Demo Walkthrough with real transactions
An autonomous agent buys a EUR/USD quote for one cent from a bonded API, catches the seller quoting 10% away from the oracle, and is paid 5 USDC from the seller's stake in a single claim. Every step below happened on-chain, and every transaction is linked so you can verify it yourself.
01 The cast
The seller and the agent are ordinary x402 participants. The Bond Registry, the Claims contract and the validators are what LOPW adds. None of them needs a human to act.
Sells EUR/USD quotes for one cent each and warrants five predicates against its own stake.
Runs the LOPW buyer SDK. It reads the bond before paying and refuses any service that falls short of its policy.
Holds the seller's stake, its registered terms and signing key. Slashes only on instruction from the Claims contract.
Checks signatures, the claim window and double claims, asks the right validator, then pays the buyer or rejects.
One per predicate. P6 reads the SEP-40 oracle on-chain, so the seller cannot influence the verdict.
02 Walkthrough
Play it, or step through it at your own pace. The console shows the demo agent's real output; the grey lines underneath explain what happened on the wire and on-chain at each step.
The agent asks the seller what it warrants. The listing names the service and the bond behind it.
GET https://fx.lopw.com/v1/warranty
{
"service_id": "a1f1c5c89c63…",
"state": "Active",
"stake": "2000000000" // 200 USDC, 7 decimals
}
The agent does not take the seller's word for it. It reads the Bond Registry directly: the service is Active and 200 USDC of stake stands behind it.
BondRegistry.get_service(a1f1c5c89c63…)
state Active
stake 200.00 USDC
terms_hash 69d78803…
predicates P1 P2 P3 P4 P6
The agent asks for a quote. The seller answers 402 Payment Required with the usual x402 terms, plus a signed LOPW offer in extensions.lopw that pins the registered terms by hash.
GET /v1/quote?pair=EUR-USD ← 402 Payment Required { "x402Version": 2, "accepts": [{ "scheme": "exact", "price": "$0.01", … }], "extensions": { "lopw": { "service_id": "a1f1c5c89c63…", "registry": "CD32WBJS…", "terms_hash": "69d78803…", "price": { "amount": "100000", "display": "$0.01" }, "max_claim": "50000000", // 5 USDC "valid_until": …, "offer_nonce": "…", "key_version": …, "signature": "…" } } }
Before paying, the buyer SDK checks the offer against the chain and against the agent's own policy. If any check fails, it walks away without paying.
offer signature registered key ✓ service state Active ✓ stake ≥ minStake 200.00 ≥ 100.00 USDC ✓ covers P6 P1 P2 P3 P4 P6 ✓ max_claim ≥ 1 USDC 5.00 USDC ✓ fresh offer valid_until, new nonce ✓
Payment is ordinary x402: the agent signs a USDC transfer and the facilitator verifies and settles it on-chain. Nothing is held in escrow.
GET /v1/quote?pair=EUR-USD PAYMENT-SIGNATURE: { "x402Version": 2, "scheme": "exact", … } facilitator verify ✓ settle ✓ transfer 0.01 USDC agent → seller
The seller returns the quote and a signed receipt in PAYMENT-RESPONSE that binds the payment, the request, the response bytes and the terms. The rate is 10% below the oracle: this seller runs with FAULT=BAD_PRICE.
HTTP/1.1 200 OK {"pair":"EUR-USD","rate":"1.01258970","rate_raw":"101258969676705","decimals":14,"as_of":1790993400} PAYMENT-RESPONSE → extensions.lopw = { "service_id": "a1f1c5c89c63…", "offer_hash": "…", "terms_hash": "69d78803…", "buyer": "GDO5YT…", "payment_reference": "93787e82b69d…", "request_hash": "…", "response_hash": "…", "status": 200, "response_bytes": …, "served_at": …, "data_as_of": …, "oracle": { "reported_value": "101258969676705", … }, "signature": "…" }
The agent checks that the receipt is genuine and is about this purchase. A receipt that fails here is flagged untrusted: no claim can be made on it, and the seller is not penalised.
signature service key at key_version ✓ offer_hash the offer that was paid ✓ buyer GDO5YT… (this agent) ✓ payment_reference 93787e82b69d… settlement ✓ request_hash SHA-256 of the request sent ✓ response_hash SHA-256 of the bytes received ✓
The SDK evaluates every predicate in the terms locally. P6 compares the reported rate with the SEP-40 oracle price the receipt cites: 10% apart, against a promised 0.5%.
P1 equivocation one receipt for this payment kept P2 terms receipt terms = offer terms kept P3 freshness within max_data_age kept P4 status 200 is chargeable kept P6 oracle reported 1.01258970 oracle ≈1.12509966 EUR/USD deviation 1000 bps > 50 bps BREACH
The agent submits the signed offer and receipt to the Claims contract. Anyone may file; the payout always goes to the buyer named in the receipt.
Claims.claim(predicate: 6, offer, receipt) service not Closed ✓ offer and receipt signatures ✓ receipt cites the offer ✓ inside served_at + 1 h window ✓ payment not claimed before ✓ P6 listed in the terms ✓
Claims hands the evidence to the P6 validator, which reads the oracle price at the cited timestamp on-chain and decides from that alone. No one votes and no one reviews.
