PC cleaning apps are digital snake oil. The web is full of ads for applications that want to “clean your PC” and “make it feel like new.” Don’t pull out your credit card — these apps are terrible and you don’t need them.

If you do want to “clean your PC,” you can do it for free. Windows includes built-in PC cleaning tools that can do almost all of what the average PC cleaning app will do for you.

Let’s Investigate a PC Cleaning App

So what do these apps do, anyway? To investigate, we ran MyCleanPC — don’t try this at home; we installed this bad software so you don’t have to. MyCleanPC is one of the most prominent PC cleaning apps — it even advertises itself with television commercials.

We’re already on thin ice here — Windows can remove junk files, clear Internet browsing traces, and defragment your hard drive without installing additional software.

MyCleanPC offers a “free diagnosis,” which is little more than an attempt to scare people into thinking their computers have thousands of “issues” that can be fixed for an easy $39.99 payment.

After running a scan, you’ll see an alarming count of the number of problems on your computer. It found 26267 issues on our computer. That’s an extremely alarming number — but what exactly is an issue?

Every browser cookie and history entry counts as a single issue. Every temporary file counts as a single issue, no matter how tiny it is. Invalid registry entries are considered issues, although they shouldn’t actually slow down your computer. Our registry can be compacted a bit, but this shouldn’t make a noticeable different in performance Every fragmented file counts as a single issue. MyCleanPC is measuring fragmentation based on the number of fragmented files, leading to a scary-looking 21. 33% data fragmentation statistic. For comparison, the Windows Disk Defragmenter tells us we have 2% fragmentation.

Now that they’ve scared you, this is the part where you would take out your credit card and give them $39.99 to clean your PC.

Don’t Believe the Hype

Temporary files are not slowing down your computer, and neither are browser history entries or cookies. Registry entries are generally not a problem — there’s a reason Microsoft once created a registry cleaner of their own before discontinuing it and advising people not to use registry cleaners.

Yes, your computer can be slow because its file system is fragmented. You can fix this by running the Disk Defragmenter tool included with Windows — the Disk Defragmenter runs automatically on a schedule, anyway. Most people shouldn’t have to worry about defragmenting their hard drives anymore.

How to Actually Clean Your PC

Let’s say you want to clean your PC just like a PC cleaner would. Here’s what you can do:

Run the Disk Cleanup tool included with Windows. It’s focused on freeing up space on your hard drive, but it will also delete old temporary files and other useless things. Just tap the Windows key, type Disk Cleanup, and press Enter to launch it. You can even schedule a Disk Cleanup to clean your computer automatically. Clear your browser history or — even better — set your browser to automatically clear its history when you close it if you don’t want to store a history. Run the Disk Defragmenter included with Windows. This isn’t necessary if you use a solid-state drive. Don’t bother with a registry cleaner. If you must, use the free CCleaner, which has the best-tested registry cleaner out there. It will also delete temporary files for other programs — CCleaner alone does much more than these PC cleaning apps do.

A test performed in 2011 by Windows Secrets found that the Disk Cleanup tool included with Windows was just as good as paid PC cleaning apps. Note that this is true even though PC cleaning apps fix “registry errors” while the Disk Cleanup app doesn’t, which shows just how unnecessary registry cleaners are.

So yes, it’s been tested — PC cleaning apps are worthless.

Speeding Up Your Computer

The best tools for speeding up your computer are things that a PC cleanup app won’t do for you:

Uninstall software you no longer use, especially programs that run at startup and browser plug-ins. Disable unnecessary startup apps to improve Windows’ boot time.

If you regularly see errors on your computer:

Run an antivirus program and an antimalware program to scan your computer for malware-producing error messages. Google error messages you see regularly to find fixes for them.

Don’t forget the nuclear option:

Reinstall Windows to start over from a clean slate. If you’re using Windows 8, use the Refresh Your PC feature. Check for hardware problems if you continue to experience blue screens or other PC problems after reinstalling Windows.

At worst, PC cleaning apps are digital snake oil. At best, they do a few marginally useful things that you can do with tools included with Windows. Don’t believe the hype — skip the PC cleaning apps.