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Factstamp Document Fact-Check
x402
Factstamp Document Fact-Check is a paid API for AI agents from agents.factstamp.dev, paid per call via x402, $0.25/call, status unknown (last checked 2026-10-21).
Verifies every checkable claim in a prose document against dated primary sources, returning a signed bundle with per-claim verdicts and licence receipts.
Price / call$0.25
Success—
StatusUnknown
How this service works
For a document that quotes figures, names companies or cites papers: post the text and every checkable claim comes back verified against dated primary sources, as one signed bundle with a per-claim receipt and its licence. Claims we cannot answer are named and never charged, and the preview is free. Verdicts: verified, stale, contradicted, unknown. Prose, not a list: a bare bibliography belongs to /bulk.
Output
A signed verification bundle covering every checkable claim in the submitted document. Each claim receives a verdict (verified, stale, contradicted, or unknown), a dated primary-source citation, a licence for use, and a per-claim receipt. Claims that cannot be answered are named explicitly and not charged. The response is returned as structured prose rather than a bare list.
Example use cases
Pre-publication article fact-check
“Before we publish this investigative piece, fact-check it against primary sources — it cites unemployment figures from the BLS, names three pharmaceutical companies, and references a 2022 Nature paper. Give me a verdict for each claim and flag anything that's stale or contradicted.”
Investor report accuracy review
“Our investment memo references market size statistics, revenue figures for four companies, and a McKinsey study. Can you verify all those claims against their original sources and send back a signed bundle I can attach to the filing?”
Academic whitepaper verification
“I need to verify all the checkable facts in this whitepaper before submission — it cites inflation data, references WHO statistics, and names several biotech firms. I want a per-claim receipt showing what's verified, what's stale, and what you couldn't confirm.”
Technical details
Endpoint
POSThttps://agents.factstamp.dev/document?utm_source=zero.xyzWhen to prefer
Use this endpoint when you have a full prose document containing multiple heterogeneous claims — figures, company names, citations — and need a holistic, signed verification bundle with per-claim receipts in a single call. Prefer this over the /bulk endpoint when your content is narrative prose rather than a bibliography or dependency manifest. Choose this over the single-stat or single-citation endpoints when you need comprehensive coverage of an entire document rather than targeted checks on individual claims.
Side effects
- Document text missing or malformed — 400 error indicating required body
- No checkable claims detected in the document — returns empty or unknown verdicts
- Primary source unavailable or unreachable — claim marked 'unknown' and not charged
- Payment not provided or insufficient — 402 Payment Required before processing
- Rate limiting or server overload — 429 or 503 response
- Document too large for single-call processing — may require chunking or /bulk endpoint
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| outputrequired | object |
Tags
x402
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