I have two questions mainly:

1. Is there an existing tool like this? Or maybe even a built-in way to check on a per instance basis if it’s currently federated with another instance or not?

2. What’s the default state of an instance once it starts up? I’m guessing open to all, and defederation has to be an intentional choice?

Overall I’m just curious. I don’t have the capability to code something like this myself, but I’d be pretty interested to check on the links between instances as the Fediverse grows.