Language Server Protocol (LSP) Support

Qwen Code provides native Language Server Protocol (LSP) support, enabling advanced code intelligence features like go-to-definition, find references, diagnostics, and code actions. This integration allows the AI agent to understand your code more deeply and provide more accurate assistance.

Overview

LSP support in Qwen Code works by connecting to language servers that understand your code. When you work with TypeScript, Python, Go, or other supported languages, Qwen Code can automatically start the appropriate language server and use it to:

• Navigate to symbol definitions
• Find all references to a symbol
• Get hover information (documentation, type info)
• View diagnostic messages (errors, warnings)
• Access code actions (quick fixes, refactorings)
• Analyze call hierarchies

Quick Start

LSP is an experimental feature in Qwen Code. To enable it, use the --experimental-lsp command line flag:

qwen --experimental-lsp

For most common languages, Qwen Code will automatically detect and start the appropriate language server if it’s installed on your system.

Prerequisites

You need to have the language server for your programming language installed:

Configuration

.lsp.json File

You can configure language servers using a .lsp.json file in your project root. This uses the language-keyed format described in the Claude Code plugin LSP configuration reference .

Basic format:

{
  "typescript": {
    "command": "typescript-language-server",
    "args": ["--stdio"],
    "extensionToLanguage": {
      ".ts": "typescript",
      ".tsx": "typescriptreact",
      ".js": "javascript",
      ".jsx": "javascriptreact"
    }
  }
}

Configuration Options

Required Fields

Optional Fields

TCP/Socket Transport

For servers that use TCP or Unix socket transport:

{
  "remote-lsp": {
    "transport": "tcp",
    "socket": {
      "host": "127.0.0.1",
      "port": 9999
    },
    "extensionToLanguage": {
      ".custom": "custom"
    }
  }
}

Available LSP Operations

Qwen Code exposes LSP functionality through the unified lsp tool. Here are the available operations:

Code Navigation

Go to Definition

Find where a symbol is defined.

Operation: goToDefinition
Parameters:
  - filePath: Path to the file
  - line: Line number (1-based)
  - character: Column number (1-based)

Find References

Find all references to a symbol.

Operation: findReferences
Parameters:
  - filePath: Path to the file
  - line: Line number (1-based)
  - character: Column number (1-based)
  - includeDeclaration: Include the declaration itself (optional)

Go to Implementation

Find implementations of an interface or abstract method.

Operation: goToImplementation
Parameters:
  - filePath: Path to the file
  - line: Line number (1-based)
  - character: Column number (1-based)

Symbol Information

Hover

Get documentation and type information for a symbol.

Operation: hover
Parameters:
  - filePath: Path to the file
  - line: Line number (1-based)
  - character: Column number (1-based)

Document Symbols

Get all symbols in a document.

Operation: documentSymbol
Parameters:
  - filePath: Path to the file

Workspace Symbol Search

Search for symbols across the workspace.

Operation: workspaceSymbol
Parameters:
  - query: Search query string
  - limit: Maximum results (optional)

Call Hierarchy

Prepare Call Hierarchy

Get the call hierarchy item at a position.

Operation: prepareCallHierarchy
Parameters:
  - filePath: Path to the file
  - line: Line number (1-based)
  - character: Column number (1-based)

Incoming Calls

Find all functions that call the given function.

Operation: incomingCalls
Parameters:
  - callHierarchyItem: Item from prepareCallHierarchy

Outgoing Calls

Find all functions called by the given function.

Operation: outgoingCalls
Parameters:
  - callHierarchyItem: Item from prepareCallHierarchy

Diagnostics

File Diagnostics

Get diagnostic messages (errors, warnings) for a file.

Operation: diagnostics
Parameters:
  - filePath: Path to the file

Workspace Diagnostics

Get all diagnostic messages across the workspace.

Operation: workspaceDiagnostics
Parameters:
  - limit: Maximum results (optional)

Code Actions

Get Code Actions

Get available code actions (quick fixes, refactorings) at a location.

Operation: codeActions
Parameters:
  - filePath: Path to the file
  - line: Start line number (1-based)
  - character: Start column number (1-based)
  - endLine: End line number (optional, defaults to line)
  - endCharacter: End column (optional, defaults to character)
  - diagnostics: Diagnostics to get actions for (optional)
  - codeActionKinds: Filter by action kind (optional)

Code action kinds:

• quickfix - Quick fixes for errors/warnings
• refactor - Refactoring operations
• refactor.extract - Extract to function/variable
• refactor.inline - Inline function/variable
• source - Source code actions
• source.organizeImports - Organize imports
• source.fixAll - Fix all auto-fixable issues

Security

LSP servers are only started in trusted workspaces by default. This is because language servers run with your user permissions and can execute code.

Trust Controls

• Trusted Workspace: LSP servers start automatically
• Untrusted Workspace: LSP servers won’t start unless trustRequired: false is set in the server configuration

To mark a workspace as trusted, use the /trust command or configure trusted folders in settings.

Per-Server Trust Override

You can override trust requirements for specific servers in their configuration:

{
  "safe-server": {
    "command": "safe-language-server",
    "args": ["--stdio"],
    "trustRequired": false,
    "extensionToLanguage": {
      ".safe": "safe"
    }
  }
}

Troubleshooting

Server Not Starting

1. Check if the server is installed: Run the command manually to verify
2. Check the PATH: Ensure the server binary is in your system PATH
3. Check workspace trust: The workspace must be trusted for LSP
4. Check logs: Look for error messages in the console output
5. Verify —experimental-lsp flag: Make sure you’re using the flag when starting Qwen Code

Slow Performance

1. Large projects: Consider excluding node_modules and other large directories
2. Server timeout: Increase startupTimeout in server configuration for slow servers

No Results

1. Server not ready: The server may still be indexing
2. File not saved: Save your file for the server to pick up changes
3. Wrong language: Check if the correct server is running for your language

Debugging

Enable debug logging to see LSP communication:

DEBUG=lsp* qwen --experimental-lsp

Or check the LSP debugging guide at packages/cli/LSP_DEBUGGING_GUIDE.md.

Claude Code Compatibility

Qwen Code supports Claude Code-style .lsp.json configuration files in the language-keyed format defined in the Claude Code plugins reference . If you’re migrating from Claude Code, use the language-as-key layout in your configuration.

Configuration Format

The recommended format follows Claude Code’s specification:

{
  "go": {
    "command": "gopls",
    "args": ["serve"],
    "extensionToLanguage": {
      ".go": "go"
    }
  }
}

Claude Code LSP plugins can also supply lspServers in plugin.json (or a referenced .lsp.json). Qwen Code loads those configs when the extension is enabled, and they must use the same language-keyed format.

Best Practices

1. Install language servers globally: This ensures they’re available in all projects
2. Use project-specific settings: Configure server options per project when needed via .lsp.json
3. Keep servers updated: Update your language servers regularly for best results
4. Trust wisely: Only trust workspaces from trusted sources

FAQ

Q: How do I enable LSP?

Use the --experimental-lsp flag when starting Qwen Code:

qwen --experimental-lsp

Q: How do I know which language servers are running?

Use the /lsp status command to see all configured and running language servers.

Q: Can I use multiple language servers for the same file type?

Yes, but only one will be used for each operation. The first server that returns results wins.

Q: Does LSP work in sandbox mode?

LSP servers run outside the sandbox to access your code. They’re subject to workspace trust controls.