Language Server Protocol (LSP) client for Swift

What's New


  • Fix lifetime on server shutdown
  • Improved shutdown/exit handling

License Platforms Documentation


This is a Swift library for abstracting and interacting with language servers that implement the Language Server Protocol. It is built on top of the LanguageServerProtocol library.


Swift Package Manager

dependencies: [
    .package(url: "")



This class manages a locally-running LSP process.

let params = Process.ExecutionParameters(path: "/path/to/server-executable",
                                         arguments: [],
                                         environment: [])
let processServer = LocalProcessServer(executionParameters: params)
processServer.terminationHandler = { print("server exited") }

// and if you want to observe communications
processServer.logMessages = true

Setting correct environment variables could be critical for your server. Your program may not have the same environment as your shell. Capturing shell environment variables is tricky business. If you need help here, check out ProcessEnv.


Server wrapper that provides automatic initialization. This takes care of the protocol initialization handshake, and does so lazily, on first message.

import LanguageClient
import LanguageServerProtocol

let executionParams = Process.ExecutionParameters(path: "/usr/bin/sourcekit-lsp")

let localServer = LocalProcessServer(executionParameters: executionParams)

let config = InitializingServer.Configuration(initializeParamsProvider: {
    // you may need to fill in more of the textDocument field for completions
    // to work, depending on your server
    let capabilities = ClientCapabilities(workspace: nil,
                                          textDocument: nil,
                                          window: nil,
                                          general: nil,
                                          experimental: nil)
    // pay careful attention to rootPath/rootURI/workspaceFolders, as different servers will
    // have different expectations/requirements here
    return InitializeParams(processId: Int(ProcessInfo.processInfo.processIdentifier),
                            locale: nil,
                            rootPath: nil,
                            rootURI: projectURL.absoluteString,
                            initializationOptions: nil,
                            capabilities: capabilities,
                            trace: nil,
                            workspaceFolders: nil)
let server = InitializingServer(server: localServer, configuration: config)

let docURL = URL(fileURLWithPath: "/path/to/your/test.swift")
let projectURL = docURL.deletingLastPathComponent()

Task {
    let docContent = try String(contentsOf: docURL)

    let doc = TextDocumentItem(uri: docURL.absoluteString,
                               languageId: .swift,
                               version: 1,
                               text: docContent)
    let docParams = DidOpenTextDocumentParams(textDocument: doc)

    try await server.didOpenTextDocument(params: docParams)

    // make sure to pick a reasonable position within your test document
    let pos = Position(line: 5, character: 25)
    let completionParams = CompletionParams(uri: docURL.absoluteString,
                                            position: pos,
                                            triggerKind: .invoked,
                                            triggerCharacter: nil)
    let completions = try await server.completion(params: completionParams)

    print("completions: ", completions)


Server wrapper that provides transparent server-side state restoration should the underlying process crash.


A protocol useful for translating between NSRange and LSP's line-relative positioning system.


A utility class that uses FS events and glob patterns to handle DidChangeWatchedFiles.

Suggestions or Feedback

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Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.


  • Swift Tools 5.5.0
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Last updated: Sun Mar 12 2023 23:22:20 GMT-0500 (GMT-05:00)