sign & chain
The response is signed with Ed25519 and hash-chained to the receipt before it, so tampering with any past receipt breaks every signature after it. The receipt, not the raw JSON, is the deliverable.
Payment facts
Machine discovery
An agent doesn't need this page — it needs machine-readable manifests. Start at /.well-known/stillos.json for the service directory, or /notary/catalog for the live, priced endpoint list. Full request/response shapes, error codes, and rate limits are on API Docs.