mkdlint

A fast Markdown linter written in Rust, inspired by markdownlint.

Features

64 lint rules (MD001-MD060 + KMD001-KMD011) enforcing Markdown best practices
Automatic fixing for 58 rules (90.6% coverage) with --fix flag
Helpful suggestions for all rules with actionable guidance
VS Code extension with bundled LSP server
Language Server Protocol (LSP) for real-time linting in any editor
GitHub Action with SARIF Code Scanning, job summaries, and incremental linting
Rich error display with source context and colored underlines
Multiple output formats -- text (default), JSON, or SARIF
Configuration via JSON, YAML, or TOML files with auto-discovery
High performance -- zero-copy lines, static strings, conditional parsing
Library + CLI -- use as a Rust crate or standalone command-line tool

Installation

VS Code Extension

Install from the VS Code Marketplace or search "mkdlint" in the Extensions panel. The extension bundles the LSP server -- no separate install needed.

CLI Tool

# From crates.io
cargo install mkdlint

# From source
cargo install --path .

# With Homebrew (macOS/Linux)
brew install 192d-Wing/tap/mkdlint

# With Docker
docker run --rm -v $(pwd):/work ghcr.io/192d-wing/mkdlint .

# With pre-commit
# See pre-commit section below

Language Server (LSP)

# Install with LSP feature
cargo install mkdlint --features lsp

# The binary will be available as: mkdlint-lsp

GitHub Action (Quick Start)

Add to your workflow:

- uses: 192d-Wing/mkdlint/.github/actions/mkdlint@main
  with:
    files: '.'

See GitHub Action documentation for full details.

As a Library Dependency

[dependencies]
mkdlint = "0.11"

# With async support
mkdlint = { version = "0.11", features = ["async"] }

# With LSP support
mkdlint = { version = "0.11", features = ["lsp"] }

Auto-Fix Showcase

mkdlint can automatically fix 58 out of 64 rules (90.6%)! Here are some examples:

Before Auto-Fix

#Missing space after hash

![](image.png)

# Title
# Another Title

>Blockquote with  trailing spaces
>
>And blank lines inside

[link](http://example.com)
http://example.com

$ npm install
$ echo "commands with dollar signs"

After `mkdlint --fix`

# Missing space after hash

![image](image.png)

# Title

## Another Title

> Blockquote with trailing spaces
> And blank lines inside

[link](http://example.com)
<http://example.com>

npm install
echo "commands with dollar signs"

What Gets Fixed Automatically

Headings: spacing, levels, ATX style consistency
Links & Images: alt text, bare URLs, unused references
Lists: indentation, marker consistency, spacing
Code: fence styles, dollar sign prefixes, language tags
Whitespace: trailing spaces, blank lines, tabs
Tables: pipe consistency, surrounding blank lines
And much more!

CLI Usage

Basic Commands

# Lint files
mkdlint README.md docs/*.md

# Lint with auto-fix
mkdlint --fix README.md

# Lint a directory recursively
mkdlint docs/

# Lint from stdin
cat README.md | mkdlint --stdin

# List all available rules with descriptions
mkdlint --list-rules

Configuration Management

# Initialize a new config file with defaults
mkdlint init

# Initialize with custom path and format
mkdlint init --output .mkdlint.yaml --format yaml

# Use a specific config file
mkdlint --config .markdownlint.json README.md

# Enable/disable specific rules on the fly
mkdlint --enable MD001 --disable MD013 README.md

# Combine multiple rule overrides
mkdlint --config base.json --enable MD001 --disable MD033 docs/

Kramdown Preset

For authors writing RFCs and technical documents using Kramdown syntax:

# Enable Kramdown mode via CLI flag
mkdlint --preset kramdown doc.md

# Or set it in your config file

{
  "preset": "kramdown"
}

The kramdown preset:

Disables MD033 (inline HTML) — Kramdown IAL syntax {: #id .class key="val"} looks like inline HTML
Disables MD041 (first heading required) — RFC preambles often start with metadata, not headings
Enables 11 Kramdown-specific rules (off by default):

