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ClaimGate: A Fact-Check Endpoint for AI Agents — $0.25 USDC per Claim, Quote-Verified Evidence, Coherence-Gated Verdict

#mcp #x402 #ai #web3

ClaimGate: A Fact-Check Endpoint for AI Agents — $0.25 USDC per Claim, Quote-Verified Evidence, Coherence-Gated Verdict

AI agents repeat claims they cannot verify. ScriptMasterLabs already checks whether engines cite a source (CiteGate) and whether package docs match reality (ScriptDocs) — but nothing in the fleet took an arbitrary claim and fact-checked it against the live web. ClaimGate closes that gap, live today.

The call: fact_check_claim over MCP (POST https://scriptmasterlabs.com/claimgate/mcp) or plain HTTP (POST https://claimgate.onrender.com/fact-check). Price: 0.25 USDC per fact check, settled on Base (eip155:8453) via x402 to 0xc29185fa176357612f3194735753e520e91adc46. No subscription, no account, no API key.

How a check runs

  1. The claim is decomposed into atomic sub-claims.
  2. Sources are fetched live server-side (caller-supplied URLs, or ClaimGate's own bounded web search). Every source is recorded with fetch status and a SHA-256 content hash; blocked or failed fetches are reported, never treated as evidence.
  3. Sources are grouped into independent families — syndicated copies of one story are one family; pages on one domain are one family.
  4. A Jev juror (jev-1.13.0) judges each family: supports (+1), contradicts (−1), or does-not-address (0) — and must cite an exact quote from the fetched text.
  5. Anti-hallucination gate: the server whitespace-normalizes and verifies every quote literally exists in that source's fetched text. A quote that fails is discarded and counted in the receipt; a family whose quotes all fail casts no vote.
  6. Coherence gate: families are weighted by source class (primary/official 3, reputable secondary 2, other 1). coherence = |Σ w·d| / Σ w over addressing families. SUPPORTED requires coherence ≥ 0.80, a positive net direction, and ≥ 2 independent addressing families. CONTRADICTED mirrors it. 0.50–0.79 is MIXED. Anything else is UNVERIFIABLE — the gate never guesses.
  7. The verdict is sealed as a receipt (SQLite on a persistent disk) and returned with the settlement transaction. Receipts are re-fetchable free, forever, via fact_check_receipt or GET /receipts/<id>.

Free tools ride along: fact_check_preview (fetch plan, no verdict), fact_check_status, fact_check_methodology, fact_check_receipt.

Launch-day proof (SELF-PROOF)

Three checks run from the owner's proof wallet on 2026-10-30 — real on-chain settlements, published with receipt ids so anyone can re-fetch the full evidence packs:

Claim Verdict Coherence Receipt Settlement
"ScriptMasterLabs' Verdict Protocol charges $0.25 per decision on Base." SUPPORTED 0.857 (6 of 7 weighted families; 4 verbatim quotes validated) cg_mvuzfnux_b4319b13 0x6e5b9306…
"ScriptMasterLabs is a subsidiary of Coinbase." UNVERIFIABLE (never SUPPORTED — sources address SML, not Coinbase ownership; jurors returned does-not-address instead of inventing a contradiction) 0 cg_mvuzg2fz_0e065c86 0xb1029d5f…
An invented private detail with no web footprint UNVERIFIABLE 0 cg_mvuzgd0j_d9877db4 0xa65a021d…

Receipt persistence was proven the same day: the SUPPORTED receipt was re-fetched byte-identical after a full service redeploy.

Honest limits: verdicts are labeled calibrated: false — the thresholds are stated and fixed, but the jury has not been benchmarked against a labeled fact-check corpus. An UNVERIFIABLE verdict means the public web did not settle the question, not that the claim is false.

Full pricing, methodology and the proof table: https://scriptmasterlabs.com/claimgate — the x402 discovery document lives at https://claimgate.onrender.com/.well-known/x402

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