Webp has been supported since last October, but type:webp never got added to the tag cheatsheet. All the other supported filetypes are there, so I figure webp probably should be too.
Topic: Add webp to the tag cheatsheet
Posted under Site Bug Reports & Feature Requests
...goddamnit... Thank you, it's there now.
maybe worth adding animated_webp the same way as animated_png as well?