# Agent Evidence API – Claim Verification with Cited Web Sources

> Agent Evidence API – Claim Verification with Cited Web Sources is a paid API for AI agents from agent-evidence-api.thx93.workers.dev, paid per call via x402, $0.03/call, status down (last checked 2026-10-15).

Verifies a claim against up to 5 provided URLs, returning excerpts from those pages that support, contradict, or fail to settle the claim, each with a source URL, retrieval timestamp, and content hash.

## Facts

- Endpoint: POST https://agent-evidence-api.thx93.workers.dev/mcp?utm_source=zero.xyz
- Price: $0.03/call
- Payment: x402
- Status: down
- Last checked: 2026-10-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-evidence-api-claim-verification-with-cited-web-sources-8f39b20a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_D9Hue3gHjD6qsBQP0IjaR

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 agent-evidence-api-claim-verification-with-cited-web-sources-8f39b20a -d '<json body>'
```

Example prompt: Can you verify the claim 'mRNA vaccines do not alter human DNA' against these three URLs: https://www.cdc.gov/vaccines/covid-19/index.html, https://www.who.int/news-room/qa-detail/coronavirus-disease-(covid-19)-vaccines, and https://www.nature.com/articles/d41586-021-02483-w — and tell me which passages support, contradict, or fail to settle it, with citations?

## When to prefer this

Choose this endpoint when an agent needs to verify a specific factual claim against authoritative or user-supplied URLs with full citation provenance (source URL, retrieval time, content hash). It is ideal for fact-checking workflows, compliance checks, research validation, or any scenario where the agent must justify its verdict with traceable evidence rather than relying on its own training knowledge. Prefer it over a general web search API when you already have candidate source URLs and need passage-level citation rather than a ranked list of links.

## Known failure modes

- URL is inaccessible, paywalled, or returns a non-200 response — no content retrieved for that source
- Claim is too ambiguous for passages to be classified as supporting or contradicting — returned as inconclusive
- All provided URLs fail to return content — no charge incurred but no evidence returned
- Rate limiting or network timeouts on external URL fetches — partial results or empty response
- Malformed input schema or missing required fields — request rejected with validation error
- URL content has no textual overlap with the claim — all passages returned as inconclusive

## How this service works

Verify a claim against public web sources: send a question and up to 5 URLs, get cited evidence - passages that support, contradict or fail to settle it. Claim verification with a citation for every excerpt: source URL, retrieval time, content hash. Never charges when nothing is retrieved.

## Output

The agent receives a structured response containing excerpts (passages) from the retrieved web pages, each labeled as supporting, contradicting, or inconclusive with respect to the claim. Every passage includes its source URL, the time it was retrieved, and a content hash for integrity verification. If no content is retrieved from any URL, no charge is incurred and an appropriate empty or error response is returned.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "toolName",
    "inputSchema"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "mcp"
    },
    "example": {
     "type": "object"
    },
    "toolName": {
     "type": "string"
    },
    "transport": {
     "enum": [
      "streamable-http"
     ],
     "type": "string"
    },
    "description": {
     "type": "string"
    },
    "inputSchema": {
     "type": "object"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent-evidence-api-claim-verification-with-cited-web-sources-8f39b20a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent-evidence-api.thx93.workers.dev](https://www.zero.xyz/host/agent-evidence-api.thx93.workers.dev/llms.txt)