Canadian · Validation
ISMN check digit validator.
Verify a 13-digit ISMN (International Standard Music Number, the ISBN-like identifier for printed music, always starting 979-0), or enter just the first 12 digits to have the check digit computed for you. Everything runs in your browser: nothing you type is transmitted anywhere.
Inputs
Result
Enter an ISMN and press Validate.
How the ISMN check digit works
A 13-digit ISMN is the prefix 979-0, eight digits of registrant and item numbers, and one check digit. Per the ISMN Users’ Manual, each of the first twelve digits is multiplied by an alternating weight of 1 and 3 from the left (starting with the first “9”), and the products are summed. That sum plus the check digit must divide evenly by 10, so the check digit is (10 − sum mod 10) mod 10.
The manual’s own worked example, 979-0-3452-4680-5, gives a weighted sum of 95 for the first twelve digits; 95 + 5 = 100, which is divisible by 10, so it is valid.
This tool checks the current 13-digit form only. The retired 10-digit form beginning with “M” is not handled.
What a passing checksum does and doesn’t tell you
A valid check digit only proves the digits are internally consistent — it does not confirm the number was ever assigned to a real publication by an ISMN agency. This tool runs entirely in your browser: nothing you type is transmitted, stored, or logged.