# three.ws Fact-Check API

> three.ws Fact-Check API is a paid API for AI agents from three.ws, paid per call via x402, $0.1/call, status unknown (last checked 2026-09-15).

Verifies a textual claim against live web sources and returns a verdict, confidence score, supporting excerpts, and a cryptographic attestation.

## Facts

- Endpoint: POST https://three.ws/api/x402/fact-check
- Price: $0.1/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/three-ws-fact-check-api-4ae8edee
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_bBAC21a1VxsEQve6Bj9I1

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 three-ws-fact-check-api-4ae8edee -d '<json body>'
```

Example prompt: Can you fact-check this claim for me using high strictness: 'The Eiffel Tower is 330 meters tall'? I want to know the verdict, confidence score, and which sources support or contradict it.

## When to prefer this

Choose this endpoint when you need a verifiable, source-backed verdict on a specific factual claim, especially when you need a cryptographic attestation for auditability. Prefer it over general web search when you want a structured true/false/contradicted/unverifiable verdict with confidence scoring and per-source stance attribution rather than raw search results.

## Known failure modes

- Claim is too vague or ambiguous for web sources to resolve — low confidence verdict returned
- No relevant sources found — verdict may be 'unverifiable'
- Payment of 0.1 USDC not provided or rejected — 402 Payment Required response
- LLM or search backend unavailable — 5xx error
- Claim contains harmful or disallowed content — request rejected
- Attestation generation failure — partial result without cryptographic proof

## How this service works

Make a 3D AI agent from a selfie in 60 seconds. Drop one HTML tag to embed it on any website. Agents think on IBM watsonx.ai (Granite); optionally charge per chat with built-in micropayments.

## Output

Returns a JSON object with the original claim, a verdict (e.g. 'supported', 'contradicted', 'unverifiable'), a confidence score (0-1), a list of web sources each with URL, title, stance, weight, and excerpt, a cryptographic SHA-256 attestation of the result, and a cost breakdown showing LLM tokens used, search calls made, and total USDC spent.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "claim": {
   "type": "string",
   "maxLength": 1000,
   "minLength": 5,
   "description": "The factual claim to verify."
  },
  "imageUrl": {
   "type": "string",
   "format": "uri",
   "maxLength": 2048,
   "description": "Optional http(s) image attached as evidence (a chart, screenshot, label, or photo). A vision model describes it, transcribes any visible text, and weighs its stance toward the claim alongside web sources. Ignored if vision is unavailable."
  },
  "strictness": {
   "enum": [
    "high",
    "medium",
    "low"
   ],
   "type": "string",
   "default": "medium",
   "description": "high: penalizes low-authority sources. medium: default. low: accepts all sources equally."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "lane": "paid",
  "claim": "The Eiffel Tower is 330 meters tall.",
  "sources": [
   {
    "url": "https://en.wikipedia.org/wiki/Eiffel_Tower",
    "title": "Eiffel Tower - Wikipedia",
    "stance": "supports",
    "weight": 0.7,
    "excerpt": "The tower is 330 m (1,083 ft) tall, including a 24 m (79 ft) antenna.",
    "retrievedAt": "2026-05-27T00:00:00.000Z"
   }
  ],
  "verdict": "contradicted",
  "confidence": 0.78,
  "strictness": "high",
  "attestation": "sha256:abcdef1234567890...",
  "costBreakdown": {
   "llmTokens": 1420,
   "totalUsdc": "0.100355",
   "searchCalls": 3
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/three-ws-fact-check-api-4ae8edee/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from three.ws](https://www.zero.xyz/host/three.ws/llms.txt)