> you're proposing plugin/cli -> lsp -> core Almost, to be exact it would be (plugin -> ((server -> core) / core)) and (cli -> core) > wasn't obvious whether LSP supported custom messages In primitive level, it's JSON RPC so I guess pretty much anything goes. The typescript implementation provided by MS has some generic handlers which probably can be used for this (haven't tried though). See e.g. https://github.com/microsoft/vscode-languageserver-node/blob/60a5a7825e6f54f57917091f394fd8db7d1724bc/server/src/common/server.ts#L1006 > are there advantages for doing file watching inside vscode isntead? Yes, see https://microsoft.github.io/language-server-protocol/specification#workspace_didChangeWatchedFiles