# Delx ISBN Check

> Delx ISBN Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-11).

Validates ISBN-10 and ISBN-13 checksum correctness for a given ISBN string

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/isbn-check?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/delx-isbn-check-3ca6380e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_rclJQ1UMrfD3UsrSNRisn

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 delx-isbn-check-3ca6380e -d '<json body>'
```

Example prompt: Can you check whether 978-3-16-148410-0 is a valid ISBN-13 with a correct checksum?

## When to prefer this

Use this endpoint when you need a lightweight, programmatic checksum validation of an ISBN-10 or ISBN-13 identifier before storing, querying, or displaying it — especially in automated catalog pipelines, user-input sanitization flows, or data quality checks where calling a full book metadata API would be overkill.

## Known failure modes

- Invalid or missing ISBN input returns a validation error
- Non-numeric or malformed ISBN string (wrong length, unexpected characters) returns invalid result
- Network timeout or service unavailability
- Payment failure via x402 protocol preventing the call

## How this service works

ISBN-10/ISBN-13 checksum validation for $0.001 USDC. Call when you need this bounded result without an API key or subscription. Returns machine-readable JSON via x402 on Base or Solana. Limitation: results cover only the supplied input or one bounded public endpoint at request time; callers must verify before acting.

## Output

Returns whether the provided ISBN string passes checksum validation, along with the detected format (ISBN-10 or ISBN-13) and the validation outcome (valid/invalid).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input",
  "output"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "additionalProperties": true
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST",
      "PUT",
      "PATCH"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type",
    "example"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "json"
    },
    "example": {
     "type": "object",
     "additionalProperties": true
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {}
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/delx-isbn-check-3ca6380e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)