VSCode LSP MCP

🔍 Overview

VSCode LSP MCP is a Visual Studio Code extension that exposes Language Server Protocol (LSP) features through the Model Context Protocol (MCP).

Extension ID: cjl.lsp-mcp — open Extensions (Ctrl+Shift+X / Cmd+Shift+X) and search for cjl.lsp-mcp to find this plugin precisely.

This allows AI assistants and external tools to utilize VSCode's powerful language intelligence capabilities without direct integration.

vscode-ext demo

🌟 Why This Extension?

Large language models like Claude and Cursor struggle to understand your codebase accurately because:

They rely on regex patterns to find symbols, leading to false matches
They can't analyze import/export relationships properly
They don't understand type hierarchies or inheritance
They have limited code navigation capabilities

This extension bridges that gap, providing AI tools with the same code intelligence that VSCode uses internally!

⚙️ Features

🔄 LSP Bridge: Converts LSP features into MCP tools
🔌 Multi-Instance Support: Automatically handles port conflicts for multiple VSCode windows
🧠 16 LSP operations covering navigation (definition, declaration, implementation, references), documentation (hover, completions), structure (document/workspace symbols, call hierarchy), and manipulation (rename)
☕ Java dependency source: Get decompiled Java class source via jdt:// URI (from jdtls), so AI can read library implementations
📄 Dual output format: JSON for machine processing, Markdown for LLM-friendly reading

🛠️ Exposed MCP Tools

Operation	Description
`hover`	Get hover information (documentation, type, etc.) at a position
`definition`	Get the definition location of a symbol
`declaration`	Get the declaration location of a symbol
`implementation`	Get the implementation location(s) of a symbol
`references`	Find all references to a symbol
`completions`	Get intelligent code completion suggestions
`document_symbols`	Get the symbol outline (tree) of a document
`workspace_symbols`	Search for symbols across the entire workspace by query
`class_file_contents`	Get decompiled Java class source via jdt:// URI (from jdtls), to read library/dependency implementations
`rename`	Rename a symbol across the workspace
`symbol_at_position`	Get symbol metadata (name, kind, range) at a position
`incoming_calls`	Find all callers of a symbol
`outgoing_calls`	Find all callees (calls made by) a symbol

All operations are invoked through the single execute_lsp MCP tool with a unified input format:

operation — which LSP operation to execute
uri — file path or URI string (supports both plain paths and file:///jdt:// URIs)
line — line number (1-based, matching editor display). Required for position-dependent operations
character — character offset (1-based, matching editor display). Required for position-dependent operations
newName — required only for rename
query — required only for workspace_symbols

1-based positions: Both input and output use 1-based line/character values, matching what your editor displays. VS Code shows Ln 9, Col 16 → pass line: 9, character: 16. Output positions can be used directly as input for the next call — no conversion needed.

📋 Configuration

Key	Description	Type	Default
`lsp-mcp.enabled`	Enable or disable the LSP MCP server.	`boolean`	`true`
`lsp-mcp.port`	Port for the LSP MCP server.	`number`	`9527`
`lsp-mcp.maxRetries`	Maximum number of port retry attempts when the default port is occupied.	`number`	`10`
`lsp-mcp.cors.enabled`	Enable or disable CORS (Cross-Origin Resource Sharing).	`boolean`	`true`
`lsp-mcp.cors.allowOrigins`	Allowed origins for CORS. Use `*` to allow all origins, or provide a comma-separated list of origins (e.g., `http://localhost:3000,http://localhost:5173`).	`string`	`*`
`lsp-mcp.cors.withCredentials`	Whether to allow credentials (cookies, authorization headers) in CORS requests.	`boolean`	`false`
`lsp-mcp.cors.exposeHeaders`	Headers that browsers are allowed to access. Provide a comma-separated list of headers (e.g., `Mcp-Session-Id`).	`string`	`Mcp-Session-Id`
`lsp-mcp.maxResults`	Maximum number of items returned for list-type results (completions, workspace_symbols, etc.). Prevents excessive token usage.	`number`	`200`
`lsp-mcp.outputFormat`	Output format for LSP operation results. `json` for machine-readable JSON, `markdown` for LLM-friendly Markdown.	`string`	`json`

🔗 Integration with AI Tools

Cursor

Config file: ~/.cursor/mcp.json (e.g. %USERPROFILE%\.cursor\mcp.json on Windows)

{
  "mcpServers": {
    "lsp": {
      "url": "http://127.0.0.1:9527/mcp"
    }
  }
}

OpenCode

Config file: ~/.config/opencode/opencode.jsonc

{
  "mcp": {
    "lsp-mcp": {
      "type": "remote",
      "url": "http://127.0.0.1:9527/mcp",
      "enabled": true
    }
  }
}

Claude Code

Config file: ~/.claude.json

{
  "mcpServers": {
    "lsp-mcp": {
      "type": "http",
      "url": "http://127.0.0.1:9527/mcp"
    }
  }
}

Gemini | IFlow

Config file: ~/.gemini/settings.json

{
  "mcpServers": {
    "lsp-mcp": {
      "type": "streamable-http",
      "httpUrl": "http://127.0.0.1:9527/mcp"
    }
  }
}

Codex

Config file: ~/.codex/config.toml

[mcp_servers.lsp-mcp]
url = "http://127.0.0.1:9527/mcp"

Roo Code

{
  "mcpServers": {
    "lsp": {
      "type": "streamable-http",
      "url": "http://127.0.0.1:9527/mcp",
      "disabled": false
    }
  }
}

💻 Development

Clone the repository
Run pnpm install
Run pnpm run update to generate metadata
Press F5 to start debugging

LSP MCP

CJL