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Factstamp Citation Verifier
x402
Factstamp Citation Verifier is a paid API for AI agents from agents.factstamp.dev, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-21).
Verifies whether an academic citation (DOI, arXiv ID, or paper title) exists, is retracted, or cannot be found, and returns structured metadata about the work.
Price / call$0.02
Success—
StatusUnknown
How this service works
Says whether a citation can be repeated. Give a DOI, an arXiv ID or a paper title; the answer says whether the work exists, what it is (title, authors, year, container) and whether it has been retracted. A title that is absent from both Crossref and arXiv returns not_found, and a near title match is never reported as verified. Cited to the source record with its retrieval time. Verdicts: verified, ambiguous, retracted, not_found, unknown.
Output
A JSON object containing a verdict (one of: verified, ambiguous, retracted, not_found, unknown), along with structured metadata about the work — title, authors, publication year, container/journal name — and a reference to the source record with its retrieval timestamp.
Example use cases
Retraction check before submission
“I'm about to submit a paper and I want to make sure none of my references have been retracted. Start with this one: DOI 10.1016/j.cell.2011.10.001 — does it exist, and has it been pulled?”
Validate AI-generated citation
“My AI assistant gave me a citation — 'The impact of mRNA vaccines on T-cell immunity' by Zhang et al., 2021 — can you check if that paper actually exists in Crossref or arXiv, or if it's hallucinated?”
arXiv preprint verification
“Check if arXiv:2103.00020 is a real paper, and tell me the title, authors, and year — I need to know it's legitimate before I cite it in my report.”
Technical details
Endpoint
POSThttps://agents.factstamp.dev/citation?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need to verify the existence and integrity of a single academic citation — especially when checking for retracted papers, validating AI-generated references, or confirming a DOI/arXiv ID before publishing or citing. It is superior to a generic web search because it checks authoritative sources (Crossref, arXiv) directly and explicitly flags retractions with a structured verdict.
Side effects
- Title not found in Crossref or arXiv returns verdict 'not_found'
- Near-match titles are never returned as 'verified' — preventing false positives on similar but distinct papers
- Ambiguous cases (e.g. multiple works matching) return verdict 'ambiguous'
- Unknown errors or service unavailability return verdict 'unknown'
- Malformed DOI or arXiv ID may result in not_found or unknown verdict
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| outputrequired | object |
Tags
x402
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