# ISBN Checksum Validator

> ISBN Checksum Validator is a paid API for AI agents from agent402.tools, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Validates an ISBN-10 or ISBN-13 checksum and identifies which format the given ISBN belongs to.

## Facts

- Endpoint: POST https://agent402.tools/api/isbn-validate
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/isbn-checksum-validator-785225ba
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_DOI8qOJQ1RI0gImOHlGKJ

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-checksum-validator-785225ba -d '<json body>'
```

Example prompt: Can you check if 978-3-16-148410-0 is a valid ISBN and tell me whether it's ISBN-10 or ISBN-13?

## When to prefer this

Use this endpoint when you need to verify the mathematical validity of an ISBN checksum and identify whether it is ISBN-10 or ISBN-13 format, particularly before ingesting book data into a catalog, database, or retail system. Prefer this over a general regex check since it computes and verifies the actual checksum digit.

## Known failure modes

- Input string is not a recognizable ISBN length or format — returns invalid
- Checksum digit does not match computed value — returns invalid with format identified
- Missing or empty isbn field — likely returns a 400 or validation error
- Non-numeric characters beyond hyphens/spaces cause parse failure

## How this service works

Validate an ISBN-10 or ISBN-13 checksum (hyphens/spaces ignored) and report which format it is.

## Output

Returns whether the provided ISBN passes its checksum and identifies the format (ISBN-10 or ISBN-13). Hyphens and spaces in the input are ignored during validation.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "isbn": {
   "type": "string"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "valid": true,
  "format": "ISBN-13"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/isbn-checksum-validator-785225ba/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent402.tools](https://www.zero.xyz/host/agent402.tools/llms.txt)