# FactStamp

> FactStamp is a paid API for AI agents from factstamp.agentrails.workers.dev, paid per call via x402, $0.05/call, status unknown (last checked 2026-10-02).

Verifies figures, named entities, citations, and dependencies against dated primary sources, returning a sourced verdict for AI agent fact-checking pipelines.

## Facts

- Endpoint: POST https://factstamp.agentrails.workers.dev/mcp?utm_source=zero.xyz
- Price: $0.05/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/factstamp-c8206315
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ELNlD-R5jQSIb9_PgKSp6

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-c8206315 -d '<json body>'
```

Example prompt: Can you verify that 'Shopify Inc.' is a real registered company and tell me its official jurisdiction and registration status, with a citation to the primary source?

## When to prefer this

Choose FactStamp when you need verified, cited facts about named entities or figures backed by dated primary sources rather than LLM-generated plausible answers. Especially valuable in multi-agent pipelines where one agent's output needs independent verification before being used downstream. Prefer it over web search when authoritative registry-level confirmation (e.g. GLEIF LEI data) is required, or when 'unknown' is an acceptable and important outcome that must be explicitly flagged.

## Known failure modes

- Entity not found in any registry — returns verdict 'unknown', which is a valid and intentional outcome
- Ambiguous entity name matches multiple records — best match returned but confidence may be low
- Registry source temporarily unavailable — HTTP status codes in sources array will reflect errors
- Malformed input body — 400-level error returned
- Payment not completed via x402 protocol — 402 Payment Required before verification proceeds

## How this service works

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

## Output

Returns a JSON object with a verdict field ('found' or 'unknown'), the canonical entity name, a best-match record including LEI ID, jurisdiction, and registration status, the original query string, and an array of sources with licence info and HTTP status codes from the primary-source registries consulted.

## 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": {
  "best": {
   "id": "549300HGQ43STJLLP808",
   "name": "SHOPIFY INC.",
   "source": "gleif",
   "jurisdiction": "CA-ON",
   "registration_status": "ISSUED"
  },
  "query": "Shopify Inc.",
  "sources": [
   {
    "source": "gleif",
    "licence": "CC0 1.0 Universal",
    "http_status": 200
   }
  ],
  "verdict": "found",
  "accepted": 1
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/factstamp-c8206315/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)