Description

csharp-ls brings advanced language features like code completion, diagnostics, and refactoring to your editor for C# projects. It supports projects targeting older .NET SDK versions including .NET Core 3, .NET Framework 4.8, and potentially earlier ones.

csharp-ls is MIT-licensed (see LICENSE) and is provided with no warranty of any kind.

AI Assistance

This project has been developed with substantial help from LLMs, including the following models:

• anthropic/claude-opus-4-6
• anthropic/claude-sonnet-4-6
• anthropic/claude-sonnet-5

Source files carry an Assisted-by: header line per the Linux kernel coding-assistants convention.

Documentation

See CHANGELOG.md for the list of recent improvements/fixes.

See docs/features.md for a more detailed discussion regarding features and customization provided with csharp-ls.

See docs/troubleshooting.md for server troubleshooting and diagnostics.

See CONTRIBUTING.md for build instructions and codebase overview.

See docs/codebase-architecture.md for an overview of the project structure, LSP message handling, request scheduling, and test infrastructure.

Quick Start

csharp-ls requires the .NET 10 SDK or later to be installed on your machine. Please head to Download .NET to download it.

The server can be installed as csharp-ls dotnet tool:

dotnet tool install --global csharp-ls

Once installed, your editor's LSP client should automatically detect and start csharp-ls when opening C# project files.

Settings

Configuration

Settings are read from the csharp workspace configuration section (workspace/configuration) and can also be provided via workspace/didChangeConfiguration.

• csharp.logLevel - log level for server output forwarded via $/logTrace; one of trace, debug, info, warning, error; defaults to info

• csharp.applyFormattingOptions - use formatting options as supplied by the client (may override .editorconfig values); defaults to false

• csharp.analyzersEnabled - run Roslyn analyzers (e.g. IDE style rules, third-party NuGet analyzers) as part of diagnostics; increases diagnostic latency and CPU usage; defaults to false

• csharp.useMetadataUris - serve decompiled metadata and source-generated documents under csharp:/ URIs; defaults to false

• csharp.razorSupport - enable Razor (.cshtml) document support; defaults to false

• csharp.solutionPathOverride - override the solution path to load; useful for specifying an alternative solution when multiple exist in the workspace; can also be set via the --solution CLI flag; defaults to null

• csharp.locale - force the output language for diagnostics and messages, e.g. en-US or de; useful for consistent logs across different OS locales; overrides DOTNET_CLI_UI_LANGUAGE; defaults to the system locale

• csharp.debug.solutionLoadDelay - delay in milliseconds before loading the solution after the workspace is ready

• csharp.debug.debugMode - enable debug mode, which logs periodic request queue statistics; defaults to false

Command Line Arguments

USAGE: csharp-ls [--help] [--version] [--loglevel <level>] [--solution <solution>] [--locale <locale>] [--debug] [--diagnose] [--features <features>] [--rpclog <path>]

OPTIONS:

    --version, -v         display versioning information
    --loglevel, -l <level>
                          set log level, <trace|debug|info|warning|error>; default is `info`
    --solution, -s <solution>
                          specify .sln file to load (relative to CWD)
    --locale, -L <locale> force output locale, e.g. `en-US` or `de`; overrides DOTNET_CLI_UI_LANGUAGE
    --debug               enable debug mode
    --diagnose            run diagnostics
    --features, -f <features>
                          enable optional features, comma-separated: [metadata-uris, razor-support]
    --rpclog <path>       write RPC wire log to file (READ/WRITE/ERROR/...)
    --help                display this list of options.

See csharp-ls --help.

Environment Variables

• DOTNET_CLI_UI_LANGUAGE - sets the output locale for diagnostics and messages (e.g. en-US, de); follows the standard dotnet CLI convention; overridden by --locale / csharp.locale if set

LSP Tracing

csharp-ls supports the LSP $/setTrace and $/logTrace notifications. When a client sets tracing to messages or verbose, the server forwards its internal log output as $/logTrace notifications. This is independent of --loglevel, which only controls stderr console output. In VS Code, tracing can be enabled via the [langId].trace.server setting.

Extended Client Capabilities

Decompiled and Source-Generated Document URIs

When enabled, textDocument/definition on symbols in compiled assemblies or source-generated files returns a virtual csharp:/ URI instead of a temporary file path. The URI can then be passed to the custom csharp/metadata request to retrieve the decompiled or generated source text.

• Decompiled symbols: csharp:/<project.csproj>/decompiled/<Symbol>.cs
• Source-generated files: csharp:/<project.csproj>/generated/<HintName>

This can be enabled via the csharp.useMetadataUris configuration setting, the --features metadata-uris CLI flag, or by setting the experimental.csharp.metadataUris client capability to true.

Razor (.cshtml) support

Can be enabled via the csharp.razorSupport configuration setting or by passing the --features razor-support CLI flag.

Clients

csharp-ls implements the standard LSP protocol to interact with your editor. However, there are some features that require a non-standard implementation. This is where editor-specific plugins can be helpful.

Notable clients:

• Neovim: csharpls-extended-lsp.nvim
• Emacs: emacs/lsp-mode
• Emacs: eglot-csharp
• Visual Studio Code: vscode-csharp-ls @ github

Acknowledgements

• csharp-ls is not affiliated with Microsoft Corp.,
• csharp-ls uses Roslyn to parse and update code,
• csharp-ls uses the LSP interface from the Ionide.LanguageServerProtocol project,
• csharp-ls uses ILSpy/ICSharpCode.Decompiler to decompile types in assemblies to C# source.

Alternatives

• OmniSharp
• C# Dev Kit for VSCode