rumdl 0.0.173

A fast Markdown linter written in Rust

rumdl - A high-performance Markdown linter, written in Rust

A modern Markdown linter and formatter, built for speed with Rust

| Docs | Rules | Configuration | vs markdownlint |

Quick Start

# Install using Cargo
cargo install rumdl

# Lint Markdown files in the current directory
rumdl check .

# Format files (exits 0 on success, even if unfixable violations remain)
rumdl fmt .

# Auto-fix and report unfixable violations (exits 1 if violations remain)
rumdl check --fix .

# Create a default configuration file
rumdl init

Overview

rumdl is a high-performance Markdown linter and formatter that helps ensure consistency and best practices in your Markdown files. Inspired by ruff 's approach to Python linting, rumdl brings similar speed and developer experience improvements to the Markdown ecosystem.

It offers:

• ⚡️ Built for speed with Rust - significantly faster than alternatives
• 🔍 54 lint rules covering common Markdown issues
• 🛠️ Automatic formatting with --fix for files and stdin/stdout
• 📦 Zero dependencies - single binary with no runtime requirements
• 🔧 Highly configurable with TOML-based config files
• 🌐 Multiple installation options - Rust, Python, standalone binaries
• 🐍 Installable via pip for Python users
• 📏 Modern CLI with detailed error reporting
• 🔄 CI/CD friendly with non-zero exit code on errors

Performance

rumdl is designed for speed. Benchmarked on the Rust Book repository (478 markdown files, October 2025):

With intelligent caching, subsequent runs are even faster - rumdl only re-lints files that have changed, making it ideal for watch mode and editor integration.

Table of Contents

• rumdl - A high-performance Markdown linter, written in Rust
  • A modern Markdown linter and formatter, built for speed with Rust
  • Quick Start
  • Overview
    • Performance
  • Table of Contents
  • Installation
    • Using Homebrew (macOS/Linux)
    • Using Cargo (Rust)
    • Using pip (Python)
    • Using uv
    • Using Nix (macOS/Linux)
    • Download binary
    • VS Code Extension
  • Usage
    • Stdin/Stdout Formatting
    • Editor Integration
  • Pre-commit Integration
    • Excluding Files in Pre-commit
  • CI/CD Integration
    • GitHub Actions
  • Rules
  • Command-line Interface
    • Commands
      • check [PATHS...]
      • fmt [PATHS...]
      • init [OPTIONS]
      • import <FILE> [OPTIONS]
      • rule [<rule>]
      • config [OPTIONS] [COMMAND]
      • server [OPTIONS]
      • vscode [OPTIONS]
      • version
    • Global Options
    • Exit Codes
    • Usage Examples
  • Configuration
    • Configuration Discovery
    • Editor Support (JSON Schema)
    • Global Configuration
    • Markdownlint Migration
    • Inline Configuration
    • Configuration File Example
    • Initializing Configuration
    • Configuration in pyproject.toml
    • Configuration Output
      • Effective Configuration (rumdl config)
      • Example output
    • Defaults Only (rumdl config --defaults)
  • Output Style
    • Output Format
      • Text Output (Default)
      • JSON Output
  • Development
    • Prerequisites
    • Building
    • Testing
    • JSON Schema Generation
  • License

Installation

Choose the installation method that works best for you:

Using Homebrew (macOS/Linux)

brew tap rvben/rumdl
brew install rumdl

Using Cargo (Rust)

cargo install rumdl

Using pip (Python)

pip install rumdl

Using uv

For faster installation and better dependency management with uv:

# Install directly
uv tool install rumdl

# Or run without installing
uv tool run rumdl check .

Using Nix (macOS/Linux)

nix-channel --update
nix-env --install --attr nixpkgs.rumdl

Alternatively, you can use flakes to run it without installation.

nix run --extra-experimental-features 'flakes nix-command' nixpkgs/nixpkgs-unstable#rumdl -- --version

Download binary

# Linux/macOS
curl -LsSf https://github.com/rvben/rumdl/releases/latest/download/rumdl-linux-x86_64.tar.gz | tar xzf - -C /usr/local/bin

