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ISIN validator

Check whether an ISIN’s country prefix and check digit are valid.

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ISIN validator
Paste one or more ISINs (International Securities Identification Numbers) and this tool checks whether each one is structurally valid: a two-letter country prefix, nine alphanumeric characters for the national security number (NSIN), and a check digit computed with the modulus 10 double-add-double rule. It is built for developers, back-office and compliance staff who need to sanity-check a batch of identifiers before importing them into a system, without uploading anything.
Batch mode treats every line as its own code, so you can paste a whole column pulled from a spreadsheet; turn it off to check only the first code you enter. "Tolerate spaces and lower case" strips whitespace and normalizes case before checking, matching how ISINs are often copied from PDFs or emails. "Show country by full name" adds the resolved country next to each result, and "recognize special XS/EU prefixes" accepts the two non-country codes ISIN also issues — XS for internationally cleared securities and EU for pan-European instruments — alongside the standard ISO 3166-1 list.
If you have an 11-character code with the check digit missing, turn on "compute missing check digit" and the tool derives it and shows the completed ISIN. Choose whether the output lists every row with a reason, or only the rows that fail — handy for cleaning a large list down to the codes that need attention. The tally below the output always reports how many codes were checked and how many passed.
Everything runs locally in your browser using plain JavaScript: no code is ever sent anywhere, which matters for identifiers tied to holdings or transactions. When you are done, copy the result, download it as a .txt file, or send it to another tool's input to keep working.
FAQ
What exactly does this tool check?
It verifies the structure of an ISIN: a recognized two-letter country (or XS/EU) prefix, nine alphanumeric NSIN characters, and a check digit that matches the ISO 6166 modulus 10 double-add-double calculation. It cannot confirm the security actually exists or is currently traded.
How is the check digit calculated?
Letters are expanded to two digits each (A=10 up to Z=35), the resulting digit string is processed from the right, and every second digit is doubled (with its own digits re-summed if the double exceeds 9). The check digit is whatever brings the total to a multiple of 10.
Can it complete an ISIN that is missing its check digit?
Yes. Turn on "compute missing check digit" and paste the 11-character country-plus-NSIN part; the tool derives and appends the correct check digit.
Why would XS or EU appear as a country prefix?
XS is used for securities cleared through Euroclear or Clearstream rather than issued from a single country, and EU is used for some pan-European instruments. Both are recognized when "recognize special XS/EU prefixes" is on.
Is my list of ISINs uploaded anywhere?
No. Validation runs entirely in your browser — the codes you paste never leave your device.