Rule	Name	Description
KMD001	`definition-list-term-has-definition`	DL terms must be followed by `: definition`
KMD002	`footnote-refs-defined`	`[^label]` refs must have matching `[^label]:` defs
KMD003	`footnote-defs-used`	`[^label]:` defs must be referenced in the document
KMD004	`abbreviation-defs-used`	`*[ABBR]: ...` defs must appear as text
KMD005	`no-duplicate-heading-ids`	Heading IDs (explicit or auto-slug) must be unique
KMD006	`valid-ial-syntax`	`{: ...}` block-level IAL lines must be well-formed
KMD007	`math-block-delimiters`	Block `$$` math fences must be matched
KMD008	`block-extension-syntax`	`{::name}...{:/name}` extensions must be opened and closed
KMD009	`ald-defs-used`	`{:ref-name: attrs}` ALDs must be referenced
KMD010	`inline-ial-syntax`	Inline `text{: .class}` IAL must be well-formed
KMD011	`inline-math-balanced`	Inline $...$ math spans must have balanced `$` delimiters

You can enable individual KMD rules without the full preset:

{
  "KMD002": true,
  "KMD007": true,
  "KMD010": true
}

GitHub Preset

For documentation hosted on GitHub, using GitHub Flavored Markdown (GFM):

mkdlint --preset github doc.md

{
  "preset": "github"
}

The github preset:

Sets MD003 heading style to consistent — GFM renders both ATX and setext, but they should not be mixed
Disables MD013 (line length) — long lines are common in GFM tables and URLs
Disables MD034 (bare URLs) — GitHub auto-links bare URLs in some contexts

Output Control

# Output in JSON format (machine-readable)
mkdlint --output-format json README.md

# Output in SARIF format (for CI/CD integration)
mkdlint --output-format sarif README.md

# Quiet mode - only show filenames with errors
mkdlint --quiet docs/

# Verbose mode - show detailed error statistics
mkdlint --verbose docs/

# Disable colored output (for CI environments)
mkdlint --no-color README.md

Advanced Usage

# Ignore specific files/patterns
mkdlint --ignore "**/node_modules/**" --ignore "**/.git/**" .

# Combine multiple options
mkdlint --config .mkdlint.json \
       --ignore "build/**" \
       --ignore "dist/**" \
       --fix \
       --verbose \
       .

# Fix with specific rules disabled
mkdlint --fix --disable MD013 --disable MD033 docs/

# Stdin with fix output to stdout
cat README.md | mkdlint --stdin --fix > README_fixed.md

Example Output

mkdlint provides rich error display with source context:

README.md: 42: MD009/no-trailing-spaces Trailing spaces [Expected: 0; Actual: 3]
  42 |
  42 |  This line has trailing spaces
     |                               ^^^

README.md: 58: MD034/no-bare-urls Bare URL used
  58 |
  58 |  Visit https://example.com for more info.
     |        ^^^^^^^^^^^^^^^^^^^

Commands

Command	Description
`mkdlint [FILES...]`	Lint markdown files (default command)
`mkdlint init`	Create a new configuration file with defaults

Options

Flag	Description
`-f`, `--fix`	Automatically fix violations where possible
`-c`, `--config <PATH>`	Path to configuration file (.json, .yaml, or .toml)
`-o`, `--output-format <FORMAT>`	Output format: `text` (default), `json`, or `sarif`
`--ignore <PATTERN>`	Glob pattern to ignore (can be repeated)
`--stdin`	Read input from stdin instead of files
`--list-rules`	List all available linting rules with descriptions
`--enable <RULE>`	Enable specific rule (can be repeated)
`--disable <RULE>`	Disable specific rule (can be repeated)
`-v`, `--verbose`	Show detailed output with error statistics
`-q`, `--quiet`	Quiet mode - only show filenames with errors
`--no-color`	Disable colored output
`--no-inline-config`	Disable inline configuration comments

VS Code Extension

Install from the Marketplace or use the bundled extension in editors/vscode/.

