# Web Evidence API – Claim Verification

> Web Evidence API – Claim Verification is a paid API for AI agents from api.aisoup.net, paid per call via x402, $0.05/call, status unknown (last checked 2026-10-13).

Verifies a text claim against web sources, returning a verdict, cited evidence, source snapshots, cryptographic hashes, and conflict detection

## Facts

- Endpoint: POST https://api.aisoup.net/v1/claims/verify?utm_source=zero.xyz
- Price: $0.05/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-1c1e111c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_BXyMp520M7l-ycwE2OfYP

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-1c1e111c -d '<json body>'
```

Example prompt: Can you fact-check this claim for me: 'The global average temperature has risen by 1.1 degrees Celsius since pre-industrial times' — search authoritative sources only, include up to 5 sources, flag any conflicts you find, and tell me what the evidence says?

## When to prefer this

Choose this endpoint when you need cited, verifiable evidence for or against a specific factual claim — especially when you need source snapshots and cryptographic provenance for auditability. Prefer it over general web search when the output must include a structured verdict, conflict detection, and hash-anchored evidence suitable for compliance, journalism, or agent self-verification workflows. Particularly useful when you need jurisdiction-scoped or domain-filtered verification with freshness controls.

## Known failure modes

- Claim is too vague or ambiguous for sources to confirm — returns unconfirmed status with explanation
- Freshness constraint too tight — no sources found within the requested time window
- All candidate domains blocked — returns error if no sources available after filtering
- Claim exceeds 4000 character limit — returns 400 validation error
- Minimum source threshold not met — returns result noting insufficient sources found
- Payment failure via x402/MPP — returns 402 Payment Required
- Rate limiting or upstream web access failure — returns 503 or timeout

## How this service works

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

## Output

Returns a JSON object containing: a verdict status (e.g. confirmed, unconfirmed, contested), a natural-language conclusion, an array of cited evidence items with URLs and excerpts, a list of atomic facts extracted, any conflicting sources, web snapshots with hashes for provenance, a timestamp of when verification was observed, a unique verification ID, provider sources used, and any limitations of the verification.

## 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": 8,
   "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-1c1e111c/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)