languagetool-mcp-server

MCP server for the LanguageTool Pro API — brings spell-checking, grammar, and style suggestions directly into Claude Code and other MCP-compatible clients.

⚠️ LanguageTool Pro required — This server uses the LanguageTool Pro API. A paid LanguageTool Pro subscription with API access is required. The free tier does not provide API access.

📖 Deutsche Dokumentation

Prerequisites

• Node.js ≥ 18
• LanguageTool Pro account with API access (subscription required)
• API credentials: username (email address) + API key

Find your API key at: https://languagetool.org/editor/settings/access-tokens

Installation

Option A — via npx (no installation needed):

Use npx @dpesch/languagetool-mcp-server directly in your MCP config (see Setup below).

Option B — clone and build:

git clone https://codeberg.org/dpesch/languagetool-mcp-server
cd languagetool-mcp-server
npm install
npm run build

Credentials

The server reads credentials from environment variables:

| Variable | Description | |---------------|----------------------------------------------| | LT_USERNAME | LanguageTool username (email address) | | LT_API_KEY | API key from your account settings |

Setup in Claude Code (stdio — recommended for local use)

Add to ~/.claude/claude_desktop_config.json (Windows: %APPDATA%\Claude\claude_desktop_config.json):

Option A — via npx (recommended, no build step):

{
  "mcpServers": {
    "languagetool": {
      "command": "npx",
      "args": ["-y", "@dpesch/languagetool-mcp-server"],
      "env": {
        "LT_USERNAME": "[email protected]",
        "LT_API_KEY":  "your-api-key"
      }
    }
  }
}

Option B — local build:

{
  "mcpServers": {
    "languagetool": {
      "command": "node",
      "args": ["/path/to/languagetool-mcp-server/dist/index.js"],
      "env": {
        "LT_USERNAME": "[email protected]",
        "LT_API_KEY":  "your-api-key"
      }
    }
  }
}

Setup as HTTP server (for multiple clients)

[email protected] LT_API_KEY=your-key TRANSPORT=http PORT=3456 node dist/index.js

Then in your MCP configuration:

{
  "mcpServers": {
    "languagetool": {
      "type": "http",
      "url": "http://localhost:3456/mcp"
    }
  }
}

Health check: GET http://localhost:3456/health

Available Tools

lt_check_text

Full text check with categorized suggestions and corrections.

Parameters:

• text — text to check (max. 40,000 characters)
• language — language code (de-DE, en-US, …) or auto (default)
• picky — stricter checking with more style hints (default: false)
• disabled_rules — rule IDs to ignore
• enabled_rules — additional rule IDs to enable

lt_check_text_summary

Compact one-line summary without individual details — useful for quick checks.

lt_list_languages

All supported languages with language codes. Optionally filterable via filter parameter.

Categories

| Icon | Category | |------|----------------| | 🔴 | Spelling | | 🟠 | Grammar | | 🟡 | Punctuation | | 🔵 | Style | | ⚪ | Typography | | ⚫ | Other |

Development

# Watch mode
npm run dev

# Single build
npm run build

# Type check only
npm run typecheck

License

MIT © 2026 Dominik Pesch