# Web Evidence API – Claim Verification with Cited Sources

> Web Evidence API – Claim Verification with Cited Sources is a paid API for AI agents from api.aisoup.net, paid per call via x402, $0.25/call, status unknown (last checked 2026-10-13).

Verifies a natural-language claim against web sources, returning a verdict, cited evidence, source snapshots, and cryptographic provenance hashes

## Facts

- Endpoint: POST https://api.aisoup.net/v1/claims/verify/research?utm_source=zero.xyz
- Price: $0.25/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/web-evidence-api-claim-verification-with-cited-sources-ad5d2259
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ec4kR_LGIi0RxyWZ0TAkI

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 web-evidence-api-claim-verification-with-cited-sources-ad5d2259 -d '<json body>'
```

Example prompt: Can you verify the claim that 'The Eiffel Tower is 330 meters tall including its antenna' using only authoritative sources, pull at least 2 sources, and include any conflicting information you find?

## When to prefer this

Choose this endpoint when you need verifiable, cited, source-backed fact-checking with cryptographic provenance rather than a simple LLM opinion. It is especially valuable when jurisdiction-specific, freshness-constrained, or domain-restricted evidence is required, or when you need conflict detection across sources. Prefer it over generic web search when the output must be auditable and traceable with snapshot hashes.

## Known failure modes

- Claim text too short (< 3 chars) or too long (> 4000 chars) returns validation error
- Insufficient sources found matching policy returns uncertain status with limitations noted
- Blocked or restricted domains prevent sourcing, reducing evidence quality
- freshnessHours constraint too tight may yield no qualifying sources
- Payment failure via x402/MPP returns 402 before research begins
- Ambiguous claims without enough context may return low-confidence or inconclusive results

## How this service works

Machine-discoverable services AI agents can call and purchase autonomously.

## Output

A JSON object containing: a verdict status (e.g. confirmed, refuted, uncertain), a natural-language conclusion, an array of evidence citations with URLs and excerpts, conflicting source entries, web snapshots with hashes for provenance, atomic facts extracted from sources, a unique verificationId, a timestamp of observation, and any noted limitations of the research.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "asOf": {
   "type": [
    "string",
    "null"
   ],
   "format": "date",
   "description": "Optional date at which the claim should be evaluated."
  },
  "claim": {
   "type": "string",
   "maxLength": 4000,
   "minLength": 3,
   "description": "The factual claim to verify."
  },
  "language": {
   "type": "string",
   "description": "Preferred response language or auto."
  },
  "maxSources": {
   "type": "integer",
   "maximum": 20,
   "minimum": 1,
   "description": "Maximum number of evidence sources to return."
  },
  "jurisdiction": {
   "type": [
    "string",
    "null"
   ],
   "description": "Optional country, state, or legal jurisdiction."
  },
  "sourcePolicy": {
   "enum": [
    "official_only",
    "authoritative",
    "open_web"
   ],
   "description": "Policy controlling which kinds of web sources may be used."
  },
  "allowedDomains": {
   "type": "array",
   "items": {
    "type": "string"
   },
   "description": "Optional hostname allowlist without schemes or paths."
  },
  "blockedDomains": {
   "type": "array",
   "items": {
    "type": "string"
   },
   "description": "Optional hostname blocklist without schemes or paths."
  },
  "freshnessHours": {
   "type": [
    "integer",
    "null"
   ],
   "maximum": 8760,
   "minimum": 1,
   "description": "Maximum preferred source age in hours."
  },
  "minimumSources": {
   "type": "integer",
   "maximum": 10,
   "minimum": 1,
   "description": "Minimum number of evidence sources requested."
  },
  "includeConflicts": {
   "type": "boolean",
   "description": "Whether to search for and report conflicting evidence."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "claim": "The Base mainnet chain ID is 8453.",
  "status": "confirmed",
  "evidence": [],
  "conflicts": [],
  "snapshots": [],
  "conclusion": "Authoritative sources confirm that Base mainnet uses chain ID 8453.",
  "observedAt": "2026-01-01T00:00:00Z",
  "provenance": {},
  "atomicFacts": [],
  "limitations": [],
  "verificationId": "cv_example",
  "providerSources": []
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/web-evidence-api-claim-verification-with-cited-sources-ad5d2259/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.aisoup.net](https://www.zero.xyz/host/api.aisoup.net/llms.txt)