# Claim Check

> Claim Check is a paid API for AI agents from claim-check.agent-utils.workers.dev, paid per call via x402, $0.05/call, status unknown (last checked 2026-09-15).

Fact-checks a claim against a source document or URL with verbatim quote grounding, returning a verdict, confidence score, and supporting excerpts.

## Facts

- Endpoint: POST https://claim-check.agent-utils.workers.dev/v1/claim-check
- Price: $0.05/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/claim-check-cdfa4dcb
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_mXHcxdVWx4rQv5yXHGNkN

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-check-cdfa4dcb -d '<json body>'
```

Example prompt: Can you fact-check the claim 'The Eiffel Tower is 330 metres tall' against https://en.wikipedia.org/wiki/Eiffel_Tower and give me the verdict, confidence, and any verbatim quotes from the page that support or contradict it?

## When to prefer this

Choose this endpoint when you need grounded, quote-backed fact verification rather than open-ended LLM opinion — it discards any model-generated quote not found verbatim in the source, making results auditable. Prefer it over generic LLM calls when you need a structured verdict enum and confidence score for downstream logic, or when you need to extract typed structured data from invoices, receipts, or job postings without building a custom extraction prompt. It is particularly valuable when source provenance and citation traceability matter.

## Known failure modes

- Source URL is unreachable or returns non-200 — fetch fails and an error is returned
- Source text exceeds 200,000 characters — truncated or rejected
- Claim is ambiguous — verdict returned as 'unclear' with low confidence
- Model quota exhausted for the day — 402 or quota error from /health endpoint
- Verbatim quotes hallucinated by model are discarded (droppedQuotes > 0), reducing grounded evidence
- Payment not included or invalid — x402 payment required error

## How this service works

Grounded verification and extraction for AI agents: fact-check a claim against a source with verbatim quotes, or turn invoices, receipts, job posts and any text into typed JSON. Pay per call over x402, no API key. Daily model quota published at /health.

## Output

A JSON object containing: the original claim, a verdict (supported/contradicted/not_found/unclear), a confidence score between 0 and 1, an array of verbatim quotes from the source that ground the verdict, a plain-language explanation, the source URL if provided, character count of the source, count of grounded vs dropped quotes, and the model name used.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "claim"
     ],
     "properties": {
      "claim": {
       "type": "string",
       "maxLength": 2000,
       "description": "The statement to verify"
      },
      "source": {
       "type": "string",
       "maxLength": 200000,
       "description": "Source text (use this or sourceUrl)"
      },
      "sourceUrl": {
       "type": "string",
       "description": "Public http(s) URL; its readable text becomes the source (max 2 MB page)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "claim": {
       "type": "string"
      },
      "model": {
       "type": "string"
      },
      "quotes": {
       "type": "array",
       "items": {
        "type": "string"
       },
       "description": "Verbatim excerpts verified to appear in the source"
      },
      "modelMs": {
       "type": "integer"
      },
      "verdict": {
       "enum": [
        "supported",
        "contradicted",
        "not_found",
        "unclear"
       ],
       "type": "string"
      },
      "sourceUrl": {
       "type": [
        "string",
        "null"
       ]
      },
      "confidence": {
       "type": "number",
       "maximum": 1,
       "minimum": 0
      },
      "explanation": {
       "type": "string"
      },
      "sourceChars": {
       "type": "integer"
      },
      "droppedQuotes": {
       "type": "integer",
       "description": "Model quotes discarded because they were not found verbatim in the source"
      },
      "groundedQuotes": {
       "type": "integer"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "claim": "The Eiffel Tower is 330 metres tall.",
  "model": "@cf/meta/llama-3.3-70b-instruct-fp8-fast",
  "quotes": [
   "The tower is 330 metres (1,083 ft) tall"
  ],
  "modelMs": 1800,
  "verdict": "supported",
  "sourceUrl": "https://en.wikipedia.org/wiki/Eiffel_Tower",
  "confidence": 0.95,
  "explanation": "The source states the tower's height as 330 metres.",
  "sourceChars": 24000,
  "droppedQuotes": 0,
  "groundedQuotes": 1
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/claim-check-cdfa4dcb/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from claim-check.agent-utils.workers.dev](https://www.zero.xyz/host/claim-check.agent-utils.workers.dev/llms.txt)