ISBN-13 check digit validator
Weight each digit 1 or 3 alternately from the left, sum, and require a multiple of 10.
9780306406157 is a valid ISBN-13: the check digit match.
A passing checksum only proves the number is arithmetically self-consistent. It does not prove an IBAN names an open account, an ISBN is assigned to a real book, or a card is active, unstolen, or has funds. Those require asking the bank, the ISBN registry, or the card network.
Try it: a valid example · a broken example
curl 'https://check-digit.gumballtools.com/api/v1/run?input=978-0-306-40615-7&format=isbn13'