Language Server Protocol (LSP)
The Language Server Protocol (LSP) is an open, JSON-RPC-based standard that lets a development tool (the client) talk to a language-specific server to get features like go-to-definition, find-references, rename, autocomplete, and diagnostics. It decouples language intelligence from the editor, so one language server can power many editors.
LSP was introduced by Microsoft (originally for VS Code) and is now an open specification. Before it, every editor needed bespoke integration for every language, an M-by-N problem: M editors times N languages. LSP collapses that to M plus N. A language server understands one language deeply, and any LSP-speaking client can consume it. That is why a single rust-analyzer, gopls, or typescript-language-server works in VS Code, Neovim, Emacs, and Zed alike.
Communication runs over JSON-RPC, typically across stdio or a socket. The client sends requests like textDocument/definition, textDocument/references, textDocument/rename, and textDocument/hover; the server responds with locations, edits, or symbol information. The server also pushes notifications, most importantly textDocument/publishDiagnostics, which is how the squiggly errors and warnings appear in your editor. Capabilities are negotiated during an initialize handshake, so a client only uses features the server actually supports.
The key property for tooling is that LSP answers are semantic, not textual. A "find references" result is the set of places that actually resolve to the same symbol, accounting for scope, imports, and types, rather than a text match for the same name. A workspace rename returns a coordinated set of edits across files that keep the program compiling. This is the same machinery that powers IDE refactors.
Companion specifications extend the model: the Debug Adapter Protocol (DAP) does for debuggers what LSP does for language features, and the Build Server Protocol (BSP) covers build systems. Most mainstream languages now ship a maintained language server, and registries like Mason package hundreds of them for easy installation.