how can I check which instances my instance (lemmy.world) has defederated from? Is there also a way to check which instances have blocked lemmy.world?

https://federation-checker.vercel.app

Great thanks. This shows both who has blocked an instance and who that same instance is blocking.
I want to add that to see who is blocking lemmy.world do you need to type with lowercase. I didn't see the list of "blocked by" when I wrote lemmy with a capital l.
Very helpful, thanks. Now I'm curious as to why they are blocked?
- Now I'm curious as to why they are blocked?
  We can't confirm whether or not you're curious. Only you can decide that.
Thank you!
Would you know of something similar for kbin? This only tracks Lemmy instances.
- I don't, sorry. I only use Lemmy.

Search in page "blocked"

Perfect. Thanks.

I get the idea of federation etc now in terms of the fediverse but when something is defederated does that just mean it’s not integrating with all the others/the one I am currently on?

Like I am on Lemmy.world and for arguments sake I can view posts etc on Lemmy.bullshit cos it’s federated. Then Lemmy.bullshit ends up being full of nutballs and Lemmy.world admins cut ties with them so I can no longer see their stuff from my instance and is now ‘defederated’, is that right?

That's how I have experienced it.
Yes, we only see stuff from lemmy.bullshit to the point where lemmy.world were still in sync. So we can only see lemmy.world users interactions with post from lemmy.bullshit after the defederation. The same goes for them they can't see lemmy.world users interactions either. because what lemmy.world users are interacting with is a copy (of lemmy.bullshits original post) and isn't sending the updates back to lemmy.bullshit and the other way around, the original isn't updating the copy.
Yeah, my understanding is that defederation prevents any incoming communication, so you won't see any posts or comments that come from lemmy.bullshit, however users from lemmy.bullshit will still see all of your comments and posts from lemmy.world unless they choose to defederate you back.
- however users from lemmy.bullshit will still see all of your comments and posts from lemmy.world unless they choose to defederate you back
  see, but not interact with, is that right? Or can they still reply, but it'll only show up on their end (and for whoever they're still federated with)?