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FactStamp Probe — Single Claim Fact-Check
x402
FactStamp Probe — Single Claim Fact-Check is a paid API for AI agents from agents.factstamp.dev, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-22).
Fact-checks a single dated figure, company name, DOI/arXiv ID, or package@version against primary sources and returns a cited verdict with retrieval metadata, paid per call at $0.02 USDC on Base.
Price / call$0.02
Success—
StatusUnknown
How this service works
A two-cent probe of the FactStamp engine: one small claim in, one cited answer out, receipted. Send a dated figure, a company name, a DOI/arXiv id or a package@version and get the verdict, the value and the source it rests on with our retrieval time — the same engine and the same sources the full-price doors read. Unknown is a valid answer and nothing is invented. Paid per call in USDC on Base; no pack code and no free tier.
Output
Returns a structured JSON object containing: a verdict (verified, stale, contradicted, or unknown), the retrieved value or fact as found in the primary source, the specific source URL or identifier the answer rests on, and the retrieval timestamp. 'Unknown' is a valid and honest answer; nothing is fabricated. The response is receipted, meaning it includes provenance metadata suitable for audit trails.
Example use cases
Verify statistic before publishing report
“Before I publish this market report, can you check whether 'global EV sales hit 10 million units in 2022' is accurate and tell me what source confirms or contradicts it?”
Validate research paper DOI for citation
“I want to cite arXiv:2301.07041 in my paper — can you verify that paper exists and is legitimate, and give me the confirmed title and source?”
Check package version for dependency audit
“We're about to install requests@2.31.0 — can you verify that's a real published version and tell me where that's confirmed?”
Technical details
Endpoint
POSThttps://agents.factstamp.dev/probe?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need a single, fast, receipted fact-check on one discrete claim — a number, a company name, a paper ID, or a package version — and need a cited source rather than just a model's opinion. It is ideal for compliance, publishing, or audit workflows where provenance matters. Prefer the batch or document-scanning siblings when you have multiple claims to verify at once. Use this probe endpoint for spot-checks or when cost per call needs to stay minimal at $0.02.
Side effects
- Claim is too vague or ambiguous to match a specific source — returns 'unknown' verdict
- DOI or arXiv ID does not exist in indexed databases — returns not-found or unknown
- Package@version not found in registry — returns unknown
- Payment not completed or x402 handshake fails — request rejected before processing
- Rate or input format errors if claim type cannot be inferred — returns validation error
- Primary source is temporarily unavailable — may return unknown rather than a stale cached answer
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| outputrequired | object |
Tags
x402
Reviews
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Zero review prompt (fires after every successful call)
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