Yo admins! In preparation for a better joinmastodon.org sign-up wizard, https://instances.social directory now lets you set a category for your instance, in the admin area.
The categories are: art, music, books, activism, sports, games, tech, academia. It's ok to not have a category, too, like for example octodon.social is just a general purpose instance. But if yours is themed, you better categorize it.
If you think a crucial category is missing, tag @TheKinrar