Your library should just take a *slog.Logger, and using *slog.Logger is an orthogonal choice to zap/zerolog/whatever. Those compete with slog.TextHandler or slog.JSONHandler, and sure, if you’re performance sensitive don’t pick them. In my newer projects I use zap under the hood with an application-facing *slog.Logger through go.uber.org/zap/exp/zapslog just fine (actually further locked down with my own interface so that coworkers can’t go crazy, but that’s beside the point). Your bespoke interface, or that standard interface you want isn’t going to be any more performant than going through slog.Handler interface anyway.