markdown-lint-mcp

A Model Context Protocol (MCP) server for markdown linting, formatting, and compliance checking.

Overview

This MCP server provides AI assistants with the ability to lint, validate, and auto-fix Markdown files to ensure compliance with established Markdown standards and best practices.

The Problem

While many MCP servers exist for converting various file formats to Markdown, there was no MCP server specifically designed for linting and ensuring compliance of existing Markdown files. This creates a gap in the workflow where Markdown content may be created or converted but not validated for quality and consistency.

Solution

markdown-lint-mcp bridges this gap by providing:

• Markdown linting using industry-standard rules
• Automatic fixing of common Markdown issues
• Compliance validation against established standards
• Seamless integration with MCP-compatible AI assistants

Features

MCP Tools Provided

1. lint_markdown - Analyze a Markdown file and return detailed issues
2. fix_markdown - Automatically fix Markdown issues and return corrected content
3. get_configuration - Display current linting rules and configuration

Standards-Based Approach

• Uses markdownlint default ruleset (community standard)
• Based on CommonMark specification
• Follows GitHub Flavored Markdown conventions
• Supports all 52 official markdownlint rules

Auto-Fixable Rules

Our MCP server can automatically fix 30 out of 52 official markdownlint rules (58%). These rules are deterministic and can be fixed without human judgment:

Whitespace & Formatting (9 rules)

• MD009 - Trailing spaces
• MD010 - Hard tabs
• MD012 - Multiple consecutive blank lines
• MD022 - Headings surrounded by blank lines
• MD031 - Fenced code blocks surrounded by blank lines
• MD032 - Lists surrounded by blank lines
• MD047 - Files should end with single newline
• MD058 - Tables surrounded by blank lines
• MD027 - Multiple spaces after blockquote symbol

Heading Formatting (6 rules)

• MD018 - No space after hash
• MD019 - Multiple spaces after hash
• MD020 - No space inside closed ATX
• MD021 - Multiple spaces inside closed ATX
• MD023 - Headings start at line beginning
• MD026 - Trailing punctuation in heading

List Formatting (4 rules)

• MD004 - Unordered list style
• MD005 - List item indentation consistency
• MD007 - Unordered list indentation
• MD030 - Spaces after list markers

Link & Text Formatting (7 rules)

• MD011 - Reversed link syntax
• MD034 - Bare URL used
• MD037 - Spaces inside emphasis
• MD038 - Spaces inside code spans
• MD039 - Spaces inside link text
• MD049 - Emphasis style
• MD050 - Strong style

Advanced Fixable (4 rules)

• MD014 - Dollar signs before commands
• MD044 - Proper names capitalization
• MD051 - Link fragments validation
• MD053 - Unused reference definitions

Detection-Only Rules

The following 22 rules (42%) cannot be automatically fixed because they require human judgment, content understanding, or style decisions:

Structural/Content Rules (12 rules)

• MD001 - Heading increment (requires understanding document structure)
• MD003 - Heading style consistency (needs style preference decision)
• MD013 - Line length (requires content-aware line breaking)
• MD024 - Duplicate headings (could break document structure/navigation)
• MD025 - Multiple H1s (requires understanding document hierarchy)
• MD028 - Blank line in blockquote (ambiguous semantic intent)
• MD029 - Ordered list numbering (style preference)
• MD035 - Horizontal rule style (style preference)
• MD036 - Emphasis as heading (requires semantic understanding)
• MD041 - First line H1 (may break existing document structure)
• MD043 - Required heading structure (document-specific requirements)
• MD046 - Code block style (style preference)

Content/Language Rules (5 rules)

• MD033 - Inline HTML (may be intentional/necessary)
• MD040 - Code language specification (requires code language knowledge)
• MD045 - Alt text for images (requires understanding image content)
• MD059 - Descriptive link text (requires understanding context/purpose)
• MD042 - Empty links (may be placeholders or templates)

Reference/Link Rules (3 rules)

• MD052 - Reference links defined (may be external or conditional)
• MD054 - Link/image style (style preference)
• MD056 - Table column count (may be intentional formatting)

Table Rules (2 rules)

• MD055 - Table pipe style (style preference)
• MD048 - Code fence style (style preference)

Installation

npm install @dougis/markdown-lint-mcp

Usage

With Claude Desktop

Add to your Claude Desktop MCP configuration:

{
  "mcpServers": {
    "markdownlint": {
	      "command": "npx",
	      "args": ["@dougis/markdown-lint-mcp"]
    }
  }
}

With Other MCP Clients

This server works with any MCP-compatible client including:

• Claude Desktop
• Cursor
• Cline
• VS Code with MCP support

Example Workflows

Lint a Markdown File

User: "Please lint my README.md file and tell me what issues exist"
AI: Uses lint_markdown tool to analyze and report issues

Fix Markdown Issues

User: "Fix all the markdown issues in my documentation files"
AI: Uses fix_markdown tool to automatically correct problems

Validate Compliance

User: "Is my markdown compliant with standard formatting rules?"
AI: Uses lint_markdown to validate and provide compliance status

Technical Approach

• Direct library integration with markdownlint npm package
• No external CLI dependencies required
• Cross-platform support (Windows, macOS, Linux)
• Single installation - no additional tools needed
• Efficient processing via direct API calls

Development Status

🚀 Production Ready - This project has reached a high level of maturity with:

1. ✅ Complete MCP server implementation with all 52 markdownlint rules
2. ✅ Comprehensive testing suite - 82% coverage (42/51 rules with full tests)
3. ✅ 522 passing tests with 100% success rate
4. ✅ All Priority 1 rules fully tested (11/11 critical rules)
5. 🔄 Final testing phase for remaining specialized rules
6. 📋 Ready for community testing and feedback

Testing Coverage Status

Our test suite demonstrates production quality with extensive validation:

• ✅ 19 test suites all passing
• ✅ 522 total tests with 0 failures
• ✅ 82% rule coverage (42 out of 51 rules fully tested)
• ✅ 100% Priority 1 rules tested (all critical functionality)
• ✅ Detection and fix validation for all tested rules
• ✅ Edge case and configuration testing implemented

Remaining Work (8% of rules)

Only 9 specialized rules remain to be tested:

• MD039, MD050, MD051, MD052, MD053, MD054 - Link and styling rules
• Integration testing for rule combinations
• Performance testing with large files

Contributing

We welcome contributions! This project follows MCP best practices and maintains high code quality standards.

Roadmap

• [x] ✅ Core MCP server implementation
• [x] ✅ Comprehensive testing suite (82% complete)
• [x] ✅ Production-quality code with 522 passing tests
• [ ] 🔄 Complete remaining 9 rules testing
• [ ] 📚 Enhanced documentation and examples
• [ ] 🤝 Community feedback integration
• [ ] 📦 Submission to official MCP collection

License

MIT License - see LICENSE file for details

Related Projects

• markdownlint - The underlying linting engine
• Model Context Protocol - The protocol this server implements
• MCP Servers Collection - Official MCP servers

Support

For issues, questions, or contributions, please use the GitHub issues page.