# AI Answer Hallucination Entity Checker (Wikidata)

> AI Answer Hallucination Entity Checker (Wikidata) is a paid API for AI agents from api.fadeandco.workers.dev, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-29).

Checks up to 5 capitalised named entities in an AI-generated text against Wikidata to verify their existence, returning found/not-found status, Wikidata IDs, descriptions, and sentences containing years for manual review.

## Facts

- Endpoint: POST https://api.fadeandco.workers.dev/api/agent-intel/hallucination-claim-checker?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/ai-answer-hallucination-entity-checker-wikidata-7a61156e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_LKzmpVTZ5H71CuZzGG2zu

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 ai-answer-hallucination-entity-checker-wikidata-7a61156e -d '<json body>'
```

Example prompt: Can you check this AI-generated paragraph for hallucinated entity names — verify whether the capitalised names actually exist in Wikidata and flag any sentences that mention specific years? Here's the text: 'Albert Einstein received the Nobel Prize in Physics in 1921 for his discovery of the photoelectric effect, later collaborating with Niels Bohr at the Solvay Institute in Geneva.'

## When to prefer this

Choose this endpoint when you need a lightweight, fast existence-check on named entities in an AI-generated text without running a full semantic fact-verification pipeline. It is ideal for post-generation quality gates in LLM pipelines, RAG audits, or chatbot moderation where you want to quickly surface potentially hallucinated proper nouns and flag date-bearing sentences for human review. Prefer this over general web-search fact-checkers when you specifically want structured Wikidata provenance (IDs and descriptions) for each entity.

## Known failure modes

- Text shorter than 10 or longer than 5000 characters returns a validation error
- No capitalised names detected results in an empty entity list
- Wikidata API unavailability causes lookup failure
- Ambiguous or very common capitalised words (e.g. 'The', 'A') may not resolve to meaningful entities
- More than 5 capitalised names causes only the first 5 to be checked
- Non-English entity names may have lower Wikidata match rates

## How this service works

Checks the named entities in an AI answer (up to 5 capitalised names) against Wikidata: each name is marked found or not found, with its Wikidata ID and description, and sentences containing a year are listed for review. It checks that entities exist, not that claims about them are true, so a found entity can still have a wrong fact.

## Output

A JSON object listing each detected named entity with its Wikidata existence status ('found' or 'not found'), its Wikidata ID and short description when found, plus a list of sentences from the input that contain a year for human review. Also includes a timestamp, a count of not-found entities, and a note reminding that existence does not verify factual accuracy of claims.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "text": {
   "type": "string",
   "description": "The model answer to check, 10 to 5000 characters"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "note": "Existence check only: a found entity can still carry a wrong date or fact. Review the sentences with years yourself.",
  "source": "https://www.wikidata.org/w/api.php",
  "entities": [
   {
    "name": "Marie Curie",
    "status": "found",
    "wikidataId": "Q7186",
    "description": "Polish-born French physicist and chemist (1867–1934)"
   },
   {
    "name": "Nobel Prize",
    "status": "found",
    "wikidataId": "Q7191",
    "description": "set of annual international awards, primarily 5 established in 1895 by Alfred Nobel"
   }
  ],
  "checkedAt": "2026-10-23T09:35:21.542Z",
  "notFoundCount": 0,
  "sentencesWithYears": [
   "Marie Curie won the Nobel Prize in 1903.",
   "She later moved to Mars in 1921."
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/ai-answer-hallucination-entity-checker-wikidata-7a61156e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.fadeandco.workers.dev](https://www.zero.xyz/host/api.fadeandco.workers.dev/llms.txt)