All tools › Identifiers and check digits
Check digit calculator
Luhn, GTIN, ISBN, modulo eleven and the two ISO 7064 rules, with the working digit by digit.
It runs entirely in this browser tab: what you type is never uploaded, and the tool makes no network request while it works. Open your browser's network panel and try it — nothing leaves the page. There is no sign-up and no limit beyond what your own browser can hold.
Settings
- Algorithm
- Working it out is a guess: length is the only clue, and eight digits is a barcode and a Danish tax number alike. Choices: Work it out, Luhn, GTIN / EAN / UPC, ISBN-10, ISBN-13, Modulo 11, ISO 7064 mod 97-10, ISO 7064 mod 11-10.
- What to do
- Choices: Check the one that is there, Work out the missing one.
- Show the working
- Replaces the answer with how it was arrived at, step by step.
How to use it
- Paste your text into the box above, or open a file.
- Adjust the settings beside it until the result is what you wanted.
- Copy the result, or save it as a file. The result updates as you type.
Questions
- Is what I type uploaded anywhere?
- No. This page carries the whole tool as WebAssembly and runs it on your own device. Nothing you type is sent anywhere, and there is no network request to make while it works.
- How exact is the arithmetic?
- Exact, in decimal, for everything the tool was given: no value here is put through floating point on the way to the answer. Where there is a genuine ceiling — thirty-nine digits for the number-theory tools, a fixed number of places for a repeating fraction — the tool says the limit rather than quietly truncating.
- Can I get this result again later?
- The settings travel in the page's address, after the #, so a link reproduces them exactly — and the fragment of an address is never sent to a server. Your last settings are also remembered on this device, which is worth knowing before you paste a number you would not want left there.
- Is there a version that is not a web page?
- Yes. The same tools are built as a desktop application from the same code, with a save dialog instead of a download and no network code at all.
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