mcp-grammar-checker

A small MCP server that exposes LanguageTool's grammar and style checking as a tool, so an MCP client (Claude Code, Claude Desktop, or any other MCP-compatible host) can check text for issues directly.

Why

Built to give an AI coding assistant a real, tool-backed way to check grammar/style — rather than relying only on the model's own judgment — while learning MCP hands-on for a Solution Architect AI application.

Process note

First built by hand (directly against the official mcp SDK, discovering its current API by inspecting the installed package rather than following a tutorial). Later rebuilt against Anthropic's official mcp-server-dev:build-mcp-server skill's guided process, which confirmed the deployment choice (local stdio — this is a single-user personal tool, not something meant for distribution) but changed the framework: it recommends FastMCP 3.x (the fastmcp package on PyPI, by jlowin) for Python servers, not the frozen FastMCP 1.0 bundled inside the mcp SDK. This repo now reflects that second, guided pass.

Tool

check_grammar(text: str, language: str = "de-DE") -> str

Checks the given text using the public LanguageTool API and returns a formatted list of issues found (message, suggested replacements, surrounding context), or a confirmation that no issues were found.

Setup

Requires Python 3.12+ and uv.

git clone <this-repo>
cd mcp-grammar-checker
uv sync

Running standalone

uv run python server.py

The server communicates over stdio and expects to be launched by an MCP client, not run interactively.

Using with Claude Code / Claude Desktop

Add to your MCP config (e.g. .claude/settings.json or the Claude Desktop config file):

{
  "mcpServers": {
    "grammar-checker": {
      "command": "uv",
      "args": ["run", "--directory", "/absolute/path/to/mcp-grammar-checker", "python", "server.py"]
    }
  }
}

Restart the client, and the check_grammar tool will be available.

Notes

• Uses the public LanguageTool API (api.languagetool.org), which is rate-limited. For heavier use, LanguageTool can be self-hosted.
• Supports any language LanguageTool supports (e.g. en-US, de-DE, fr) via the language parameter.