No, also works on new projects. We do recommend you set up "standards" first though, a documentation of how you want things to be done, for example how you do auth, how you handle multi-tenancy, how migrations work, whatever applies to your new project. The whole point of spec-driven is not not let AI wing it, but be very prescriptive.

We include a couple of templates to make that easier - NextJs + Convex + ShadCn/ui, NextJs + Supabase + ShadCn/ui, etc.