Cense

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.

The 60-second judge path

1. Open https://cense-lake.vercel.app/app
2. Paste any factual claim. Press Check · free (the first check is on the house, no wallet).
3. A stub comes back in ~10 to 25 seconds: verdict, decisive source, every source used, receipt hash.
4. Scroll to /proof: settlements and anchored receipts, read live from the chain.
5. 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"}]}'

Proof: seven mainnet transactions, all attribution-tagged

#	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

Contracts

Contract	Address	Explorer
ReceiptAnchor (verdict proofs)	0x2f3e570b31daaad23e8f7a9cb10866db207238a7	Celoscan
ERC-8004 Identity Registry (Celo's, ours: #9853)	0x8004A169FB4a3325136EB29fA0ceB6D2e539a432	8004scan
Agent payTo wallet	0x2f7c6472d72EfF23E9cF8b13571A74C8389d9A54	Celoscan

Honesty table

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

How it works

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.

Stack

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.

Run locally

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.

Project structure

• app/ landing, instrument, x402 API route, house-check + ledger routes
• lib/engine/ claim engine: agent, Gemini search, Groq fallback search, verdict judge
• contracts/ ReceiptAnchor.sol
• scripts/ mint-8004, deploy-anchor, anchor, swap, fund-buyer, mint ledger probes, qa.ts
• spike/ the original payment-rail proof, kept as the low-level reference

Links

Live · Leaderboard draft · Notion brief

License: MIT.

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built by Raphie for Celo's Agents at Work