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 suspend 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

Tips on using the FediBlock hashtag

Writing posts about FediBlock

The Hashtag FediBlock is watched by a lot of admins (and mods) regularly so they know which instances to block. It can be very useful, but sometimes it's a real mess going through the FediBlock timeline, because of all the posts that shouldn't be there. Here are some tips.

When to use the hashtag

Use #FediBlock to post about:

an offensive instance, even if it has been posted about (a lot) before (just maybe check if the last 5 posts under the hashtag are not already about that instance)
an instance (currently) spamming (maybe indicate, that a limit is better, than a suspend in this case)
a general useful tip about fighting spam or trolls or whatever (think about whether it doesn't fit better under #FediBlockMeta)
recommendations to unblock an instance that is e.g. no longer spamming

When not to use the hashtag

don't use it for this	instead do this
General discussions about FediBlock	use #FediBlockMeta
replies to posts telling OP to use the hashtag if they forgot	either write e.g. # FediBlock or do use the hashtag, but make your post unlisted, so it won't appear in the TL
telling someone to check out FediBlock	post a link or do use the hashtag, but unlisted
Thanking people who are active on FediBlock	use #FediBlockMeta
personal grudges (this is a hard one, because in your eyes, there might be a legit reason to block)	try to keep it to yourself
long threads about one instance	give the first post the hashtag and indicate, that it's a thread. Exception: replying to your own post after a (long) time with additional info
ranting about FediBlock, shitposting or trolling under the hashtag	if you have to do this, do it in a way that makes absulutely sure everyone understands, that you and/or your instance should be blocked
don't excessively use the hashtag for block recommendations for single users on otherwise good instances	it would be good to have another hashtag for that

General tips on using the hashtag

use CWs e.g. with the name of the instance (so admins who already block that instance can move on quickly) + the offense (people who don't follow the hashtag will still see the post but shouldn't be confronted with despicable things if they don't choose to see them)
if your post is about multiple instances use paragraphs, bullet points and lists in a way that the instances are quickly visible and not hidden somewhere in the running text (again for admins already blocking those instances)
recommend blocking the main domain, if the instance is on a sub-domain unless the main domain is that of a big instance hosting company that might get rid of the offending instance soon anyway. Do indicate however, what the sub domain is, so admins can check it out themselves
you don't have to give receipts, but a block recommendation without a receipt and without a block reason is mostly useless
think about censoring your receipts, especially screenshots. You don't want to e.g. spread loli porn.

Following the FediBlock hashtag

Filter posts you already processed.
On Mastodon you can go to Settings > Filters > Add new filter. Give the filter a name (e.g. just use the ☑️ emoji), select expire:never, tick "public timelines" and optionally "home and lists" and "profiles", choose "hide with a warning", don't add a keyword, instead click the little x to remove the field to add a keyword and then hit save.
Now you can go through the hashtag's timeline and once you read a post and blocked the instance, or decided not to, or whatever, click on the three-dots-menu below the post, select "filter this post" (it's one of the options written in red) and select the filter you defined before.

If you're on a small instance, think about getting an account on a larger instance just to follow the hashtag. You'll discover a lot more #FediBlock posts on an instance that federates with lots of instances already. If you do that however, block the instances that you block on your own instance on that account too, so you don't see posts by trolls on those instances abusing the FediBlock hashtags.

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