Standard Problems
What some might call “classical go problems” we call “standard” on this site. These problems are local, tactical, require no special instruction, and have a clear outcome.
Other Problems
Many users on goproblems love contributing weird problems – for example requiring following special rules, or the formulation is very not realistic (ie, wouldn’t happen in a real game). Even normal problems can have extra instructions which make them challenging, like an option to tenuki. These problems are interesting in their own way, and can be useful for studying, but we don’t consider them part of the standard problem set.
Lifecycle of a problem
The problems here are all community contributed. That means anyone can add a problem, and over the years, thousands of unique people have done so!
When a problem is first added, it doesn’t have a rating set. People will try it and the rating will adjust. Also, new problems often have small mistakes that get corrected by the author over time.
When a problem has been tried enough times to have a stable rating, plus the quality has been marked as good by users trying it, plus there aren’t flagged issues, and it is a “standard” problem, then it gets marked as “canonical” and will be added to the set of problems considered reliable and good candidates for showing to users in a normal user flow.