What is a language server? It’s a standard specification for an API that enables editors to implement intelligent editing behavior, like code completion, quality checks, or finding all the places a variable or function is used in your code.
The Language Server Protocol (LSP) defines the protocol used between an editor or IDE and a language server that provides language features like auto complete, go to definition, find all references etc. The goal of the Language Server Index Format (LSIF, pronounced like “else if”) is to support rich code navigation in development tools or a Web UI without needing a local copy of the source code.