App Tamer Lets You Manage CPU Utilization on a Per App Basis

Don't Let Background Apps Rob Your Mac of Its Performance

App Tamer window

Coyote Moon, Inc.

App Tamer from St. Clair Software can take control of a wayward app that's hogging CPU utilization and stop it in its tracks. Unlike Apple's App Nap, which puts an app to sleep when its active window becomes covered by one or more windows, App Tamer can work to control both active foreground apps and apps that work in the background, such as Spotlight or Time Machine.


  • New user interface that provides quick access to unruly apps.
  • Auto Limit is able to allocate a percentage of CPU to an app.
  • New App Tamer engine is streamlined to reduce its own CPU footprint.


App Tamer is an easy-to-use utility to help you control how your Mac utilizes its CPU resources and assigns them to the various running apps and services. Although App Tamer is a very easy app to use, it is by its nature an app for advanced Mac users, who have a good understanding of how apps interact to use processing resources, and how that affects other variables, such as battery runtime.

Installing App Tamer

Installation is straightforward, with just one little detail you need to be aware of. Installing App Tamer involves dragging it to your /Applications folder and then simply launching the app. The first time you use App Tamer, it will install a background helper app it uses to monitor processor usage. Aside from the helper installation, which only requires your administrator password, App Tamer installation is as easy as it gets.

Uninstalling App Tamer

Should you decide App Tamer is not for you, you can uninstall the app by simply quitting App Tamer, and then dragging the app to the trash. For a complete uninstall, you can also delete the helper tool located at: /Library/PrivilegedHelperTools/com.stclairsoft.AppTamerAgent.

Using App Tamer

App Tamer does most of its work in the background and only presents itself to the user as a menu bar item. Through the menu bar, App Tamer provides graphs showing overall CPU usage, CPU usage by app, and CPU usage saved by App Tamer. Just below the graph, the App Tamer window shows a list of all the apps and services currently running; an additional section shows the apps that App Tamer is actively managing.

Managing Apps

App Tamer's number one job is to manage how an app uses your Mac's CPU resources. One of the simplest uses of App Tamer is to intervene when an app is out of control and using excessive resources. This can usually be noticed as your Mac becomes sluggish when trying to work with other apps, or you hear your Mac's fans spin up as the internal temperature rises from excessive CPU usage.

When this happens, you can simply click on the App Tamer menu bar item and take a quick look at the Running Process list to see which item is hogging CPU usage. You can then either right-click the app name and select Force Quit from the popup menu, or for an approach that's a bit more subtle, you can assign the app to be managed by App Tamer.

Each app in the App Tamer window includes a small square next to its name. Clicking on the square allows you to set up how App Tamer will manage the app. You can choose to have App Tamer completely stop the app whenever it isn't the front most app, or you can slow down the app, restricting it to a percentage of available CPU time.

App Tamer comes preconfigured to manage a few popular apps, including Safari, Mail, Google Chrome, Firefox, Spotlight, Time Machine, Photoshop, iTunes, and Word.

For the most part, the preconfigured apps have their App Tamer management settings pretty well set up. For instance, Word is set to completely stop if the Word window isn't the front most window. This makes sense, as there's little reason to have Word grabbing resources when it doesn't have much to do.

Mail and Safari, on the other hand, are set to slow down when they're in the background. Not a bad idea, since it allows both apps to continue to work on downloading messages or updating a web page, but doesn’t allow some out-of-control ad in Safari to drain your Mac's battery.

Final Thoughts

App Tamer is easy to use and can be an effective tool for extending battery life or keeping your Mac running cool on hot summer days.

It has its quirks, some not of its own making. For instance, I mentioned the problem with beach balls. This can occur when a running app, such as your browser, is stopped or has limited CPU utilization. As you move your pointer around on your Mac, when you move across the browser window, the cursor will likely change to the spinning beach ball.

An annoyance at best, if you remember that you configured App Tamer to manage the app, but it can also be a moment of panic if you forget that you set App Tamer to disable a background window.

It's not App Tamer's fault; it's just a quirk in how the Mac works. Nevertheless, it can be a bit of a surprise.

App Tamer does exactly what the developer says it can do: manage a Mac's CPU utilization on a per app or service level, something you can’t do easily on your own. Its interface is well-designed and intuitive to use. I like the running graphs as well as the percentage of CPU utilization listed for each running process.

For the advanced Mac users who want to control their Mac's performance on a per-app basis, and who really like taking an active role in how their Mac works, App Tamer may be a good choice.

App Tamer is $14.95. A demo is available.