# Wikidata Facts – Identifier Lookup

> Wikidata Facts – Identifier Lookup is a paid API for AI agents from wikidata-facts.x402tookit.com, paid per call via x402, $0.03/call, status unknown (last checked 2026-10-21).

Looks up the Wikidata entity matching a given identifier (ISBN, ORCID, IMDb ID, ISO code, VIAF, GeoNames ID, or DOI) with check-digit validation.

## Facts

- Endpoint: GET https://wikidata-facts.x402tookit.com/identifier-lookup?utm_source=zero.xyz
- Price: $0.03/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/wikidata-facts-identifier-lookup-a4e5852e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_h7fSF00tt3-tdNOyQbis-

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 wikidata-facts-identifier-lookup-a4e5852e
```

Example prompt: Can you look up the Wikidata entity for ISBN 9780141439518 and validate the check digit?

## When to prefer this

Use this endpoint when you have a structured external identifier (ISBN, ORCID, IMDb, ISO code, VIAF, GeoNames, DOI) and need to resolve it to a Wikidata entity with validation. Prefer this over general Wikidata search when the identifier is known, as it provides check-digit validation and a precise 1-to-1 match rather than a fuzzy name search.

## Known failure modes

- Invalid check digit causes validation failure with reasons array populated
- Identifier not found in Wikidata returns empty matches array
- Unsupported identifier type returns an error
- Malformed identifier value (wrong format) causes rejection
- Wikidata service temporarily unavailable may return degraded flag set to true

## How this service works

Find the Wikidata entity for an ISBN, ORCID, IMDb id, ISO code, VIAF, GeoNames id or DOI, with check-digit validation.

## Output

Returns the matched Wikidata entity or entities (Q-id, label, description, URL), validation status of the identifier including check-digit result, the normalised form of the identifier, any reasons for validation failure, and source attribution with an as-of timestamp.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "type",
      "value"
     ],
     "properties": {
      "type": {
       "type": "string",
       "description": "One of: isbn, orcid, imdb, iso-alpha2, iso-alpha3, iso-numeric, iso-4217, iso-639-1, viaf, geonames, doi"
      },
      "value": {
       "type": "string",
       "description": "The identifier, e.g. 9780141439518 or FR or nm0000093"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "type": {
       "type": [
        "null",
        "string"
       ]
      },
      "valid": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "value": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "matches": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "object",
        "properties": {
         "id": {
          "type": [
           "null",
           "string"
          ]
         },
         "url": {
          "type": [
           "null",
           "string"
          ]
         },
         "label": {
          "type": [
           "null",
           "string"
          ]
         },
         "description": {
          "type": [
           "null",
           "string"
          ]
         }
        }
       }
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "property": {
       "type": [
 
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/wikidata-facts-identifier-lookup-a4e5852e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from wikidata-facts.x402tookit.com](https://www.zero.xyz/host/wikidata-facts.x402tookit.com/llms.txt)