RambackDownloadFree up RAM on a Mac used for development
On a Mac used for development, most of the memory goes to tools that keep running after you stop using them: simulators, emulators, the Docker VM, Gradle daemons and dev servers. Stopping them is what frees RAM. Memory cleaners and sudo purge don't, because the memory belongs to processes that are still running.
Check whether you're actually short
Look at memory pressure and swap, not Memory Used. macOS fills spare RAM with cached files on purpose and drops them the moment an app needs room, so a Mac showing 15 of 16 GB used can be perfectly fine. You're short when the Memory Pressure graph in Activity Monitor turns yellow or red, or when swap keeps growing past a few gigabytes. From Terminal:
# how much memory macOS counts as free memory_pressure | tail -1 # how much has gone to swap sysctl vm.swapusage
System-wide memory free percentage: 23% vm.swapusage: total = 6144.00M used = 4505.75M free = 1638.25M (encrypted)
A free percentage that stays in the teens or lower while swap grows means macOS is writing memory to disk to make room, and everything gets slower.
What holds the memory on a dev Mac
These are the usual suspects. Each one is cheap to start again, which is why it's easy to leave five of them running.
| What | Typical size | Stop it with |
|---|---|---|
| iOS simulator | About 1.5 GB each, idle | xcrun simctl shutdown all |
| Android emulator | 2–4 GB each | adb emu kill |
| Docker VM | Up to its memory limit, even with no containers | Quit Docker Desktop, orb stop, colima stop |
| Gradle and Kotlin daemons | 1–2 GB each, for 3 idle hours | pkill -f GradleDaemon |
| Dev servers | A few hundred MB to over 1 GB each | kill the PID on the port |
| AI agent sessions | About 0.4–0.5 GB each, plus the servers they start | End sessions you've finished with |
| Xcode's build service | Often over 1 GB after a build | Quit Xcode |
Each name links to a guide with the full commands and the settings that make it smaller.
Why memory cleaners and purge don't help
sudo purge empties the file cache, which is memory macOS would have handed to the next app that asked anyway. Memory Used drops for a moment, then fills up again. The memory in the table above belongs to running processes, and nothing gets it back without stopping them. A cleaner that doesn't know what a simulator or a Gradle daemon is can't stop them safely.
Finding them in Activity Monitor
Activity Monitor lists all of these, under names that don't say what they are. An Android emulator is qemu-system-aarch64. The Docker VM is com.apple.Virtualization.VirtualMachine. A Gradle daemon is java. A simulator is dozens of small processes rather than one big one, so it never tops the list. Sort the Memory tab by Memory, and use the commands in the table instead of Quit, so each tool shuts down cleanly. What the dev processes in Activity Monitor are covers the rest of the names.
What to stop first
- Simulators and emulators you aren't using. They're the biggest, and they boot again in seconds.
- Idle Gradle daemons. The next build starts a fresh one.
- Dev servers from work you've finished, especially the ones an agent started and never stopped.
- The Docker VM, if nothing you're doing needs a container.
Leave databases and anything in the middle of a build alone. Stopping a database can lose data that wasn't written yet, and a stopped build just runs again from the start.