So you're saying the LSP portion checks the file(s) you're currently editing, whereas the watchman (also incremental) check or the non-incremental check do the whole project?

Edit: for the active file / LSP part, I mean it shows errors mainly for the active file.

Exactly - the LSP portion of pyre works for files you have open in an editor, but might miss changes due to a rebase or files you edit on the terminal. The watchman integration is there to make sure that pyre's aware of changes outside your editor.

Edit: pyre will show type errors for all files in your repository, not just the ones you have open.

Ah, that's nice. So you can change the type of a function in one file that you are editing, and pyre will show you all the other places that are now using the wrong types.