Works pretty well from basic testing. I'm curious what this brings to the table over Soulver 3's existing QuickSoulver popup aside from capturing the selected text automatically. It feels like a quick Cmd+C then Cmd+V into QuickSoulver is not much more effort for the amount of times I could see myself needing access to a feature like this while in the context of Safari. Maybe it's another entrypoint for new potential Soulver customers if they find the extension on the App Store. (That said, I would love to see QuickSoulver get a feature to run as a system service on login so it's always available even when Soulver is not running.)

Would anyone be up for beta testing? https://share.getcloudapp.com/o0ugP05m

Would something like this be helpful? You could select some text before clicking the toolbar button, and have the expression field pre-populated with the text.