Homebrew still lists apps you deleted: why, and how to clear the records

Why does Homebrew list an app I deleted?

Every cask Homebrew installs gets a folder in /opt/homebrew/Caskroom named after it, with a subfolder per version. Dragging the app to the Trash does not touch that folder, so the record stays. Apps that update themselves make it worse: the record stays at the version Homebrew installed.

That was our Mac: four of nine casks were records of apps that were gone.

How do I find stale casks?

for c in $(brew list --cask); do
  printf '%s: ' "$c"; du -sh /opt/homebrew/Caskroom/$c | cut -f1
done

A record of an app you deleted is a few kilobytes, because the app it describes is gone. Real apps that Homebrew moved to Applications are small here too, so confirm in Applications before you act.

How do I clear them?

brew uninstall --cask --force alfred ghostty visual-studio-code

--force tells Homebrew to clear the record even though the app is missing. Add --zap to also remove the app's Library folders, which has its own catch.

Find what is left in one look

Free Mac's Apps tab lists what is really in Applications, with each app's leftovers, and its Storage map shows Homebrew's folders. What you pick goes to the Trash. Removing Homebrew altogether is in uninstalling Homebrew.

Related: the Chrome Apps folder and uninstall Rust.