I love that it’s a command line tool — I’ll try it soon.
I use OpenIn for this [1] (it’s paid, but a one-time purchase at a very reasonable price). It works with URLs too, supports “browser profiles”, and lets you create logic using JavaScript (e.g., do X if the filename contains Y, or do Z if a modifier key is pressed).
It works really well and even has the ability to “fix” what external apps have changed. I plan to use this on new Macs to reconstruct my app associations and rules.
I do wish the rules were defined in plain text files — sometimes it’s hard to follow the logic through the UI and the way it handles things.
Another comment mentions Hammerspoon (which I used in the past — it was very nice). Maybe I can rebuild part of my current setup with it.