Luhn Checksum

The mod-10 check behind card numbers and IMEIs, demoing the p/moul/x/daily/luhn library.

Append a number to the path to check it — spaces and hyphens are ignored.

Samples

number	valid?	note
79927398713	✅ valid	the textbook example
79927398710	❌ invalid	same number, wrong check digit
4539148803436467	✅ valid	a test card number
4539148803436647	❌ invalid	same card, two digits swapped

Luhn is a typo check, not a security check: it catches every single-digit error and nearly every swap of adjacent digits, but anyone can compute a valid number. Never authorize anything with it.