Simple LSP Client

A minimal VS Code extension that starts configured stdio language servers and stdin/stdout formatters.

Configuration

Configure simpleLspClient.servers as an object keyed by server name:

{
  "simpleLspClient.servers": {
    "ruff": {
      "cmd": ["ruff", "server"],
      "filetypes": ["python"]
    }
  }
}

Configure simpleLspClient.formatters the same way for stdin/stdout formatters:

{
  "simpleLspClient.formatters": {
    "prettier": {
      "cmd": ["prettier", "--stdin-filepath", "${file}"],
      "filetypes": ["javascript", "typescript"]
    }
  }
}

Each server and formatter supports:

• cmd: exact command and arguments to run.
• filetypes: VS Code language IDs to attach to.
• env: optional environment variables for the process.

Servers also support:

• initializationOptions: optional JSON value passed in the LSP initialize request.

Global formatter setting:

• simpleLspClient.formatterTimeoutMs: formatter timeout in milliseconds. Defaults to 30000; set to 0 to disable.

The extension does not add transport flags like --stdio. Put only the arguments your server expects in cmd.

Server cmd entries and env values support these variables:

• ${workspaceFolder}
• ${workspaceFolderBasename}
• ${cwd}
• ${userHome}
• ${pathSeparator}
• ${execPath}

Formatter cmd entries and env values support those variables plus:

• ${file}
• ${relativeFile}
• ${filetype}

Formatters always receive document text on stdin and must write formatted text to stdout. Unlike LSP clients, formatters are registered by language ID without restricting the document URI scheme.

Server and formatter processes also receive matching SIMPLE_LSP_CLIENT_* environment variables for the workspace, cwd, user home, path separator, and VS Code executable path. Workspace environment values are empty when no workspace is open.

When a workspace is open, server processes use the first workspace folder as their working directory.

Examples

{
  "simpleLspClient.servers": {
    "ruff": {
      "cmd": ["ruff", "server"],
      "filetypes": ["python"]
    },
    "basedpyright": {
      "cmd": ["basedpyright-langserver", "--stdio"],
      "filetypes": ["python"]
    },
    "clangd": {
      "cmd": ["clangd"],
      "filetypes": ["c", "cpp", "objective-c", "objective-cpp"]
    }
  },
  "simpleLspClient.formatters": {
    "prettier": {
      "cmd": ["prettier", "--stdin-filepath", "${file}"],
      "filetypes": ["javascript", "typescript", "json", "markdown"]
    },
    "clang-format": {
      "cmd": ["clang-format", "--assume-filename", "${file}"],
      "filetypes": ["c", "cpp", "objective-c", "objective-cpp"]
    }
  }
}

Example with environment and initialization options:

{
  "simpleLspClient.servers": {
    "custom": {
      "cmd": ["custom-language-server"],
      "filetypes": ["custom"],
      "env": {
        "CUSTOM_SDK": "/opt/custom-sdk"
      },
      "initializationOptions": {
        "indexWorkspace": true
      }
    }
  }
}

Commands

• Simple LSP Client: Restart Servers
• Simple LSP Client: Show Status
• Simple LSP Client: List Configured Servers
• Simple LSP Client: List Configured Formatters
• Simple LSP Client: List Variables

Behavior

• Servers start when a matching document is already open or later opened.
• Servers stay running after matching documents close.
• The first workspace folder is used as the server process working directory.
• cmd entries and env values expand the documented placeholders.
• Formatters are killed if they exceed simpleLspClient.formatterTimeoutMs.
• Only stdio language servers are supported.

Manual Test Checklist

• Open a Python file with Ruff configured as ["ruff", "server"]; confirm diagnostics or formatting work.
• Open a Python file with both Ruff and basedpyright configured; confirm both clients appear in Show Status.
• Open a C or C++ file with clangd configured; confirm hover, completion, diagnostics, or formatting work.
• Configure only a formatter for jsonc; confirm VS Code offers it for Format Document.
• Change simpleLspClient.servers or simpleLspClient.formatters; confirm reload behavior in the output channel.
• Run Simple LSP Client: List Variables; confirm workspace variables resolve as expected.

Build

make vsix

See examples/settings.json for a multi-server setup.