Base36
Digits and letters, the URL-friendly base.
Where it came from
Base36 uses the ten digits and twenty-six letters — exactly the characters in the English alphanumeric set. Because it is case-insensitive, it is safe in places that mangle case: URLs, file names, and human-shared IDs.
You have seen it in YouTube video IDs and URL shorteners, where a number like 12345678 becomes the shorter, friendlier "7CLZI".
How it works
It is positional like any base: each digit carries 36^n. Converting a byte string to Base36 is straightforward grouping of bits into 5.17-bit chunks — implementations just map values 0–35 to 0-9 then A-Z.
UWC turns raw bytes into Base36 and back entirely client-side. For case-sensitive, higher-density IDs, Base62 (adds lowercase) is the sibling.