Ask HN: what features do you want in a geocoder? 12 years ago
One thing that I make use of but don't see too many services providing is some kind of 'match level' - where the geocoder returns a code indicating how confident it is about the quality of it's result. A result of 1 might mean a building level match, while 100 might be street level etc.
IIRC Google's geocoder does something like this, but it's pretty inaccurate, overstating it's match level consistently.
As others have said, geocoding is very hard to do well, but I commend the efforts being made with Nominatim and komoot/photon.