# Claim Verification

> Claim Verification is a paid API for AI agents from x402.agentindex.world, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-30).

Checks whether a given source text supports, contradicts, or gives insufficient information about a factual claim, returning a typed verdict with a probability score.

## Facts

- Endpoint: POST https://x402.agentindex.world/verify?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/claim-verification-8383b564
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_YtpBi9TKjUdqsYxo3Zkmm

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 claim-verification-8383b564 -d '<json body>'
```

Example prompt: Check whether this passage — 'The Eiffel Tower was completed in 1889 and stands 330 meters tall' — supports or contradicts the claim 'The Eiffel Tower is taller than 300 meters', and give me a probability score.

## When to prefer this

Choose this endpoint when you need a structured, probabilistic verdict on whether a specific text passage supports or refutes a claim — not free-form summarization. It is ideal for fact-checking pipelines, RAG validation, citation auditing, or any workflow requiring a machine-readable true/false/inconclusive classification with a confidence score rather than a generated explanation.

## Known failure modes

- Missing 'claim' or 'source' field returns a 400 validation error
- Source text too short or uninformative may result in 'insufficient information' verdict with low confidence
- Payment failure or missing x402 header returns a 402 Payment Required response
- Very long source texts may be truncated or cause timeouts
- Ambiguous or compound claims may yield uncertain probabilities near 0.5

## How this service works

Check whether a source supports, contradicts, or gives insufficient information about a claim - a typed verdict with a real probability, not generated text. Try GET /verify/sample.

## Output

A typed verdict indicating whether the source supports, contradicts, or gives insufficient information about the claim, paired with a real probability score (not free-form generated text).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "claim": {
   "type": "string",
   "description": "The factual claim to check."
  },
  "source": {
   "type": "string",
   "description": "The source text to check the claim against."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "verdict": "supported",
  "confidence": 1,
  "probability": 1,
  "x402_receipt": {
   "upstream": "verification",
   "latency_ms": 390,
   "model_served": "jev",
   "price_paid_usdc": 0
  },
  "probabilities": {
   "supported": 1,
   "contradicted": 0,
   "not_enough_info": 0
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/claim-verification-8383b564/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.agentindex.world](https://www.zero.xyz/host/x402.agentindex.world/llms.txt)