I used to use Zod until I realised it’s rather big (for many projects this isn’t an issue at all, but for some it is). Now I use Valibot which is basically the same thing but nice and small. I do slightly prefer Zod’s API and documentation, though.

Edit to add: aha, now I read further in the announcement, looks like @zod/mini may catch up with valibot -- it uses the same function-based design at least, so unused code can be stripped out.