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three.ws Fact-Check API
x402
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.
Price / call$0.1
Success—
StatusUnknown
How this service works
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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.
Example use cases
Verify customer testimonial authenticity
“I need you to fact-check this customer review claim: 'Our product reduced processing time by 80% for enterprise clients.' Can you tell me if this is supported by our case studies or third-party reports, and give me a confidence score?”
Check social media claim before sharing
“Before I repost this, can you verify if it's true? The claim is: 'Electric vehicles produce 50% fewer emissions than gas cars over their lifetime.' I need the verdict, confidence, and sources that back it up or contradict it.”
Validate financial advisor recommendation
“A financial advisor told me that 'Gold prices have increased 300% over the last decade.' Can you fact-check this with current data and give me a confidence score plus the sources you find?”
Technical details
Endpoint
POSThttps://three.ws/api/x402/fact-checkWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| claim | string | The factual claim to verify. |
| imageUrl | string | 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 | string | high: penalizes low-authority sources. medium: default. low: accepts all sources equally. |
Output
Schema · Response
{
"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
}
}
}Tags
x402
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