Note: 33

TIL that the Mastodon Statuses API (the one you call to make new posts) counts the length of the spoiler_text towards your 500 character limit.

I wish the error message (“Text character limit of 500 exceeded”) was more explicit. It took me ages to figure out why my 470 character post was causing this.

This behavior is clearer in the Mastodon UI itself, where the character number ticks down as you type in the Content Warning textbox.