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 2026-10-27).

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

Price / call$0.1

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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-check?utm_source=zero.xyz

When 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
claimrequired	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

Field	Type	Description
lanerequired	string	Which lane served this check.
claimrequired	string
sourcesrequired	array
verdictrequired	string
cachedAt	string
confidencerequired	number
strictnessrequired	string
attestationrequired	string
costBreakdownrequired	object
imageEvidence	object	Present only when an imageUrl was supplied and vision was available.
free_remaining_today	number	Present only on lane:"free" responses — free checks left today (of 3).

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