ValidatorP6.validate(offer, receipt, terms) oracle.price(EUR, oracle_timestamp) // SEP-40, on-chain |reported − oracle| × 10000 > 50 × oracle → Proven
The Claims contract instructs the Bond Registry to slash. The payout is min(max_claim, stake left): 5 USDC, transferred to the buyer in the same transaction.
BondRegistry.slash(a1f1c5c89c63…, 5.00 USDC) event ClaimPaid { predicate: 6, amount: 50000000 } stake 200.00 → 195.00 USDC state Active
The buyer holds 5 USDC more and the seller's bond is 5 USDC lighter, still Active. The whole claim is one transaction anyone can open.
agent +5.00 USDC
seller stake 195.00 USDC (Active)
tx 9b10abc505b952fccf9b8dd02eef0d12
3600ac2783b279098aa38c21b6911a4a
Open this claim on Stellar Expert ↗
Live Scenario log
This walkthrough and its siblings run on a schedule against the live services with real payments; the two latest runs of each are below, and the full history is on the proofs page.
The scenario log is read live from the LOPW API. What each scenario checks, why it matters and how a run is judged is described in Proofs and scenarios in the documentation.
03 On-chain proof
The same agent ran against seller faults covering all six predicates. Each breach was proven by its validator contract and paid from stake. Open any row to see the transaction.
| Predicate | What the seller did wrong | Fault | Payout | Transaction |
|---|---|---|---|---|
| P1 EquivocationFX quote API | Signed two different receipts for the same payment | DUPLICATE_RECEIPT | 5 USDC | 3cfe29e4…1b7da282 ↗ |
| P2 Terms mismatchFX quote API | Receipt cited the offer but different terms | WRONG_TERMS | 5 USDC | 7ca5efcf…9048589de2 ↗ |
| P3 Stale dataFX quote API | Served a quote an hour old against a 10-minute limit | STALE_DATA | 5 USDC | 0ef85a5d…5e42bafcb5 ↗ |
| P4 Bad statusLedger data API | Charged for HTTP 203 when only 200 is chargeable | BAD_STATUS | 1 USDC | 54c2e8f6…e95788e990 ↗ |
| P5 Size limitLedger data API | Returned a response over the 4 KiB limit | OVERSIZE | 1 USDC | b6f33404…2f79f4bc ↗ |
| P6 Oracle deviationFX quote API | Quoted EUR/USD 10% off the SEP-40 oracle; tolerance 0.5% | BAD_PRICE | 5 USDC | 5d75c3a0…c21b6911a4a ↗ |
| Tampered receipt | Receipt signature does not verify | BAD_SIGNATURE | Untrusted | No claim possible, no penalty |
| Honest response | Nothing | NORMAL | Kept | Warranty kept, nothing to claim |
ClaimPaid event and the USDC transfer to the buyer. P1, P2, P3 and P6 were paid by the FX quote API (5 USDC per receipt); P4 and P5 by a ledger data API bonded with a 1 USDC payout per receipt.04 The contracts
Eight contracts did the work above. Each address opens on the Stellar Expert explorer for the Stellar testnet, where you can inspect its storage, calls and events.
Stake, terms and signing keys per service. Slashes on instruction from Claims.
CBNGZB5GL3FEZKIQK73BTJYCQAC76N7SZCLN34JRMTQCUWER4GB3WHPL ↗Verifies the evidence, calls the validator, records the outcome and triggers the payout.
CBUBZC2AHVKFKYTAO3DIF6CZFQVM4UYCNABYVTPQNUUJGLOIBSIWONSC ↗Live From the indexer
Read live from the LOPW indexer API, which follows the Bond Registry and Claims contracts event by event.
05 Run it yourself
The demo agent is a short script on top of the buyer SDK. Point it at the FX quote API, choose a fault, and it prints the console above with a transaction hash of its own.
AGENT_SECRET=... SERVICE_URL=https://fx.lopw.com FAULT=BAD_PRICE pnpm --filter @lopw/demo-agent startAGENT_SECRET is the agent's Stellar secret key; the account needs USDC on the same network as the contracts above. FAULT asks the seller to misbehave in one specific way:
BAD_PRICEQuote 10% off the oracle → P6STALE_DATAQuote an hour old → P3WRONG_TERMSReceipt cites other terms → P2DUPLICATE_RECEIPTSecond receipt for one payment → P1BAD_SIGNATURETampered receipt → untrusted, no claimNORMALHonest response → warranty keptimport { LopwBuyer } from "@lopw/buyer-sdk";
const agent = new LopwBuyer({
secret: process.env.AGENT_SECRET,
policy: {
minStake: 100n * 10_000_000n, // 100 USDC
requiredPredicates: [6],
minMaxClaim: 10_000_000n, // 1 USDC
},
});
const { response, body, warranty } = await agent.fetch(
"https://fx.example.com/v1/quote?pair=EUR-USD"
);
if (warranty?.breaches.length) {
const result = await agent.claim(warranty);
// { outcome: { paid }, transaction }
}