# Factstamp Document Fact-Check

> 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.

## Facts

- Endpoint: POST https://agents.factstamp.dev/document?utm_source=zero.xyz
- Price: $0.25/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/factstamp-document-fact-check-78a5f435
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_1moPKZeAD1xgWfNxGM9TJ

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-78a5f435 -d '<json body>'
```

Example prompt: Fact-check this report for me — it quotes GDP figures, names several biotech companies, and cites a few academic papers. I need a signed verification bundle with a verdict and receipt for each claim, and I want to know which claims came back verified, stale, contradicted, or unknown.

## When to prefer this

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.

## Known failure modes

- 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

## 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.

## 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
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/factstamp-document-fact-check-78a5f435/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agents.factstamp.dev](https://www.zero.xyz/host/agents.factstamp.dev/llms.txt)