To be fair it's going to be nontrivial to implement all the codes everywhere. In some cases it's going to be impossible for an app like this to judge - In the UK, for example, there are "permitted development" rights which allow certain things (like a garden office or other outbuilding) without going through a bureaucratic process. But while some of the rules are easy to automate (eg, must be less than 2.5m high) some are not. For example, the UK allows building over 50% of the garden[1]. But if it was just measurement based, you'd be able to build over 50%, then 50% of the remaining 50%, etc etc. So the rule is "50% of the original garden". That's going to be difficult for an app like this to find out.

[1] it's slightly more complicated than this