# Windows PowerShell
Invoke-WebRequest -Uri "https://github.com/rvben/rumdl/releases/latest/download/rumdl-windows-x86_64.zip" -OutFile "rumdl.zip"
Expand-Archive -Path "rumdl.zip" -DestinationPath "$env:USERPROFILE\.rumdl"

VS Code Extension

For the best development experience, install the rumdl VS Code extension directly from the command line:

# Install the VS Code extension
rumdl vscode

# Check if the extension is installed
rumdl vscode --status

# Force reinstall the extension
rumdl vscode --force

The extension provides:

• 🔍 Real-time linting as you type
• 💡 Quick fixes for common issues
• 🎨 Code formatting on save
• 📋 Hover tooltips with rule documentation
• ⚡ Lightning-fast performance with zero lag

The CLI will automatically detect VS Code, Cursor, or Windsurf and install the appropriate extension. See the VS Code extension documentation for more details.

Usage

Getting started with rumdl is simple:

# Lint a single file
rumdl check README.md

# Lint all Markdown files in current directory and subdirectories
rumdl check .

# Format a specific file
rumdl fmt README.md

# Create a default configuration file
rumdl init

Common usage examples:

# Lint with custom configuration
rumdl check --config my-config.toml docs/

# Disable specific rules
rumdl check --disable MD013,MD033 README.md

# Enable only specific rules
rumdl check --enable MD001,MD003 README.md

# Exclude specific files/directories
rumdl check --exclude "node_modules,dist" .

# Include only specific files/directories
rumdl check --include "docs/*.md,README.md" .

# Watch mode for continuous linting
rumdl check --watch docs/

# Combine include and exclude patterns
rumdl check --include "docs/**/*.md" --exclude "docs/temp,docs/drafts" .

# Don't respect gitignore files (note: --respect-gitignore defaults to true)
rumdl check --respect-gitignore=false .

# Force exclude patterns even for explicitly specified files (useful for pre-commit)
rumdl check excluded.md --force-exclude  # Will respect exclude patterns in config

Stdin/Stdout Formatting

rumdl supports formatting via stdin/stdout, making it ideal for editor integrations and CI pipelines:

# Format content from stdin and output to stdout
cat README.md | rumdl fmt - > README_formatted.md
# Alternative: cat README.md | rumdl fmt --stdin > README_formatted.md

# Use in a pipeline
echo "# Title   " | rumdl fmt -
# Output: # Title

# Format clipboard content (macOS example)
pbpaste | rumdl fmt - | pbcopy

# Provide filename context for better error messages (useful for editor integrations)
cat README.md | rumdl check - --stdin-filename README.md

Editor Integration

For editor integration, use stdin/stdout mode with the --quiet flag to suppress diagnostic messages:

# Format selection in editor (example for vim)
:'<,'>!rumdl fmt - --quiet

# Format entire buffer
:%!rumdl fmt - --quiet

Pre-commit Integration

You can use rumdl as a pre-commit hook to check and fix your Markdown files.

The recommended way is to use the official pre-commit hook repository:

rumdl-pre-commit repository

Add the following to your .pre-commit-config.yaml:

repos:
  - repo: https://github.com/rvben/rumdl-pre-commit
    rev: v0.0.99  # Use the latest release tag
    hooks:
      - id: rumdl
        # To only check (default):
        # args: []
        # To automatically fix issues:
        # args: [--fix]

• By default, the hook will only check for issues.
• To automatically fix issues, add args: [--fix] to the hook configuration.

When you run pre-commit install or pre-commit run, pre-commit will automatically install rumdl in an isolated Python environment using pip. You do not need to install rumdl manually.

Excluding Files in Pre-commit

By default, when pre-commit passes files explicitly to rumdl, the exclude patterns in your .rumdl.toml configuration file are ignored. This is intentional behavior - if you explicitly specify a file, it gets checked.

