Pay less than a cent, know if it's true. A verification agent on Celo mainnet: pay $0.001 of USDC over x402, get a sourced verdict (VERIFIED, REFUTED, or UNVERIFIABLE) with its evidence. Every check is paid, serial-numbered, and provable onchain.
Live: https://cense-lake.vercel.app · Agent ID: ERC-8004 #9853 · Network: Celo mainnet (42220)
Built in the open for Celo's Agents at Work (Aug 28 – Sep 21, 2026). Registered: attribution tag celo_d73bff41d2b6.
- Open https://cense-lake.vercel.app/app
- Paste any factual claim. Press Check · free (the first check is on the house, no wallet).
- A stub comes back in ~10 to 25 seconds: verdict, decisive source, every source used, receipt hash.
- Scroll to /proof: settlements and anchored receipts, read live from the chain.
- Verify any receipt with one RPC call:
curl -X POST https://forno.celo.org -H 'content-type: application/json' \ -d '{"jsonrpc":"2.0","id":1,"method":"eth_getLogs","params":[{"address":"0x2f3e570b31daaad23e8f7a9cb10866db207238a7","fromBlock":"latest","toBlock":"latest"}]}'
| # | Action | What it proves | Cost | Tx |
|---|---|---|---|---|
| 1 | ERC-8004 identity mint | the agent exists onchain: Agent #9853 | 0.036 CELO | 0x4e3c4e18… |
| 2 | ReceiptAnchor deployed, tag in creation calldata | every future receipt is attributable (celo_d73bff41d2b6 decoded by verifyTx) |
0.047 CELO | 0x6f17e443… |
| 3 | 6 verdict receipts anchored | past checks are provable, not narrated | 0.039 CELO | 0x54d4ae95… |
| 4 | Buyer funded (tagged USDC transfer) | the demo payer is distinct from the agent | 0.003 USDC | 0x39b1284d… |
| 5 | First paid settlement | a real x402 payment: buyer → agent, $0.001 USDC inside the token contract | $0.001 | 0x05db1cc8… |
| 6 | Paid-check receipt anchored | the paid verdict is provable | 0.011 CELO | 0xe8cb2d03… |
| 7 | Live house checks | the engine discriminates: VERIFIED (Everest, Nigeria, Pacific, Bitcoin), REFUTED (Great Wall, coffee), UNVERIFIABLE (thin evidence) | house-paid | ledger |
| Contract | Address | Explorer |
|---|---|---|
| ReceiptAnchor (verdict proofs) | 0x2f3e570b31daaad23e8f7a9cb10866db207238a7 |
Celoscan |
| ERC-8004 Identity Registry (Celo's, ours: #9853) | 0x8004A169FB4a3325136EB29fA0ceB6D2e539a432 |
8004scan |
| Agent payTo wallet | 0x2f7c6472d72EfF23E9cF8b13571A74C8389d9A54 |
Celoscan |
| Real | Disclosed |
|---|---|
| Search runs on Gemini 2.5 Flash with native Google Search grounding; sources come from grounding metadata, never invented | Grounding-source URLs are Google redirect links; the domain shown is extracted from the source title |
| Verdicts rendered by gpt-oss-120b via Cencori; strict three-verdict rules; no guessing | When evidence is thin the agent answers UNVERIFIABLE and names what would settle the claim (this is a feature, shown live) |
| The $0.001 payment settles on mainnet inside the USDC contract; the facilitator pays its gas | The settlement gas itself is paid from facilitator credits (20 free at registration); per-settlement after that costs $0.001 + gas at cost |
| The landing-page ledger reads USDC + USDT Transfer logs and Anchored receipts straight from RPC | Free public RPCs cap log-range depth; the ledger walks bounded windows and says so when a read fails |
| The house check runs the exact production engine | House checks are paid by the project, capped (20/day, 2 per visitor), and disclosed in the UI; the wallet path is the real product |
| The landing hero stub is labeled SPECIMEN on the page | The buyer wallet in the settle proof is project-owned (a smoke test, disclosed here); real adoption means distinct external signers |
| The pre-registration identity mint carried no attribution tag | Identity minting is infrastructure, not a leaderboard metric; every transaction after registration carries celo_d73bff41d2b6, verified with verifyTx on the first one |
claim → 402 → sign → settle → search → verdict → stub
Any x402 client pays the endpoint; no account, no API key:
curl -i https://cense-lake.vercel.app/api/v1/check -X POST \ -H 'content-type: application/json' \ -d '{"claim":"The Eiffel Tower opened in 1889"}' # 402 arrives with payment requirements (USDC, eip155:42220, $0.001). # Sign, retry with your x402 client, the verdict is the body.
Engine: one paid check runs two rail hops. Search on Gemini 2.5 Flash with Google Search grounding (own free quota, independent of shared buckets), verdict on gpt-oss-120b via Cencori, with Groq as fallback. Strictness rules: a distorted real event is REFUTED; absence of evidence is UNVERIFIABLE, never a guess; every verdict cites its decisive source.
Next.js 16 · TypeScript · viem · @x402/* against Celo's hosted facilitator (api.x402.celo.org) · @celo/attribution-tags (ERC-8021) · ERC-8004 identity · Google Gemini grounding · Cencori · Groq · Vercel.
bun install cp .env.example .env # keys listed in .env.example bun run dev # the app, http://localhost:3000 bun run spike/server.ts && bun run spike/buyer.ts "some claim" "http://127.0.0.1:8913/v1/check" bun run scripts/qa.ts https://cense-lake.vercel.app # 34-check QA battery
.env.example documents every key: agent + buyer wallets, x402 facilitator key, Groq, Gemini, Cencori.
app/landing, instrument, x402 API route, house-check + ledger routeslib/engine/claim engine: agent, Gemini search, Groq fallback search, verdict judgecontracts/ReceiptAnchor.solscripts/mint-8004, deploy-anchor, anchor, swap, fund-buyer, mint ledger probes,qa.tsspike/the original payment-rail proof, kept as the low-level reference
Live · Leaderboard draft · Notion brief
License: MIT.
built by Raphie for Celo's Agents at Work