open-devtools

All-in-one MCP server providing LSP diagnostics, linting, and code formatting for AI coding assistants.

What is this?

open-devtools is a comprehensive Model Context Protocol (MCP) server that brings professional developer tooling to AI assistants like Claude Desktop, Cline, and other MCP-compatible applications. It combines:

• LSP Diagnostics - Real-time errors, warnings, and hints from language servers
• Linting - Code quality checks via ESLint, Biome, and other linters
• Formatting - Auto-format code with industry-standard tools

Features

• 🔍 9 LSP Servers - ESLint, Biome, TypeScript, Python, Go, Ruby, Rust, C#, Java
• 🎨 11 Formatters - Prettier, Biome, gofmt, ruff, rubocop, clang-format, and more
• ⚡ 40+ File Extensions - Support for all major programming languages
• 🚀 Zero Configuration - Works out of the box with auto-detection
• ⚙️ Fully Configurable - Customize servers, formatters, and file extensions
• 🔧 3 MCP Tools - get_diagnostics, format_file, lint_file

Supported Languages

LSP Servers (Diagnostics & Linting)

| Language | Server | Extensions | Features | |----------|--------|------------|----------| | JavaScript/TypeScript | ESLint | .js, .jsx, .ts, .tsx, .vue, .mjs, .cjs | Linting, code quality | | JavaScript/TypeScript/JSON | Biome | .js, .jsx, .ts, .tsx, .json, .jsonc | Fast linting & formatting | | TypeScript/JavaScript | TypeScript | .ts, .tsx, .js, .jsx, .mjs, .cjs, .mts, .cts | Type checking, intellisense | | Python | Pyright | .py, .pyi | Type checking, imports | | Go | gopls | .go | Go tooling | | Ruby | ruby-lsp | .rb, .rake | Ruby analysis | | Rust | rust-analyzer | .rs | Rust diagnostics | | C# | OmniSharp | .cs | C# analysis | | Java | JDTLS | .java | Java diagnostics |

Formatters

| Formatter | Languages | Extensions | |-----------|-----------|------------| | Prettier | JS/TS, HTML, CSS, Markdown, JSON, YAML | 20+ extensions | | Biome | JS/TS, JSON | Same as Prettier | | gofmt | Go | .go | | ruff | Python | .py, .pyi | | rubocop | Ruby | .rb, .rake, .gemspec, .ru | | standardrb | Ruby | .rb, .rake, .gemspec, .ru | | clang-format | C/C++ | .c, .cpp, .h, etc. | | ktlint | Kotlin | .kt, .kts | | zig fmt | Zig | .zig, .zon | | mix format | Elixir | .ex, .exs, etc. | | htmlbeautifier | ERB/HTML | .erb, .html.erb |

Installation

Prerequisites

Bun Runtime Required: This package uses Bun as its runtime. Install it first:

curl -fsSL https://bun.sh/install | bash

Important: The MCP server does not auto-install dependencies. You must manually install the language servers and formatters you need.

Auto-installed (via bunx): The following tools download automatically on first use:

• ESLint language server (requires ESLint installed in your project)
• TypeScript language server
• Biome language server and formatter (formatter requires biome.json config)
• Prettier formatter (requires Prettier in your project's package.json)

Install other tools you'll use:

# JavaScript/TypeScript - install in your project for ESLint/Prettier to work
npm install --save-dev eslint prettier

# Python  
pip install pyright ruff

# Go
go install golang.org/x/tools/gopls@latest

# Ruby
gem install ruby-lsp rubocop standardrb

# Rust
rustup component add rust-analyzer

# C/C++, Kotlin, Zig, Elixir (install as needed)
# See language-specific documentation

Using with Claude Desktop

Add to your Claude Desktop configuration:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "open-devtools": {
      "command": "bunx",
      "args": ["--bun", "open-devtools"]
    }
  }
}

Note: This package requires Bun runtime. If you don't have Bun installed, run: curl -fsSL https://bun.sh/install | bash

Using with Cline (VS Code)

{
  "mcpServers": {
    "open-devtools": {
      "command": "bunx",
      "args": ["--bun", "open-devtools"]
    }
  }
}

Using with Amp

{
  "amp.mcpServers": {
    "open-devtools": {
      "command": "bunx",
      "args": ["--bun", "open-devtools"]
    }
  }
}

Available Tools

get_diagnostics

Get LSP diagnostics (errors, warnings, hints) for a file. Automatically starts the appropriate language server if needed.

Parameters:

• filePath (string, required) - Absolute path to the file

Example:

Diagnostics for /path/to/file.ts:

ERROR [10:5] Cannot find name 'foo'
WARN [15:12] 'bar' is declared but never used
INFO [20:1] File is a CommonJS module

format_file

Format a file using the appropriate formatter. Automatically detects the formatter based on file extension and project configuration.

Parameters:

• filePath (string, required) - Absolute path to the file

Example:

Successfully formatted /path/to/file.ts using prettier

lint_file

Get linting information for a file.

Note: Most linting is handled by LSP servers through get_diagnostics (ESLint, Biome, etc.). Use get_diagnostics for comprehensive linting diagnostics.