However, for pre-commit workflows where you want to exclude certain files even when they're passed explicitly, you have two options:

1. Use force_exclude in your configuration file:

   # .rumdl.toml
   [global]
   exclude = ["generated/*.md", "vendor/**"]
   force_exclude = true  # Enforce excludes even for explicitly provided files
   

2. Use the --force-exclude flag in your pre-commit config:

   repos:
     - repo: https://github.com/rvben/rumdl-pre-commit
       rev: v0.0.99
       hooks:
         - id: rumdl
           args: [--force-exclude]  # Respect exclude patterns from config
   

CI/CD Integration

GitHub Actions

rumdl can output annotations directly in GitHub Actions format, making issues appear inline in pull requests:

- name: Lint Markdown
  run: rumdl check --output-format github .

This produces annotations that GitHub automatically displays in the PR's "Files changed" tab. Supports error/warning severity levels and precise issue locations.

Rules

rumdl implements 54 lint rules for Markdown files. Here are some key rule categories:

Category	Description	Example Rules
Headings	Proper heading structure and formatting	MD001, MD002, MD003
Lists	Consistent list formatting and structure	MD004, MD005, MD007
Whitespace	Proper spacing and line length	MD009, MD010, MD012
Code	Code block formatting and language tags	MD040, MD046, MD048
Links	Proper link and reference formatting	MD034, MD039, MD042
Images	Image alt text and references	MD045, MD052
Style	Consistent style across document	MD031, MD032, MD035

For a complete list of rules and their descriptions, see our documentation or run:

rumdl rule

Command-line Interface

rumdl <command> [options] [file or directory...]

Commands

check [PATHS...]

Lint Markdown files and print warnings/errors (main subcommand)

Arguments:

• [PATHS...]: Files or directories to lint. If provided, these paths take precedence over include patterns

Options:

• -f, --fix: Automatically fix issues where possible
• --diff: Show diff of what would be fixed instead of fixing files
• -w, --watch: Run in watch mode by re-running whenever files change
• -l, --list-rules: List all available rules
• -d, --disable <rules>: Disable specific rules (comma-separated)
• -e, --enable <rules>: Enable only specific rules (comma-separated)
• --exclude <patterns>: Exclude specific files or directories (comma-separated glob patterns)
• --include <patterns>: Include only specific files or directories (comma-separated glob patterns)
• --respect-gitignore: Respect .gitignore files when scanning directories (does not apply to explicitly provided paths)
• --force-exclude: Enforce exclude patterns even for explicitly specified files (useful for pre-commit hooks)
• -v, --verbose: Show detailed output
• --profile: Show profiling information
• --statistics: Show rule violation statistics summary
• -q, --quiet: Quiet mode
• -o, --output <format>: Output format: text (default) or json
• --stdin: Read from stdin instead of files

fmt [PATHS...]

Format Markdown files and output the result. Always exits with code 0 on successful formatting, making it ideal for editor integration.

Arguments:

• [PATHS...]: Files or directories to format. If provided, these paths take precedence over include patterns

Options:

All the same options as check are available (except --fix which is always enabled), including:

• --stdin: Format content from stdin and output to stdout
• -d, --disable <rules>: Disable specific rules during formatting
• -e, --enable <rules>: Format using only specific rules
• --exclude/--include: Control which files to format
• -q, --quiet: Suppress diagnostic output

Examples:

# Format all Markdown files in current directory
rumdl fmt

# Format specific file
rumdl fmt README.md

# Format from stdin (using dash syntax)
cat README.md | rumdl fmt - > formatted.md
# Alternative: cat README.md | rumdl fmt --stdin > formatted.md

init [OPTIONS]

Create a default configuration file in the current directory

Options:

• --pyproject: Generate configuration for pyproject.toml instead of .rumdl.toml

import <FILE> [OPTIONS]

Import and convert markdownlint configuration files to rumdl format

Arguments:

• <FILE>: Path to markdownlint config file (JSON/YAML)

Options:

• -o, --output <path>: Output file path (default: .rumdl.toml)
• --format <format>: Output format: toml or json (default: toml)
• --dry-run: Show converted config without writing to file

rule [<rule>]

Show information about a rule or list all rules

Arguments:

