is it possible to get prefect to take in a boolean parameter? Or do all parameters need to be strings?

They just need to be JSONSerializable. Pretty sure it can be a boolean. You running into something?

haven't run into an error yet. but I've been trying to search documentation on boolean parameters and couldnt find anything. Ideally, the prefect UI would show a toggle switch and not a text box for this parameter to signify theres only 2 options

@Marvin open “Feature Request: Toggle switch for Boolean Parameters” in UI

Are you expecting a registered Flow Parameter’s type to be inferred and the display changed in the UI? So that is not possible. But if you select a Parameter in the UI, there is a Radio button that shows up

if I set a default value for a parameter, in the UI it will have selected a type. I'd like to specify in the code what type the parameter should be without having to specify a default value. Is that possible?

Not for current Prefect, but yes this is readily available in Prefect 2.0 (Orion) where type annotations of your tasks are used to coerce the inputs.