> Trying to jam in the extra characters for "efficiency" also doesn't really do much. Base84 is 6.4 bits per character, base64 is a flat 6 bits per character, base58 is 5.86 bits per character.

Also on efficiency, you are trading off code complexity for a little extra storage: base64 is a nice round 6 bits per character meaning every three bytes encoded is four output. Neither base84 nor base58 align on convenient bit boundaries like that so choosing the output character is more faf. Padding could be more complicated too.

Now if you are looking at a per-character limit where the characters are multi-byte (say SSMS shortcuts which are limited to 32767 UCS2 characters) then some form of base4096 (12 bits per character so three 8-bit bytes to two output characters) might be useful. Yes, I have done this: putting a long analysis proc (a replacement for sp_help & friends) into a “shortcut” I was getting close to the 32K-char limit so compressed and base64ed the code and included an unpacker. This was more than enough to deal with the problem (TBH, just stripping comments would have done!) and simplified things in some ways as I no longer needed to escape quotes and such, but I went one step further played with writing a B4096 encoder because I like playing with that sort of silliness. I went with 4096 due to aligning nicely with 4-bit boundaries, and finding 4096 useable characters (avoiding control characters, undefined codes, and other unprintables) is easy. If the limit is actually 32767 or any Unicode characters (including those not in the UCS2 or UTF16 base plane set) then you could perhaps get even more daft though I'm pretty sure it is just 16-bit characters and not full Unicode.