Configuration

Configure LSP servers and formatters using environment variables:

{
  "mcpServers": {
    "open-devtools": {
      "command": "npx",
      "args": ["-y", "open-devtools"],
      "env": {
        "OPEN_DEVTOOLS_LSP_CONFIG": "{\"eslint\":{\"disabled\":false}}",
        "OPEN_DEVTOOLS_FORMATTER_CONFIG": "{\"prettier\":{\"disabled\":false}}"
      }
    }
  }
}

LSP Configuration Structure

{
  "server-name": {
    "disabled": false,           // Set to true to disable
    "command": ["cmd", "args"],  // Override command
    "extensions": [".ext"],      // Override file extensions
    "env": {                     // Environment variables
      "VAR": "value"
    },
    "initialization": {}         // LSP initialization options
  }
}

Formatter Configuration Structure

{
  "formatter-name": {
    "disabled": false,              // Set to true to disable
    "command": ["cmd", "$FILE"],    // Override command ($FILE placeholder)
    "extensions": [".ext"],         // Override file extensions
    "environment": {                // Environment variables
      "VAR": "value"
    }
  }
}

Available Server and Formatter Names

LSP Servers:

• eslint - JavaScript/TypeScript linting
• biome - Fast JS/TS/JSON linting & formatting
• typescript - TypeScript type checking
• pyright - Python type checking
• gopls - Go language server
• ruby-lsp - Ruby language server
• rust-analyzer - Rust language server
• omnisharp - C# language server
• jdtls - Java language server

Formatters:

• prettier - Multi-language formatter
• biome - Fast JS/TS/JSON formatter
• gofmt - Go formatter
• ruff - Python formatter
• rubocop - Ruby formatter with auto-correct
• standardrb - Ruby standard style formatter
• clang-format - C/C++ formatter
• ktlint - Kotlin formatter
• zig - Zig formatter
• mix - Elixir formatter
• htmlbeautifier - ERB/HTML formatter

Configuration Examples

Disable Built-in Servers/Formatters

{
  "mcpServers": {
    "open-devtools": {
      "command": "npx",
      "args": ["-y", "open-devtools"],
      "env": {
        "OPEN_DEVTOOLS_LSP_CONFIG": "{\"typescript\":{\"disabled\":true}}",
        "OPEN_DEVTOOLS_FORMATTER_CONFIG": "{\"prettier\":{\"disabled\":true}}"
      }
    }
  }
}

Override File Extensions

{
  "env": {
    "OPEN_DEVTOOLS_LSP_CONFIG": "{\"biome\":{\"extensions\":[\".ts\",\".tsx\",\".js\"]}}",
    "OPEN_DEVTOOLS_FORMATTER_CONFIG": "{\"prettier\":{\"extensions\":[\".js\",\".ts\"]}}"
  }
}

Add Custom LSP Server

{
  "env": {
    "OPEN_DEVTOOLS_LSP_CONFIG": "{\"lua-lsp\":{\"command\":[\"lua-language-server\",\"--stdio\"],\"extensions\":[\".lua\"]}}"
  }
}

Add Custom Formatter

{
  "env": {
    "OPEN_DEVTOOLS_FORMATTER_CONFIG": "{\"stylua\":{\"command\":[\"stylua\",\"$FILE\"],\"extensions\":[\".lua\"]}}"
  }
}

Configure with Environment Variables

{
  "env": {
    "OPEN_DEVTOOLS_LSP_CONFIG": "{\"eslint\":{\"env\":{\"NODE_ENV\":\"development\"}}}"
  }
}

Multiple Configurations

{
  "env": {
    "OPEN_DEVTOOLS_LSP_CONFIG": "{\"typescript\":{\"disabled\":true},\"pyright\":{\"disabled\":true},\"eslint\":{\"env\":{\"DEBUG\":\"true\"}}}"
  }
}

How It Works

1. Auto-Detection: Detects language servers and formatters based on file extension and project configuration
2. Smart Caching: Reuses language server instances across multiple requests to the same project
3. Project-Aware: Finds project roots (e.g., package.json, tsconfig.json, go.mod) automatically
4. Config-Driven: Respects your project's formatter configs (.prettierrc, biome.json, etc.)

Troubleshooting

No diagnostics/linting

• Ensure the language server is installed (which typescript-language-server, etc.)
• Check that your file is part of a valid project
• Some servers require config files (e.g., tsconfig.json for TypeScript)

Formatter not found

Install the formatter for your language. See Installation.

ESLint not working

• Install ESLint language server: npm install -g vscode-eslint-language-server
• Ensure ESLint is configured in your project (.eslintrc.* or eslint.config.js)
• Make sure ESLint is installed in your project: npm install --save-dev eslint

Contributing

Contributions are welcome! Please follow these steps:

1. Fork the repository: https://github.com/thenamankumar/open-devtools
2. Create a feature branch: git checkout -b feature/your-feature
3. Make your changes and add tests
4. Run tests: bun test
5. Run typecheck: bun run typecheck
6. Commit your changes: git commit -am 'Add some feature'
7. Push to the branch: git push origin feature/your-feature
8. Submit a pull request

Development Setup

# Clone the repository
git clone https://github.com/thenamankumar/open-devtools.git
cd open-devtools

# Install dependencies
bun install

# Run tests
bun test

# Run typecheck
bun run typecheck

# Run in development mode
bun run dev

Adding New LSP Servers or Formatters

Use the configuration system to test custom servers/formatters before submitting a PR. See the Configuration section for examples.

Issues & Support

• Bug Reports: GitHub Issues
• Feature Requests: GitHub Issues
• Discussions: GitHub Discussions

License

MIT License - see LICENSE file for details

Copyright (c) 2025 Naman Kumar

Related Projects

• Model Context Protocol - Protocol specification
• MCP Servers - Official MCP servers collection

Acknowledgments

This project combines functionality from various language servers and formatters. Thanks to all the maintainers of:

• TypeScript, ESLint, Biome, Prettier
• Pyright, gopls, rust-analyzer, ruby-lsp
• And all other tools integrated into this server

Star ⭐ this repo if you find it useful!