Your project build folders are the biggest thing on your Mac

15 September 2026

Every framework writes its compiled output next to your source. Flutter puts it in build/ and .dart_tool/, Node in node_modules/, Gradle in build/, Rust in target/, Xcode in DerivedData. None of them ever delete it. A project you last opened in March still has its build folder from March. On one Mac that added up to 54 GB, with a single Flutter app's build/ at 20 GB.

Why it gets so big

• Flutter builds per platform and per mode: iOS, Android, macOS, debug, profile, release. Each keeps its own tree.
• node_modules is hundreds of megabytes per project, times every project you ever cloned.
• Rust keeps debug and release output plus incremental caches for every crate version you've compiled.
• Android adds NDKs: every version you ever installed stays under ~/Library/Android/sdk/ndk. Four of them is 11 GB.

Find it by hand

find ~/Development -type d \( -name build -o -name node_modules -o -name target -o -name .dart_tool \) -prune -print0 \
  | xargs -0 du -sh 2>/dev/null | sort -h | tail -20

That prints the twenty biggest, largest last.

What deleting costs

A rebuild. rm -rf build and the next flutter run regenerates it. npm install re-downloads node_modules. cargo build recreates target/. Minutes, not data. Don't delete it for the project you're building this minute; do delete it for everything you haven't opened in weeks.

What not to touch

A folder called build that actually contains source. Some repos do this. The tell is a manifest beside the folder: a package.json, pubspec.yaml, Cargo.toml or build.gradle next to it means the folder is output. No manifest, look before you delete. Leave ~/.pub-cache, ~/.gradle/caches and ~/.npm alone unless space is critical; they are shared downloads, and everything re-downloads slower without them.

In ddeploy

Developer section → Project Build Folders. Every folder is listed with its framework, git branch (and worktree) and when it was last built, so you can tick the one from March and leave today's. Old NDKs show up under Gradle. Deleted folders go to the Trash.

More on Mac storage: Old iOS simulator runtimes · Docker Desktop disk space · Time Machine local snapshots · WhatsApp media on a Mac