There are a few different character limits in Short.
Long URLs
We can shorten URLs up to 2,048 characters in length. This includes all punctuation marks.
This limit also applies to the links you use for QR Codes and buttons on Short Pages.
Short Links
The character limit for a custom back-half of a link is 255 characters. Refer to the “What characters are supported for custom link customization?” page to see which characters are allowed.
Custom Domains
The maximum length for a custom domain is 32 characters, including the dot.