• [rule]: Rule name or ID (optional). If provided, shows details for that rule. If omitted, lists all available rules

config [OPTIONS] [COMMAND]

Show configuration or query a specific key

Options:

• --defaults: Show only the default configuration values
• --output <format>: Output format (e.g. toml, json)

Subcommands:

• get <key>: Query a specific config key (e.g. global.exclude or MD013.line_length)
• file: Show the absolute path of the configuration file that was loaded

server [OPTIONS]

Start the Language Server Protocol server for editor integration

Options:

• --port <PORT>: TCP port to listen on (for debugging)
• --stdio: Use stdio for communication (default)
• -v, --verbose: Enable verbose logging

vscode [OPTIONS]

Install the rumdl VS Code extension

Options:

• --force: Force reinstall even if already installed
• --status: Show installation status without installing

version

Show version information

Global Options

These options are available for all commands:

• --color <mode>: Control colored output: auto (default), always, never
• --config <file>: Path to configuration file
• --no-config: Ignore all configuration files and use built-in defaults

Exit Codes

• 0: Success
• 1: Violations found (or remain after --fix)
• 2: Tool error

Note: rumdl fmt exits 0 on successful formatting (even if unfixable violations remain), making it compatible with editor integrations. rumdl check --fix exits 1 if violations remain, useful for pre-commit hooks.

Usage Examples

# Lint all Markdown files in the current directory
rumdl check .

# Format files (exits 0 on success, even if unfixable violations remain)
rumdl fmt .

# Auto-fix and report unfixable violations (exits 1 if violations remain)
rumdl check --fix .

# Preview what would be fixed without modifying files
rumdl check --diff .

# Create a default configuration file
rumdl init

# Create or update a pyproject.toml file with rumdl configuration
rumdl init --pyproject

# Import a markdownlint config file
rumdl import .markdownlint.json

# Convert markdownlint config to JSON format
rumdl import --format json .markdownlint.yaml --output rumdl-config.json

# Preview conversion without writing file
rumdl import --dry-run .markdownlint.json

# Show information about a specific rule
rumdl rule MD013

# List all available rules
rumdl rule

# Query a specific config key
rumdl config get global.exclude

# Show the path of the loaded configuration file
rumdl config file

# Show configuration as JSON instead of the default format
rumdl config --output json

# Lint content from stdin
echo "# My Heading" | rumdl check --stdin

# Get JSON output for integration with other tools
rumdl check --output json README.md

# Show statistics summary of rule violations
rumdl check --statistics .

# Disable colors in output
rumdl check --color never README.md

# Use built-in defaults, ignoring all config files
rumdl check --no-config README.md

# Show version information
rumdl version

Configuration

rumdl can be configured in several ways:

1. Using a .rumdl.toml file in your project directory or parent directories
2. Using the [tool.rumdl] section in your project's pyproject.toml file (for Python projects)
3. Using command-line arguments
4. Automatic markdownlint compatibility: rumdl automatically discovers and loads existing markdownlint config files (.markdownlint.json, .markdownlint.yaml, etc.)

Configuration Discovery

rumdl automatically searches for configuration files by traversing up the directory tree from the current working directory, similar to tools like git , ruff , and eslint . This means you can run rumdl from any subdirectory of your project and it will find the configuration file at the project root.

The search follows these rules:

• Searches upward for .rumdl.toml, rumdl.toml, or pyproject.toml (with [tool.rumdl] section)
• Stops at the first configuration file found
• Stops searching when it encounters a .git directory (project boundary)
• Maximum traversal depth of 100 directories
• Falls back to user configuration if no project configuration is found (see Global Configuration below)

To disable all configuration discovery and use only built-in defaults, use the --isolated flag:

# Use discovered configuration (default behavior)
rumdl check .

# Ignore all configuration files
rumdl check --isolated .

Editor Support (JSON Schema)

rumdl provides a JSON Schema for .rumdl.toml configuration files, enabling autocomplete, validation, and inline documentation in supported editors like VS Code, IntelliJ IDEA, and others.

The schema is available at https://raw.githubusercontent.com/rvben/rumdl/main/rumdl.schema.json.

