ISBN Validator (ISBN-10 and ISBN-13)

Choose this endpoint when you need to validate the check digit of a specific ISBN-10 or ISBN-13 book identifier. It automatically selects the correct algorithm (mod-11 for ISBN-10, GTIN mod-10 for ISBN-13) based on length, and handles hyphens and spaces natively. Prefer this over a generic Luhn or GTIN validator when you know the identifier is specifically a book ISBN and want ISBN-aware validation including the trailing 'X' allowed for ISBN-10.

• ISBN string is empty or missing — returns validation error
• Length after stripping hyphens/spaces is not 10 or 13 — scheme cannot be determined, returns error
• Check digit does not match computed checksum — returns invalid result
• ISBN-10 check digit is not a digit or 'X' — returns invalid
• Non-numeric characters other than hyphens, spaces, or trailing X present — returns error
• Network or payment failure may prevent the call from completing