What is an .key file?
An .key file is a presentation created in Apple Keynote, part of Apple's iWork suite (the rival to Microsoft PowerPoint). It uses a proprietary format that Windows, Android, Chromebook and Linux can't read natively, which is why the file often shows up as an unknown type or opens as gibberish.
Under the hood, an .key file is actually a ZIP package with a ready-made PDF preview inside. Every tool linked on this page uses that fact to open the file locally in your browser - instantly and privately, with no upload and no conversion server.
Open, view or convert - which do you need?
If you just want to read the presentation once, use an online viewer - it shows the content and lets you download a PDF. If the file won't open on a specific device, use the "open on {your platform}" guide, which walks through that exact case. If you need an editable copy, use a converter to turn it into PDF or PowerPoint format.
All three routes use the same private, in-browser engine. Pick whichever matches your goal from the links below - they're grouped by open, view and convert.