# AsterPay Fact-Check API

> AsterPay Fact-Check API is a paid API for AI agents from x402.asterpay.io, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Verifies factual claims against sources using an LLM, returning a verdict, evidence, confidence score, and summary

## Facts

- Endpoint: POST https://x402.asterpay.io/v2/x402/ai/fact-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/asterpay-fact-check-api-84be299a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_lO-oHzNt4QjkZ75WICgYE

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 asterpay-fact-check-api-84be299a -d '<json body>'
```

Example prompt: Can you fact-check this claim for me: 'Apple reported $94.9B in revenue last quarter' — I need to know if it's supported, contradicted, or unverifiable, and how confident you are?

## When to prefer this

Choose this endpoint when an AI agent needs to verify a specific factual claim (e.g. a revenue figure, a statistic, a quoted fact) against real sources, and requires a structured verdict with evidence and confidence. Prefer over generic LLM prompting when you need a structured, auditable fact-check response with a clear verdict enum and supporting evidence, especially in agentic pipelines requiring trustworthy, verifiable outputs.

## Known failure modes

- Claim is too vague or ambiguous to verify — low confidence score returned
- Source data unavailable or outdated — verdict may be 'unverifiable'
- Rate limit exceeded — 402 or 429 response
- Malformed request body — 400 error
- Payment not accepted or insufficient USDC — 402 payment required error

## How this service works

Source-bounded fact-check. Verify a claim against provided source text. Returns verdict: supported, contradicted, or unverifiable. Does NOT search the web.

## Output

Returns a JSON object with: verdict (e.g. 'contradicted', 'supported', 'unverifiable'), a plain-English summary, the evidence used to reach the verdict, a confidence score (0–1), the LLM model used, latency in milliseconds, and the number of claims checked.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "claim": {
   "type": "string"
  },
  "source": {
   "type": "string"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "model": "llama-3.3-70b-versatile",
  "summary": "Revenue figure directly contradicted by source.",
  "verdict": "contradicted",
  "evidence": "Source states $119.6B, not $94.9B as claimed.",
  "confidence": 0.98,
  "latency_ms": 820,
  "claims_checked": 1
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/asterpay-fact-check-api-84be299a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.asterpay.io](https://www.zero.xyz/host/x402.asterpay.io/llms.txt)