Amazon seems to be rolling out a new "Part Finder" tool to check the compatibility of PC parts. On some PC component product pages, a widget at the top lets you select the brand and model number of your existing rig to check if the part is compatible.
The system appears to be brand new, and only shows up on some part pages—I saw it on this listing for a Samsung 860 Evo SSD, for example, but not an MSI GTX 1080. From what I can tell, Part Finder isn't as full-featured as tools like PC Part Picker's Compatibility Check, and it only works for systems that actually have a model number—prebuilts and laptops, that is. This means it's no use if you built your rig yourself, though you can at least check if two specific parts will match up, like a set of RAM sticks and a particular motherboard.
The system is definitely in its early days, and it'll only be useful if it actually builds its knowledge base to a more complete level. As it stands, if you're building your own PC, you're much better off checking your parts on PC Part Picker—or following one of our build guides—than relying on Amazon's budding system. But if nothing else, it'll be a useful tool for folks who started off with a prebuilt rig and are now looking for their next upgrade. Might I suggest an SSD?