Features:

Real-time diagnostics as you type
Quick-fix code actions (Ctrl+.)
"Fix All Issues" command
Status bar with error/warning counts
Respects .markdownlint.json config

Settings:

Setting	Description	Default
`mkdlint.enable`	Enable/disable linting	`true`
`mkdlint.path`	Override mkdlint-lsp binary path	`null`
`mkdlint.trace.server`	LSP trace level for debugging	`off`

Language Server Protocol (LSP)

mkdlint includes a full-featured Language Server for real-time linting in your editor.

Neovim Setup

require('lspconfig').mkdlint.setup{
  cmd = { '/path/to/mkdlint-lsp' },
  filetypes = { 'markdown' },
  root_dir = require('lspconfig.util').root_pattern('.markdownlint.json', '.git'),
}

Other Editors

Any editor with LSP support can use mkdlint-lsp. The server uses stdio for communication and supports:

textDocument/didOpen, didChange, didSave, didClose
textDocument/codeAction (for individual auto-fixes)
workspace/executeCommand (for "Fix All" command)
Full document synchronization

CI/CD Integration

GitHub Action

name: Lint Markdown
on: [push, pull_request]

jobs:
  lint:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      security-events: write

    steps:
      - uses: actions/checkout@v4

      - uses: 192d-Wing/mkdlint/.github/actions/mkdlint@main
        with:
          files: '.'

Features:

Pre-built binaries for Linux, macOS, Windows (x86_64, aarch64)
Automatic binary caching (10-100x faster subsequent runs)
SARIF output with automatic Code Scanning upload
Rich job summary with error counts and top violated rules
Incremental linting -- only lint changed files in PRs (changed-only: true)
Performance timing in outputs (duration-ms)
Auto-fix support with commit integration

See full documentation for all options.

pre-commit

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

repos:
  - repo: https://github.com/192d-Wing/mkdlint
    rev: main
    hooks:
      - id: mkdlint

Docker

# Lint current directory
docker run --rm -v $(pwd):/work ghcr.io/192d-wing/mkdlint .

# Lint with auto-fix
docker run --rm -v $(pwd):/work ghcr.io/192d-wing/mkdlint --fix .

# Lint specific files
docker run --rm -v $(pwd):/work ghcr.io/192d-wing/mkdlint README.md docs/

Library Usage

use mkdlint::{lint_sync, apply_fixes, LintOptions};

let options = LintOptions {
    files: vec!["README.md".to_string()],
    ..Default::default()
};

let results = lint_sync(&options).unwrap();
for (file, errors) in results.iter() {
    for error in errors {
        println!("{}: {}", file, error);
    }
}

Auto-fixing

use mkdlint::{lint_sync, apply_fixes, LintOptions};
use std::collections::HashMap;

let content = "# Title\n\nSome text   \n";
let mut strings = HashMap::new();
strings.insert("test.md".to_string(), content.to_string());

let options = LintOptions { strings, ..Default::default() };
let results = lint_sync(&options).unwrap();

if let Some(errors) = results.get("test.md") {
    let fixed = apply_fixes(content, errors);
    println!("{}", fixed); // trailing whitespace removed
}

Configuration

Create a .markdownlint.json (or .yaml / .toml) file:

{
  "default": true,
  "MD013": { "line_length": 120 },
  "MD033": false
}

Rules can be enabled/disabled by name ("MD013") or alias ("line-length"). Pass a boolean to enable/disable, or an object to configure options.

