They're not really the same kind of thing. LSP is a carrier format, but it doesn't know or care how you parse things, whether it's with PEGs or an earley parser or shift reduce or whatever

https://janetdocs.org/ does (server side) syntax highlighting through hiccup-lexer which converts janet-peg's tokens to hiccup: https://github.com/sogaiu/janet-peg

The LSP used on vscode works with PEGs also: https://github.com/CFiggers/janet-lsp/blob/ca526aee35c60bcf5...