Pay per call, with no account

Pay per call with a wallet and no account. The first answer from a metered route is a quote: HTTP 402 with the price, every way to pay, and what the payment buys. The quote costs nothing (X-Assay-Quote: 1 asks for it without spending a free sample). Pay, and the answer comes back with a receipt you can check without trusting us.

Run 2026-10-11 05:26 UTC against api.s2ar.dev 0.1.1 · 2 calls · 323 ms · list price $0.005 for a stranger (these ran on the operator's key and cost nothing) · every number on this page re-derived by tools/walkthrough.py before it was written

1. The quote: HTTP 402

Everything an agent needs to decide is in the body: the price, the rails, the evidence it will get, the refund rule, and where the rules and the record of how we kept them live.

curl -s -X POST 'https://api.s2ar.dev/v1/sym/read' \
  -H 'X-Assay-Quote: 1' \
  -H 'content-type: application/json' \
  -d '{"repo": "https://github.com/BurntSushi/ripgrep", "ref": "14.1.1", "file": "crates/core/flags/defs.rs", "symbol": "Glob as Flag"}'

→ HTTP 402 · 147 ms

{
  "price_usd": 0.005,
  "rails": [
    "x402",
    "credits"
  ],
  "accepts.0.scheme": "exact",
  "accepts.0.network": "base",
  "accepts.0.asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "accepts.0.maxAmountRequired": "5000",
  "accepts.0.payTo": "0x2c4938626788e8e4fd803bfd1353eca64c1b5452",
  "accepts.0.extra": {
    "name": "USD Coin",
    "version": "2"
  },
  "evidence": "assay",
  "determinism": "replayable",
  "witnesses": [],
  "expected_latency_ms": 400,
  "refund_rule": "a paid call that is not delivered is credited automatically and counted in the proceedings",
  "free.per_day_keyless": 10,
  "charter": "https://api.s2ar.dev/charter",
  "proceedings": "https://api.s2ar.dev/.well-known/proceedings.json"
}

2. The paid answer and its receipt

The receipt’s evidence_hash is sha256 over the canonical answer (sorted keys, compact), so the buyer can recompute it from what they received. The generator did, below.

curl -s -X POST 'https://api.s2ar.dev/v1/sym/read' \
  -H "Authorization: Bearer $S2AR_KEY" \
  -H 'content-type: application/json' \
  -d '{"repo": "https://github.com/BurntSushi/ripgrep", "ref": "14.1.1", "file": "crates/core/flags/defs.rs", "symbol": "Glob as Flag"}'

→ HTTP 200 · 176 ms · list price $0.005 · receipt sha256:598d5e19ec2bace6…

{
  "tokens_est": 565,
  "receipt.evidence_hash": "sha256:598d5e19ec2bace68778add369e74f054ca7dc43c2583e0e1e0c4cbefa58a832",
  "receipt.what": "read",
  "receipt.determinism": "replayable",
  "receipt.witnesses": [],
  "receipt.refund_rule": "a paid call that is not delivered is credited automatically and counted in the proceedings",
  "x-assay-receipt": "sha256:598d5e19ec2bace68778add369e74f054ca7dc43c2583e0e1e0c4cbefa58a832"
}

The quote lists only the rails that can settle right now. When the x402 rail is open it adds an x402 offer: USDC on Base, in both protocol versions (the v1 JSON body and the v2 PAYMENT-REQUIRED header), with the token’s signing domain, settled through Coinbase’s facilitator only after the answer exists. Directories and facilitators probe the /x402/… mirror of each route, which answers every unpaid request with this quote. Credits (a key bought once, good on every s2ar route) work today; from $0.50, so does Stripe’s Machine Payments Protocol.

What this cannot buy

From the signed proceedings (/.well-known/proceedings.json), verbatim:

• placement or routing position
• a different verdict or grade
• buyer data
• amendment access
• a revocation

Failed calls are never charged. Nothing about a caller is kept. The rules: the charter.