FediBlock

This article was once a public blocklist of evil instances and is now instead just a general article about blocklists and the FediBlock hashtag.

Background

As a moderator or admin of any instance of the Fediverse you will sooner or later be confronted with people from other instances who harass, discriminate or troll your instance's users. And often lots of these users are on the same instance. If you want an unnecessary and hard challange during your moderation work, you'll suspand each user individually, after they did something wrong, but most moderation teams will decide to block at least some instances, that are just full of evil people and are encouraged by their instance's moderation team and rules to troll and harass the rest of the Fediverse.

Some admins will be more strict and block more instances, others less so. One reason why an admin might be strict is because they, or the community they watch over, are part of one or more marginalized groups.
Basically there is a spectrum ranging from instances that aim to be safe spaces for everybody and so called "free speech instances" (although they don't even understand what free speech is.
Fun fact: Whether an admin decides to be more strict or not or even whether they block your instance or not is only their own buisnes.

Origins

Since Mastodon and the rest of the Fediverse have no shared or federated moderation tools there has long been a need to share instance blocks or blocklists publicly.
That's why the hastag #FediBlock was invented and is still widely used in the Fediverse to share information about bad actors. The hashtag was started by long time Black fedizen Marcia X who has also been maintaining it by educating people about it/helping them with using it.

Unfortunately the hashtag has long also been a target of shitposts and open hostility against those using it.
Because of this and to keep a better overview of blockworthy domains fediblock.org was started, but later stopped again. The same happened with @fediblock@a.rathersafe.space later, and then again with the blocklist Fedizen:PaulaToThePeople maintained in this very article.
Now below are some current public blocklists

Public blocklists

• FediSeer by Rikudou
• Gardenfence by Brook
• Oliphant's blocklists by Oliphant
• Seirdy's blocklist by Rohan “Seirdy” Kumar
• The Bad Space by Ro (atm the list is at tweaking.thebad.space

Other links

• FediPact is kind of an opposite of a blocklist. It lists instances that are committed to blocking Threads (the Meta "Fediverse" platform)