Macs slow down. It happens gradually — a sluggish app launch here, a spinning beach ball there — until one day you realize things are noticeably worse than they used to be. Sometimes it’s a process gone rogue. Sometimes it’s years of cached files and startup junk nobody bothered to clean up. And sometimes the hardware itself is running hotter than it should, throttling performance to stay safe.
Figuring out which one of those is actually your problem takes the right tools. Some are built into macOS and free; others are third-party apps worth paying for. Below are the ones that actually do what they claim.
⚡ Quick Answer
Start with Activity Monitor — it’s already on your Mac and will show you immediately if a process is hogging CPU or RAM. If you need to go deeper, dedicated Mac maintenance apps can handle cleanup, thermal monitoring, and catching things Activity Monitor won’t tell you about. In most cases, you don’t need more than two or three tools total.
Table of Contents
- Activity Monitor
- CleanMyMac
- iStat Menus
- OnyX
- DiskDiag
- Malwarebytes for Mac
- TG Pro
- Frequently Asked Questions
1. Activity Monitor
Cost: Free (built into macOS)
Before downloading anything, open Activity Monitor. It’s in Applications → Utilities, or just hit Cmd + Space and type it. This should always be the first stop.
The CPU tab shows every process running on your Mac and how much processing power each one uses. If something’s sitting at 80–100% and you have no idea why, that’s your problem right there. The Memory tab shows whether your Mac is actually running out of RAM—watch the “Memory Pressure” graph at the bottom. Green means you’re fine. Red means the system is compressing and swapping memory, which tanks performance.
Activity Monitor won’t fix anything on its own, but it tells you exactly where to focus. You can also force-quit a stuck or runaway process directly from here, which sometimes resolves the issue without any further digging.
2. CleanMyMac
Cost: Subscription-based (free trial available)
CleanMyMac is the most feature-rich option if you want one app to handle most common maintenance tasks—junk file cleanup, startup item management, malware scanning, and a general system health check.
The System Junk scanner is where most people see the biggest difference. Over time, macOS accumulates caches, leftover app data, and unused language files that never get cleared automatically. It adds up faster than you’d expect. The Login Items section is also worth spending a few minutes in — apps have a habit of quietly adding themselves to your startup list, which slows boot times and wastes RAM on processes you don’t need running.
It’s not cheap on an ongoing basis, but it’s genuinely useful if you’d rather not manage these things manually.
3. iStat Menus
Cost: $11.99 one-time (free trial available)
iStat Menus puts a live readout of your Mac’s CPU, RAM, GPU temperature, fan speed, and network usage in the menu bar where you can always see it. Once you’ve used it for a while, it’s hard to go back — knowing whether your Mac is actually working hard or just feeling slow is useful information.
The alerting feature is underrated. You can set it to notify you when a specific threshold is crossed: CPU temp too high, memory dropping below a certain level, a single process spiking. That’s how you catch problems before they become consistent slowdowns, not after.
4. OnyX
Cost: Free
OnyX has been around for a long time, and it does something specific: it lets you run system maintenance tasks that macOS is supposed to handle automatically but sometimes skips — particularly on machines that are frequently put to sleep rather than restarted. Clearing system and user caches, running UNIX maintenance scripts, rebuilding Spotlight’s index — all accessible from one place.
It’s a bit more technical than CleanMyMac, but not to the point where you’d need to know what you’re doing at a command-line level. Just make sure you download the version that matches your macOS release. OnyX is version-specific, and the developer keeps separate downloads for each release.
5. DiskDiag
Cost: Free (Pro version available)
Most people don’t think about their drive’s health until it starts failing, which is usually too late. DiskDiag reads the S.M.A.R.T. data your SSD or HDD reports internally — things like reallocated sectors, power-on hours, and temperature — and gives you a plain pass/fail health status.
It also breaks down storage usage by file type, which is useful if your disk is nearly full and you’re trying to figure out what’s taking up space without manually browsing through Finder. Not an exciting app, but a useful one to run every few months.
6. Malwarebytes for Mac
Cost: Free (real-time protection requires a subscription)
Adware and browser hijackers are more common on macOS than most people expect, and they often cause slowdowns that look like system issues but aren’t. Unexpected CPU usage, slow browser performance, redirects — these are classic symptoms.
Malwarebytes catches things Apple’s built-in security misses, particularly adware bundled with legitimate-looking apps. The free version lets you run manual scans; the paid tier adds background protection. If your Mac slowed down around the same time you installed something new, run this before you start digging into system settings.
7. TG Pro
Cost: $10 one-time
Thermal throttling is easy to miss because it doesn’t announce itself — your Mac just gets slower. When temperatures inside the machine climb too high, macOS automatically pulls back CPU performance to protect the hardware. On older MacBooks or M-series machines pushed hard for long sessions, this happens more than you’d think.
TG Pro shows you the temperature readings from every sensor on your Mac and lets you set custom fan speeds to get ahead of the problem before throttling kicks in. At $10, it’s a straightforward purchase if you do anything CPU-intensive for extended stretches — video editing, compiling, running local models, that sort of thing.
Which Tool Should You Start With?
Activity Monitor first, always. If that points you toward a specific issue — high CPU, low memory, disk problems — go from there. OnyX or CleanMyMac for accumulated system junk, TG Pro if things slow down under load, Malwarebytes if the timing lines up with a software install, DiskDiag if you haven’t checked your drive health recently.
You don’t need all of these. Most people are well covered with Activity Monitor, one cleanup tool, and iStat Menus running in the background.
Frequently Asked Questions
Does macOS really need third-party tools?
For basic maintenance, not really — macOS handles quite a bit on its own. But it won’t catch adware, won’t give you thermal visibility, and won’t clear everything that accumulates over years of normal use. Third-party tools fill the gaps, not replace what’s already there.
Will running these tools slow things down?
Menu bar apps like iStat Menus use very little background resources. CleanMyMac and Malwarebytes only run when you tell them to. Nothing on this list is the kind of software that sits there consuming resources constantly.
How often should I actually run maintenance?
Once a month is plenty for most people — a quick scan with your cleanup tool of choice and a look at your startup items. If you’re doing heavy work daily, keeping iStat Menus or TG Pro visible is a good habit.
Are any of these risky to run?
The tools listed here are all well-established and widely used. Be skeptical of generic “Mac cleaner” apps with aggressive advertising and vague feature descriptions— they can occasionally cause more problems than they solve.
