ISBN Check — pay-per-call API

Name: code402 — ISBN Check
Price: 0.000999 USD
Author: code402

$0.000999 per call · 20 free calls/day · no signup · pay with card credits or a signed USDC voucher (x402)

Validate an ISBN-10 (mod-11) or ISBN-13 (1,3-weight mod-10) checksum.

Honest scope: Checksum-verifiable: a real check-digit algorithm runs offline, so a malformed or transposed identifier is rejected deterministically. It does NOT prove the account/record exists or that its holder is honest — pair with your existing fraud process.

Try it (first 20 calls/day free)

curl -X POST https://code402.dev/v1/tools/isbn-check/call \
  -H "content-type: application/json" \
  -d '{"isbn":"978-0-306-40615-7"}'

No key needed for the free tier. When the free quota is used up, the API replies HTTP 402 with the exact price — agents sign the x402 voucher and retry; humans buy card credits. Every paid response carries a signed receipt you can verify offline.

Run it in the playground (free)Pay by card — credits, no crypto

Input parameters

Field	Type	Meaning
`isbn` (required)	string	ISBN-10 or ISBN-13; dashes/spaces allowed.

Response

Top-level fields: tool, valid, normalized, country, reason, scope. Paid responses also carry a signed XDR-1 receipt.

All code402 tools

Machine-readable catalog: llms-full.txt · MCP manifest · OpenAPI. Operated by JUANA LIMITED (UK Co. No. 14043409). Non-custodial: USDC settles payer→seller directly on Base.