Upgrading to Windows 10 is relatively easy, but reinstalling it might pose a few problems, especially if you don’t have your product key available.

There are plenty of free tools around which can display product keys for Windows XP, 7, 8, but what happens if you try them on Windows 10? We took a look.

Magical Jelly Bean Keyfinder is a popular choice. The installer is a hassle – you’ll need to opt for a custom installation and clear a checkbox to avoid the adware – but just run it and you get the Windows edition (10 Home in our test case), CD key, computer name and registered owner.

There’s a small issue in that the “Product Part No” looks garbled, but the Keyfinder version we tried (2.0.10.11) doesn’t claim to fully support Windows 10, and the program correctly told us everything that matters.

ProduKey showed both our current product key, and the last one

SterJo Key Finder is portable, so less hassle to use, and doesn’t display as much information. But it correctly displayed the key, and that’s what matters.

NirSoft’s ProduKey is an old favourite of ours, and right now its web page doesn’t mention Windows 10 support. So, would it deliver?

Of course. NirSoft always delivers. And actually, it gave us more information than anyone else. Not only did it display our Windows 10 edition, product ID and key, it also listed “Internet Explorer” as a separate product, along with the key from our previous Windows version (we’d upgraded from 7). We’re not sure how much use that information will actually be, but it’s there if you need it.

Most product key finders seem to have no major problems with Windows 10, it seems, but for its portability, extra features (including support for Office and some other products) and lack of adware, ProduKey would be our pick.