# Fact-Check Claim Against Sources

> Fact-Check Claim Against Sources is a paid API for AI agents from red-breeze-8b8c.keenanbooker83.workers.dev, paid per call via x402, $0.04/call, status unknown (last checked 2026-09-14).

Checks a factual claim against one to three supplied source URLs and returns a verdict on its accuracy

## Facts

- Endpoint: POST https://red-breeze-8b8c.keenanbooker83.workers.dev/fact-check
- Price: $0.04/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fact-check-claim-against-sources-44cf9447
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_wR-OKgmReoW7Hdbwue8tq

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 fact-check-claim-against-sources-44cf9447 -d '<json body>'
```

Example prompt: Can you fact-check this claim — 'Global average temperatures have risen by 1.1°C since pre-industrial times' — against these two sources: https://www.nasa.gov/climate and https://www.ipcc.ch/report/ar6/wg1/?

## When to prefer this

Use this endpoint when you have a specific factual claim and one to three concrete source URLs to check it against. It is distinct from a general web search or source credibility evaluator — it performs targeted claim-vs-source verification rather than open-ended research. Prefer this over the sibling 'verify citation' endpoint when you need a broader fact-check that may draw on multiple sources simultaneously rather than verifying a single exact quotation.

## Known failure modes

- Source URL is inaccessible, paywalled, or returns a non-200 response — endpoint may return an error or incomplete analysis
- Claim is too vague or opinion-based to be fact-checkable — may return an indeterminate verdict
- Source URLs do not contain information relevant to the claim — returns a 'not addressed by sources' result
- Claim text exceeds 4000 characters — request will be rejected with a validation error
- More than three source URLs provided — request will be rejected
- Claim is in a language not supported by the underlying model — may produce inaccurate results

## How this service works

Fact-check a claim against one to three supplied sources

## Output

Returns a structured fact-check verdict indicating whether the supplied claim is supported, partially supported, contradicted, or unverifiable based on the provided source URLs, along with relevant excerpts or reasoning drawn from those sources.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "claim": {
   "type": "string",
   "maxLength": 4000,
   "minLength": 1,
   "description": "Factual claim to check."
  },
  "sourceUrls": {
   "type": "array",
   "items": {
    "type": "string",
    "maxLength": 2048,
    "minLength": 1
   },
   "maxItems": 3,
   "minItems": 1,
   "description": "One to three public source URLs against which the claim is checked."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "agent": "Fact-Checking Agent",
  "verdict": "supported",
  "confidence": 0.99,
  "explanation": "The supplied official sources state that Congress approved the declaration on December 8, 1941.",
  "requestAccepted": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fact-check-claim-against-sources-44cf9447/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from red-breeze-8b8c.keenanbooker83.workers.dev](https://www.zero.xyz/host/red-breeze-8b8c.keenanbooker83.workers.dev/llms.txt)