1. Open Terminal.
2. Before making changes, check whether a specific folder is already excluded: tmutil isexcluded /path/to/folder — this returns a simple yes/no style answer.
3. To exclude a single folder from all future Time Machine backups: sudo tmutil addexclusion /path/to/folder (you’ll need to enter your admin password since this requires elevated privileges).
4. For excluding an entire directory tree recursively — useful for something like a Docker data folder — add the -pflag: sudo tmutil addexclusion -p ~/Library/Containers/com.docker.docker/Data/vms
5. To see a full list of everything currently excluded, including exclusions set through the GUI: tmutil listexcludedfiles
6. If you change your mind and want a folder backed up again: sudo tmutil removeexclusion /path/to/folder
7. For power users, you can batch-exclude several developer-related folders at once by writing a small shell script that loops through common offenders, like node_modules, .cache, DerivedData, and any local VM disk images, then run it once after setting up a new Mac.

One thing worth noting: exclusions set via tmutil persist across Time Machine’s exclusion list and will show up (though sometimes greyed out) in System Settings → General → Time Machine → Options, confirming the change took effect. This approach is particularly valuable for anyone doing local development work, since build artifacts and dependency folders can easily add tens of gigabytes to a backup that offers zero real recovery value if lost.