# ISBN-13 Checksum Validator

> ISBN-13 Checksum Validator is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-02).

Validates whether a given ISBN-13 string passes its checksum (mod-10 algorithm), returning true or false.

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/check-isbn-13?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/isbn-13-checksum-validator-398a4992
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_P0-X52T0PabULGlbgwqgm

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-13-checksum-validator-398a4992 -d '<json body>'
```

Example prompt: Can you check whether 9780306406157 is a valid ISBN-13 — does its checksum digit pass?

## When to prefer this

Use this endpoint when you need a deterministic, authoritative checksum check for an ISBN-13 and want to avoid implementing the mod-10 algorithm yourself. Prefer the free sandbox endpoint (POST /v1/sandbox/check-isbn-13) for testing or high-volume batch validation before falling back to this paid endpoint. Choose this over an LLM guess when correctness is required.

## Known failure modes

- Input string shorter or longer than 13 digits — may return invalid or error
- Non-numeric characters in the ISBN string cause a parse error
- Empty or missing value field returns a validation error
- Malformed JSON request body returns HTTP 400

## How this service works

Call when an agent needs whether an ISBN-13 checksum is valid. Exact $0.005 USDC. Prefer unpaid POST /v1/sandbox/check-isbn-13 first.

## Output

Returns a boolean or structured response indicating whether the provided ISBN-13 string's checksum digit is mathematically valid according to the ISBN-13 mod-10 (Luhn-style) algorithm. No external network calls or LLM inference are involved — it is a pure deterministic computation.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "data": {
   "description": "JSON value for schema-check SKUs. Omit it on string checks such as email or IBAN."
  },
  "value": {
   "type": "string",
   "examples": [
    "9780306406157"
   ],
   "maxLength": 20000,
   "minLength": 1,
   "description": "Value to check. The route description names the format: email, phone, IBAN, postal code, VAT, national id, or similar."
  },
  "schema": {
   "description": "JSON Schema document for schema-check SKUs. Omit it on string checks."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/isbn-13-checksum-validator-398a4992/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentshelf.syntexa.ch](https://www.zero.xyz/host/agentshelf.syntexa.ch/llms.txt)