# ISBN Check Digit Validator & Converter

> ISBN Check Digit Validator & Converter is a paid API for AI agents from id-validators.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-30).

Validates the check digit of an ISBN-10 or ISBN-13 and converts between the two forms.

## Facts

- Endpoint: GET https://id-validators.x402tookit.com/isbn-check?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/isbn-check-digit-validator-converter-0effacdb
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_fsJ3XKlVXxy_5C9hhUa-M

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 isbn-check-digit-validator-converter-0effacdb
```

Example prompt: Can you check whether the ISBN 978-0-306-40615-7 is valid and tell me its ISBN-10 equivalent?

## When to prefer this

Choose this endpoint when you specifically need to validate the check digit of an ISBN-10 or ISBN-13 and/or convert between the two forms. It is purpose-built for book identifiers and returns detailed per-field breakdown including prefix, form, and normalized representation — more specific than a general barcode validator. Use sibling endpoints for other identifier types (ISSN, EAN, CUSIP, etc.).

## Known failure modes

- Missing or empty 'id' query parameter returns an error
- Malformed input (e.g. non-numeric characters in wrong positions) results in an invalid verdict with reasons
- ISBN of wrong length (not 10 or 13 digits) returns an invalid verdict
- Network or service unavailability returns a non-200 response
- Payment failure (x402) prevents the request from completing

## How this service works

Validate an ISBN-10 or ISBN-13 check digit and convert between the two forms.

## Output

Returns a verdict (valid/invalid), the normalized ISBN, the detected form (ISBN-10 or ISBN-13), the ISBN-10 equivalent if applicable, the publisher prefix, a human-readable summary, and an array of reasons explaining any validation failures. May also include source, asOf timestamp, degraded flag, disclaimer, and a list of checks not performed.

## 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": [
      "id"
     ],
     "properties": {
      "id": {
       "type": "string",
       "description": "The ISBN"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "form": {
       "type": [
        "null",
        "string"
       ]
      },
      "isbn10": {
       "type": [
        "null",
        "string"
       ]
      },
      "prefix": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "normalised": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      }
     }
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/isbn-check-digit-validator-converter-0effacdb/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from id-validators.x402tookit.com](https://www.zero.xyz/host/id-validators.x402tookit.com/llms.txt)