A keygen for Windows 10, Windows 8, or Windows 7 is a program that generates unique product keys for installing one of those versions of Windows, and they can be incredibly useful.
These versions of Windows, as well as other Microsoft operating systems, require unique and valid product keys during installation. In other words, you need a product key if you want to properly use Windows after you install it; you can't just install the OS and expect it to run normally.
Windows product keys, at least for these three newest versions of Windows, are 25 characters long, separated by a dash after every fifth character. Here's an example (this key isn't real):
Having a free, generated product key would save money if you're faced with buying a copy of Windows just for the key. It would also save lots of time, assuming you had a valid key but just lost it.
Windows Key Generators Usually Work With a Catch
Product key generators for popular versions of Windows usually work just fine to create a product key that your installation media sees as valid. However, it will not find your legal Windows product key.
No key generator for Windows is legal and, increasingly, no keygen will work to activate Windows. Just to be exceedingly clear: no product key for Windows 10, Windows 8, or Windows 7 that a keygen creates can legally be used.
There's a lot of information on this topic if you're willing to do some research, including how keygens work and why they're illegal in most countries.
So what do you do when you need a product key for Windows right now but realize a key generator isn't a good way to go?
Windows 10 Keygen Alternatives
Assuming you've just lost a previously purchased and valid Windows 10 key, you actually have several options.
The easiest, assuming Windows is still installed, is to use a free program called a key finder tool that will locate the key Windows 10 is using. We have an updated list of free product key finder programs with a lot of great choices.
Beyond that, you can sometimes request a new Windows 10 key by calling Microsoft, a process that isn't always successful but very much worth the try. If it works, you'll be happy you tried this.
Of course, you can always purchase a new copy of Windows 10 from Microsoft, but you might leave that as your last option for obvious reasons—$$.
Amazon sells copies of Windows 10, too, often times for less than what Microsoft charges.
Another option is to download Windows 10 free from Microsoft. You can use it free with only a few limitations; it doesn't render the computer completely useless. You'll just see a watermark on the desktop and a few customizations won't be able to be changed, but other than that, you can use an unactivated Windows 10 indefinitely.
These tips all work in general for Windows 8 as well, though Microsoft no longer sells Windows 8 directly. You can, however, download the Windows 8 ISO from Microsoft, but like Windows 10, this doesn't include a free product key.
Windows 7 Keygen Alternatives
Like with the Windows 10 (and Windows 8) discussion above, a Windows 7 keygen is just not a good option, especially considering that Microsoft has put many protections in place against Windows working properly with one of these generated product keys.
You may be able to locate your Windows 7 product key but it might require some patience. Many of those same key finder tools work for Windows 7—more, actually, because Microsoft didn't make it quite as hard to extract in this version of Windows.
If you know your product key but you're just in need of a Windows 7 disc, you can download Windows 7 free from Microsoft and use that to install or repair the OS. Unlike Windows 10, you do need a product key to get Windows 7 from Microsoft.
Requesting a new key is an option for Windows 7, too. Like with Windows 8, Microsoft no longer sells the OS, but there are probably copies floating around on Amazon and other online retailers like Newegg.