ISBN check
Validate an ISBN-10 (mod-11, trailing X allowed) or ISBN-13 (GTIN mod-10) book number. Length after removing spaces/hyphens selects the scheme.
Go to this service →Our latest check (2026-10-11)
- Answering
- Yes — valid x402 payment terms
- Time to answer
- 429 ms
- Price
- $0.002 per call
- Paying buyers, last 30 days
- 2 (directory's own records)
- Paid calls, last 30 days
- 2
- Category
- Developer tools and utilities
- Address
- https://checkdigit.openverbs.com/v1/isbn
Accuracy
Accuracy scores are published once a seller has enough paid checks against an independent record (at least 7 scored answers over at least 7 days). Until then no score is shown, and a missing score is never a pass.
For agents
This page as JSON: /sellers/56e8dbf805fb.json. Paid lookup by address: GET /api/seller?resource=… ($0.001, x402).