I'll see if I can roll this into a future update for !instance_assistant@lemmy.ca . I wanted to try and get a "post to Lemmy" button working, and this is a part of that. Looks like the reddit one was done using a Reddit API, and while the Lemmy ones are different it shouldn't be too bad.
UPDATE: I'm able to search for links within the body of posts, but haven't figured out why it doesn't search the links yet. I'll look into it later
The only limitation might be that the search is limited to a particular instance. Since there is an unlimited number of instances, I don't think there's an easy way to search them all without some external service doing some caching of some kind. We could have it search a bunch of different instances, but I want to minimize unnecessary / spammy requests.
@Bucky@816am.ddns.net, is it important for the extension icon to display the number, or did you usually run a manual search?****