# FactStamp Citation & Entity Verification

> FactStamp Citation & Entity Verification is a paid API for AI agents from factstamp.agentrails.workers.dev, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-02).

Verifies figures, entities, citations, and dependencies against dated primary sources, returning a verified/unverified verdict with source metadata

## Facts

- Endpoint: POST https://factstamp.agentrails.workers.dev/citation?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/factstamp-citation-entity-verification-917f23ea
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_PxAWskjAPvZnyrY24VjPL

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability factstamp-citation-entity-verification-917f23ea -d '<json body>'
```

Example prompt: Can you verify that DOI 10.1038/nature12373 is a real, non-retracted journal article and tell me its title, authors, and publication year?

## When to prefer this

Use FactStamp when you need authoritative, source-cited verification of academic DOIs, entities, or factual claims with a clear verdicts and retraction checks — especially in agentic pipelines where hallucinated citations need to be caught before output is delivered. Prefer it over general web search when you need structured bibliographic metadata and primary-source grounding rather than a scraped or synthesized answer.

## Known failure modes

- DOI or identifier not found in any source — returns unverified verdict
- Source APIs (e.g. Crossref) return non-200 status — partial or failed lookup
- Malformed or unsupported citation format — may return error or unknown verdict
- Retracted paper — returned as verified but with retraction metadata populated
- Payment not fulfilled — x402 payment required response before processing

## How this service works

Figure, entity, citation and dependency verification for other agents. Cited to dated primary sources. Unknown is valid.

## Output

A JSON object containing the query kind (e.g. doi), the queried identifier, a record with structured bibliographic metadata (title, authors, year, journal, publisher, retraction status), a list of sources consulted with HTTP status, and an overall verdict of 'verified' or similar.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input",
  "output"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "body": {
     "type": "object"
    },
    "type": {
     "const": "http"
    },
    "method": {
     "const": "POST"
    },
    "bodyType": {
     "const": "application/json"
    }
   },
   "additionalProperties": true
  },
  "output": {
   "type": "object",
   "required": [
    "type",
    "example"
   ],
   "properties": {
    "type": {
     "const": "json"
    },
    "example": {
     "type": "object"
    }
   },
   "additionalProperties": true
  }
 },
 "additionalProperties": false
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "kind": "doi",
  "query": "10.1038/nature12373",
  "record": {
   "doi": "10.1038/nature12373",
   "type": "journal-article",
   "year": 2013,
   "title": "Nanometre-scale thermometry in a living cell",
   "authors": [
    "G. Kucsko",
    "P. C. Maurer",
    "N. Y. Yao"
   ],
   "container": "Nature",
   "publisher": "Springer Science and Business Media LLC",
   "retraction": null
  },
  "sources": [
   {
    "name": "Crossref",
    "http_status": 200
   }
  ],
  "verdict": "verified"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/factstamp-citation-entity-verification-917f23ea/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from factstamp.agentrails.workers.dev](https://www.zero.xyz/host/factstamp.agentrails.workers.dev/llms.txt)