You don’t need to use link shorteners on Mastodon!
All links on Mastodon count as 23 characters towards your post limit, no matter how long the links actually are.
Link shortener services like bit.ly, t.co etc track users who click on their links. This is really bad for privacy. If you use link shorteners on Mastodon, people may assume you are just doing it for tracking purposes.
More info at https://fedi.tips/you-dont-need-link-shorteners-on-mastodon