Luhn Algorithm Check
Checks card numbers, IMEIs, and other numbers with the Luhn algorithm, computes the check digit, and shows the calculation step by step.
Spaces, hyphens, and periods are allowed. The number is not sent anywhere.
Up to 100 numbers. Empty lines are skipped.
| № | Number | Check | Type and hint |
|---|
Step-by-step calculation
The Luhn algorithm catches typos: one wrong digit and almost any swap of two adjacent digits. The only swap it misses is 09 and 90. Bank card numbers and phone IMEI numbers are checked with it.
A passing check only means the number is written without a typo. Whether the card actually exists, the algorithm cannot tell: a number made of all zeros passes the check too.
Check digit and error search
Given a number without its last digit, the tool calculates the check digit. If a number fails the check, the tool shows the swaps of adjacent digits that make the number valid. Which exact digit is wrong, the algorithm cannot say: a single wrong digit can be corrected at any position in the number.
Rate this tool
Help us get better
Tell us what was missing.
Other tools
JSON Formatter
Format and repair JSON in the browser, flagging duplicate keys and long numbers
Regex Tester
Regex testing with a plain-language breakdown and hang protection
JWT Decoder
JWT parsing with fields explained and signature verification
CSV to JSON
A table to JSON with honest types and a reverse check
JSON to CSV
JSON to a table for Excel, with verification and formula protection
SQL Formatter
A readable query layout, verified against the source, with risky spots flagged
XML Formatter
Readable XML, errors explained with a hint, verified against the source
XML Validator
Markup, XSD schema, sitemap, YML and RSS rules, with the path to each error