VS Code Setup:

1. Install the "Even Better TOML" extension
2. The schema will be automatically associated with .rumdl.toml and rumdl.toml files once submitted to SchemaStore

Manual Schema Association:

Add this to your .rumdl.toml file (in a comment, as TOML doesn't support $schema):

# yaml-language-server: $schema=https://raw.githubusercontent.com/rvben/rumdl/main/rumdl.schema.json

This enables IntelliSense, validation, and hover documentation for all configuration options.

Global Configuration

When no project configuration is found, rumdl will check for a user-level configuration file in your platform's standard config directory:

Location:

• Linux/macOS: ~/.config/rumdl/ (respects XDG_CONFIG_HOME if set)
• Windows: %APPDATA%\rumdl\

Files checked (in order):

1. .rumdl.toml
2. rumdl.toml
3. pyproject.toml (must contain [tool.rumdl] section)

This allows you to set personal preferences that apply to all projects without local configuration.

Example: Create ~/.config/rumdl/rumdl.toml:

[global]
line-length = 100
disable = ["MD013", "MD041"]

[MD007]
indent = 2

Note: User configuration is only used when no project configuration exists. Project configurations always take precedence.

Markdownlint Migration

rumdl provides seamless compatibility with existing markdownlint configurations:

** Automatic Discovery**: rumdl automatically detects and loads markdownlint config files:

• .markdownlint.json / .markdownlint.jsonc
• .markdownlint.yaml / .markdownlint.yml
• markdownlint.json / markdownlint.yaml

** Explicit Import**: Convert markdownlint configs to rumdl format:

# Convert to .rumdl.toml
rumdl import .markdownlint.json

# Convert to JSON format
rumdl import --format json .markdownlint.yaml --output config.json

# Preview conversion
rumdl import --dry-run .markdownlint.json

For comprehensive documentation on global settings (file selection, rule enablement, etc.), see our Global Settings Reference.

Inline Configuration

rumdl supports inline HTML comments to disable or configure rules for specific sections of your Markdown files. This is useful for making exceptions without changing global configuration:

<!-- rumdl-disable MD013 -->
This line can be as long as needed without triggering the line length rule.
<!-- rumdl-enable MD013 -->

Note: markdownlint-disable/markdownlint-enable comments are also supported for compatibility with existing markdownlint configurations.

For complete documentation on inline configuration options, see our Inline Configuration Reference.

Configuration File Example

Here's an example .rumdl.toml configuration file:

# Global settings
line-length = 100
exclude = ["node_modules", "build", "dist"]
respect-gitignore = true

# Disable specific rules
disabled-rules = ["MD013", "MD033"]

# Disable specific rules for specific files
[per-file-ignores]
"README.md" = ["MD033"]  # Allow HTML in README
"SUMMARY.md" = ["MD025"]  # Allow multiple H1 in table of contents
"docs/api/**/*.md" = ["MD013", "MD041"]  # Relax rules for generated docs

# Configure individual rules
[MD007]
indent = 2

[MD013]
line-length = 100
code-blocks = false
tables = false
reflow = true  # Enable automatic line wrapping (required for --fix)

[MD025]
level = 1
front-matter-title = "title"

[MD044]
names = ["rumdl", "Markdown", "GitHub"]

[MD048]
code-fence-style = "backtick"

Initializing Configuration

To create a configuration file, use the init command:

# Create a .rumdl.toml file (for any project)
rumdl init

# Create or update a pyproject.toml file with rumdl configuration (for Python projects)
rumdl init --pyproject

Configuration in pyproject.toml

For Python projects, you can include rumdl configuration in your pyproject.toml file, keeping all project configuration in one place. Example:

[tool.rumdl]
# Global options at root level
line-length = 100
disable = ["MD033"]
include = ["docs/*.md", "README.md"]
exclude = [".git", "node_modules"]
ignore-gitignore = false

# Rule-specific configuration
[tool.rumdl.MD013]
code_blocks = false
tables = false

[tool.rumdl.MD044]
names = ["rumdl", "Markdown", "GitHub"]

Both kebab-case (line-length, ignore-gitignore) and snake_case (line_length, ignore_gitignore) formats are supported for compatibility with different Python tooling conventions.

