# FactStamp Document Fact-Check

> FactStamp Document Fact-Check is a paid API for AI agents from factstamp.agentrails.workers.dev, paid per call via x402, $0.25/call, status unknown (last checked 2026-10-15).

Verifies all checkable claims in a submitted document against dated primary sources, returning per-claim verdicts and a signed bundle with receipts.

## Facts

- Endpoint: POST https://factstamp.agentrails.workers.dev/document?utm_source=zero.xyz
- Price: $0.25/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/factstamp-document-fact-check-b2b6a3ac
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_IcxM1Fsq_3D0CjWc9VUKF

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-document-fact-check-b2b6a3ac -d '<json body>'
```

Example prompt: Before I publish this quarterly report, can you run it through FactStamp to verify every figure, company name, and cited paper — I need back a signed bundle with a per-claim verdict and receipt so I know exactly what's confirmed, what's stale, and what couldn't be answered?

## When to prefer this

Choose this endpoint when you need to fact-check an entire document in a single round trip rather than checking individual claims one at a time. It is ideal before publishing, filing, or distributing any document that contains figures, named companies, or cited papers, and when you need a cryptographically signed bundle as an audit trail. Prefer this over per-claim or per-entity endpoints when the document contains mixed claim types (figures, entities, citations) and you want consolidated verification with a single signed receipt.

## Known failure modes

- Document text missing or malformed — returns 400 error
- Payment not attached or insufficient — returns 402 requiring x402 payment
- Primary sources temporarily unreachable — affected claims returned as unknown (not charged)
- Document too large — may be rejected or truncated
- No checkable claims found — returns empty claims array with zero charged credits

## How this service works

Call it before you send, file or publish 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.

## Output

Returns a JSON object containing an array of claims with their kind (figure, entity, etc.), as-of date, source, and verdict (verified, stale, contradicted, or unknown); a signed EdDSA receipt bundle; counts of claims found, answered, unknown, and charged; and a SHA-256 hash of the submitted document. Unknown claims are named but not charged.

## 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": {
  "claims": [
   {
    "kind": "figure",
    "as_of": "2026-08-01",
    "claim": "The RBA cash rate was 4.35% as at August 2026",
    "source": "Reserve Bank of Australia",
    "verdict": "contradicted"
   },
   {
    "kind": "entity",
    "as_of": "2026-10-06",
    "claim": "Shopify Inc. is registered in Canada",
    "source": "GLEIF",
    "verdict": "verified"
   }
  ],
  "receipt": "eyJhbGciOiJFZERTQSJ9…",
  "unknown": 1,
  "answered": 2,
  "claims_found": 3,
  "charged_credits": 2,
  "document_sha256": "9f2c…"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/factstamp-document-fact-check-b2b6a3ac/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)