This would be a web app (either entirely client-side or with some light client-server interaction) that could load GeoJSON and TopoJSON files, draw the features (and list their properties), then allow you to perform TopoJSON conversion and other operations (simplification, merging, joining data, etc.) and see the results on top of the original. This would take some of the guesswork out of simplification and quantization parameters, and could even allow you to save out your operations as a script for use elsewhere.
This would be a web app (either entirely client-side or with some light client-server interaction) that could load GeoJSON and TopoJSON files, draw the features (and list their properties), then allow you to perform TopoJSON conversion and other operations (simplification, merging, joining data, etc.) and see the results on top of the original. This would take some of the guesswork out of simplification and quantization parameters, and could even allow you to save out your operations as a script for use elsewhere.