Configuration Output

Effective Configuration (rumdl config)

The rumdl config command prints the full effective configuration (defaults + all overrides), showing every key and its value, annotated with the source of each value. The output is colorized and the [from ...] annotation is globally aligned for easy scanning.

Example output

[global]
  enable             = []                             [from default]
  disable            = ["MD033"]                      [from .rumdl.toml]
  include            = ["README.md"]                  [from .rumdl.toml]
  respect_gitignore  = true                           [from .rumdl.toml]

[MD013]
  line_length        = 200                            [from .rumdl.toml]
  code_blocks        = true                           [from .rumdl.toml]
  ...

• ** Keys** are cyan, values are yellow, and the [from ...] annotation is colored by source:
  • Green: CLI
  • Blue: .rumdl.toml
  • Magenta: pyproject.toml
  • Yellow: default
• The [from ...] column is aligned across all sections.

Defaults Only (rumdl config --defaults)

The --defaults flag prints only the default configuration as TOML, suitable for copy-paste or reference:

[global]
enable = []
disable = []
exclude = []
include = []
respect_gitignore = true
force_exclude = false  # Set to true to exclude files even when explicitly specified

[MD013]
line_length = 80
code_blocks = true
...

Output Style

rumdl produces clean, colorized output similar to modern linting tools:

README.md:12:1: [MD022] Headings should be surrounded by blank lines [*]
README.md:24:5: [MD037] Spaces inside emphasis markers: "* incorrect *" [*]
README.md:31:76: [MD013] Line length exceeds 80 characters
README.md:42:3: [MD010] Hard tabs found, use spaces instead [*]

When running with --fix, rumdl shows which issues were fixed:

README.md:12:1: [MD022] Headings should be surrounded by blank lines [fixed]
README.md:24:5: [MD037] Spaces inside emphasis markers: "* incorrect *" [fixed]
README.md:42:3: [MD010] Hard tabs found, use spaces instead [fixed]

Fixed 3 issues in 1 file

For a more detailed view, use the --verbose option:

✓ No issues found in CONTRIBUTING.md
README.md:12:1: [MD022] Headings should be surrounded by blank lines [*]
README.md:24:5: [MD037] Spaces inside emphasis markers: "* incorrect *" [*]
README.md:42:3: [MD010] Hard tabs found, use spaces instead [*]

Found 3 issues in 1 file (2 files checked)
Run `rumdl fmt` to automatically fix issues

Output Format

Text Output (Default)

rumdl uses a consistent output format for all issues:

{file}:{line}:{column}: [{rule_id}] {message} [{fix_indicator}]

The output is colorized by default:

• Filenames appear in blue and underlined
• Line and column numbers appear in cyan
• Rule IDs appear in yellow
• Error messages appear in white
• Fixable issues are marked with [*] in green
• Fixed issues are marked with [fixed] in green

JSON Output

For integration with other tools and automation, use --output json:

rumdl check --output json README.md

This produces structured JSON output:

{
  "summary": {
    "total_files": 1,
    "files_with_issues": 1,
    "total_issues": 2,
    "fixable_issues": 1
  },
  "files": [
    {
      "path": "README.md",
      "issues": [
        {
          "line": 12,
          "column": 1,
          "rule": "MD022",
          "message": "Headings should be surrounded by blank lines",
          "fixable": true,
          "severity": "error"
        }
      ]
    }
  ]
}

Development

Prerequisites

• Rust 1.91 or higher
• Make (for development commands)

Building

make build

Testing

make test

JSON Schema Generation

If you modify the configuration structures in src/config.rs, regenerate the JSON schema:

# Generate/update the schema
make schema
# Or: rumdl schema generate

# Check if schema is up-to-date (useful in CI)
make check-schema
# Or: rumdl schema check

# Print schema to stdout
rumdl schema print

The schema is automatically generated from the Rust types using schemars and should be kept in sync with the configuration structures.

License

rumdl is licensed under the MIT License. See the LICENSE file for details.