Hi, I am not sure if there is a way already to do it, but it would be helpful to have FilletCurve work with a interactive radius preview. Currently we have to know the radius to fillet and while tracing maps or shapes quite often the radius is just a visual thing, the numbers don’t matter. The closest tool to be used is Arc - Tangent to Curves with nice interactive preview, but it still requires several extra clicks to re-trim them to the radius. Maybe Fillet command option “Interactive=Yes/No”? if yes, after picking both curves to fillet we could mouse-move to adjust the fillet radius and on confirm click Rhino would add fillet/trim the curves?