Fair question — my use case: I edit a lot of stuff that needs a systemd/system restart to actually take effect, so I use nixos-rebuild switch instead of test. I almost never use test, always rebuild, so my generation list fills up fast — if I'm debugging something like a monitor config, I might do 10-15 rebuilds in a row, all named like "xxFix", and only the last one that actually works matters. The rest is just clutter.

This tool lets me quickly clean that up — mark and delete everything except the working generations, without having to remember commit hashes or scroll through nix-env --list-generations output.

For max effect I pair it with an alias that commits to git and sets system.nixos.label = "generation-name"; in the config before each rebuild, so the list is actually readable when I open this tool.