# Citation Verifier & Fact-Checker

> Citation Verifier & Fact-Checker is a paid API for AI agents from x402-deployer.x402-deployer.workers.dev, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-13).

Fetches a source URL and uses an LLM to determine whether a given claim is supported, contradicted, or absent in that source, returning a verdict, confidence score, and evidence quote.

## Facts

- Endpoint: POST https://x402-deployer.x402-deployer.workers.dev/citation-verify
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-deployer-x402-deployer-workers-dev-0971408d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ICarz3-NJFoBvws_NJJ2c

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 x402-deployer-x402-deployer-workers-dev-0971408d -d '<json body>'
```

Example prompt: Can you fact-check this for me — does the article at https://example.com/study actually support the claim that 'coffee consumption reduces risk of type 2 diabetes by 25%'? Give me the verdict, your confidence, and the strongest quote from the page.

## When to prefer this

Use this endpoint when you need to verify whether a specific textual claim is actually supported by a given URL — ideal for catching AI hallucinations in cited sources, validating research claims before publishing, or auditing whether references actually back up stated facts. Prefer this over general web search when you already have the source URL and need a structured verdict with confidence.

## Known failure modes

- URL is unreachable or returns non-200 status — fetch fails, no verdict returned
- Page content exceeds 100KB cap — only first 100KB analyzed, claim may be in truncated portion
- Source is behind a paywall or login — content unavailable, verdict likely 'absent'
- Claim is ambiguous or too vague — low confidence score returned
- LLM provider (Venice) downtime — request fails with upstream error
- URL contains no text content (e.g. pure image or PDF) — extraction fails or returns empty

## How this service works

Citation verifier / fact-check against URL / does-this-source-support-this-claim / hallucination detector. Fetches a source URL (HTML stripped, 100KB cap), and asks Venice claude-sonnet-4-6 whether a given claim is supported, contradicted, or absent. Returns verdict, confidence (0-1), and the strongest evidence quote when available.

## Output

Returns a verdict of 'supported', 'contradicted', or 'absent', a confidence score between 0 and 1, and the strongest evidence quote from the fetched page (when available). The page HTML is stripped and capped at 100KB before LLM analysis.

## Request schema (JSON Schema)

```json
{
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "type": "object",
 "properties": {
  "input": {
   "type": "object",
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "type": "string",
     "enum": [
      "POST"
     ]
    },
    "bodyType": {
     "type": "string",
     "enum": [
      "json",
      "form-data",
      "text"
     ]
    },
    "body": {
     "properties": {
      "claim": {
       "type": "string",
       "description": "The claim to verify."
      },
      "source_url": {
       "type": "string",
       "description": "Public http(s) URL of the source to check against. Up to 100KB read."
      }
     },
     "required": [
      "claim",
      "source_url"
     ]
    }
   },
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "claim": {
       "type": "string"
      },
      "source_url": {
       "type": "string"
      },
      "source_chars": {
       "type": "integer"
      },
      "source_bytes_total": {
       "type": "integer"
      },
      "truncated": {
       "type": "boolean"
      },
      "verdict": {
       "type": "string"
      },
      "confidence": {
       "type": "number"
      },
      "evidence_quote": {
       "type": "string"
      },
      "model": {
       "type": "string"
      },
      "source": {
       "type": "string"
      }
     }
    }
   },
   "required": [
    "type"
   ]
  }
 },
 "required": [
  "input"
 ]
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-deployer-x402-deployer-workers-dev-0971408d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-deployer.x402-deployer.workers.dev](https://www.zero.xyz/host/x402-deployer.x402-deployer.workers.dev/llms.txt)