# Source Claim Proof Verifier

> Source Claim Proof Verifier is a paid API for AI agents from source-claim-proof.mattskowronis.workers.dev, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-14).

Verifies whether a specific public web page currently supports, contradicts, or provides insufficient evidence for a single atomic factual claim.

## Facts

- Endpoint: POST https://source-claim-proof.mattskowronis.workers.dev/v1/verify
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/source-claim-proof-verifier-e9d3dad2
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_FLEY_3MOxdifqyBm6rpyr

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 source-claim-proof-verifier-e9d3dad2 -d '<json body>'
```

Example prompt: Can you check whether this Wikipedia page — https://en.wikipedia.org/wiki/Mount_Everest — actually supports the claim that Mount Everest is 8,849 meters tall?

## When to prefer this

Use this endpoint when you need to verify whether a specific, already-known source URL actually substantiates a single discrete factual claim — especially for citation auditing, misinformation detection, or fact-checking pipelines where the source is already identified. This is not a web search tool; you must provide both the URL and the exact claim. Prefer this over general fact-checkers when provenance matters and you need snippet-level evidence from a specific page.

## Known failure modes

- blocked — the target URL returned a 403 or bot-blocking response, so content could not be read
- unreachable — the target URL timed out or returned a 404/5xx error
- unsupported — the URL points to a PDF, video, or non-parseable content type
- insufficient-evidence — the page loads but contains no content clearly related to the claim
- claim too broad or compound — multi-part claims may get ambiguous verdicts; only atomic claims are supported
- URL exceeds 2048 characters or claim is fewer than 3 characters — returns validation error

## How this service works

Verify whether a supplied public source page currently supports one atomic factual claim. Returns supported, contradicted, or insufficient-evidence plus source snippets, or explicit blocked/unreachable/unsupported states. Not a general fact checker or web search.

## Output

Returns a verdict of 'supported', 'contradicted', or 'insufficient-evidence' indicating whether the source page backs the claim, plus relevant text snippets from the page. May also return explicit states: 'blocked' (page denied access), 'unreachable' (page unavailable), or 'unsupported' (page type cannot be analyzed).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "maxLength": 2048,
   "description": "Public HTTP or HTTPS source page URL to inspect."
  },
  "claim": {
   "type": "string",
   "maxLength": 500,
   "minLength": 3,
   "description": "One atomic factual assertion to check against that source only."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/source-claim-proof-verifier-e9d3dad2/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from source-claim-proof.mattskowronis.workers.dev](https://www.zero.xyz/host/source-claim-proof.mattskowronis.workers.dev/llms.txt)