Rules

Rule	Alias	Description	Fixable
MD001	heading-increment	Heading levels should increment by one	Yes
MD003	heading-style	Heading style	Yes
MD004	ul-style	Unordered list style	Yes
MD005	list-indent	Inconsistent indentation for list items	Yes
MD007	ul-indent	Unordered list indentation	Yes
MD009	no-trailing-spaces	Trailing spaces	Yes
MD010	no-hard-tabs	Hard tabs	Yes
MD011	no-reversed-links	Reversed link syntax	Yes
MD012	no-multiple-blanks	Multiple consecutive blank lines	Yes
MD013	line-length	Line length
MD014	commands-show-output	Dollar signs used before commands	Yes
MD018	no-missing-space-atx	No space after hash on atx heading	Yes
MD019	no-multiple-space-atx	Multiple spaces after hash on atx heading	Yes
MD020	no-missing-space-closed-atx	No space inside hashes on closed atx heading	Yes
MD021	no-multiple-space-closed-atx	Multiple spaces inside hashes on closed atx heading	Yes
MD022	blanks-around-headings	Headings should be surrounded by blank lines	Yes
MD023	heading-start-left	Headings must start at the beginning of the line	Yes
MD024	no-duplicate-heading	No duplicate heading content	Yes
MD025	single-title	Single title / single h1	Yes
MD026	no-trailing-punctuation	Trailing punctuation in heading	Yes
MD027	no-multiple-space-blockquote	Multiple spaces after blockquote symbol	Yes
MD028	no-blanks-blockquote	Blank line inside blockquote	Yes
MD029	ol-prefix	Ordered list item prefix	Yes
MD030	list-marker-space	Spaces after list markers	Yes
MD031	blanks-around-fences	Fenced code blocks should be surrounded by blank lines	Yes
MD032	blanks-around-lists	Lists should be surrounded by blank lines	Yes
MD033	no-inline-html	Inline HTML
MD034	no-bare-urls	Bare URL used	Yes
MD035	hr-style	Horizontal rule style	Yes
MD036	no-emphasis-as-heading	Emphasis used instead of a heading	Yes
MD037	no-space-in-emphasis	Spaces inside emphasis markers	Yes
MD038	no-space-in-code	Spaces inside code span elements	Yes
MD039	no-space-in-links	Spaces inside link text	Yes
MD040	fenced-code-language	Fenced code blocks should have a language specified	Yes
MD041	first-line-heading	First line in a file should be a top-level heading	Yes
MD042	no-empty-links	No empty links	Yes
MD043	required-headings	Required heading structure
MD044	proper-names	Proper names should have correct capitalization	Yes
MD045	no-alt-text	Images should have alternate text	Yes
MD046	code-block-style	Code block style	Yes
MD047	single-trailing-newline	Files should end with a single trailing newline	Yes
MD048	code-fence-style	Code fence style	Yes
MD049	emphasis-style	Emphasis style	Yes
MD050	strong-style	Strong style	Yes
MD051	link-fragments	Link fragments should be valid
MD052	reference-links-images	Reference links and images should use a defined label	Yes
MD053	link-image-reference-definitions	Link and image reference definitions should be needed	Yes
MD054	link-image-style	Link and image style	Yes
MD055	table-pipe-style	Table pipe style	Yes
MD056	table-column-count	Table column count
MD058	blanks-around-tables	Tables should be surrounded by blank lines	Yes
MD059	emphasis-marker-style-math	Emphasis marker style in math	Yes
MD060	dollar-in-code-fence	Dollar signs in fenced code blocks	Yes

Kramdown Extension Rules (off by default)

Rule	Alias	Description	Fixable
KMD001	definition-list-term-has-definition	Definition list terms must be followed by a definition
KMD002	footnote-refs-defined	Footnote references must have matching definitions
KMD003	footnote-defs-used	Footnote definitions must be referenced in the document
KMD004	abbreviation-defs-used	Abbreviation definitions should be used in document text
KMD005	no-duplicate-heading-ids	Heading IDs must be unique within the document	Yes
KMD006	valid-ial-syntax	IAL (Inline Attribute List) syntax must be well-formed	Yes
KMD007	math-block-delimiters	Math block `$$` delimiters must be matched	Yes
KMD008	block-extension-syntax	Block extensions must be properly opened and closed	Yes
KMD009	ald-defs-used	Attribute List Definitions must be referenced in the document	Yes
KMD010	inline-ial-syntax	Inline IAL syntax must be well-formed	Yes
KMD011	inline-math-balanced	Inline math spans must have balanced '$' delimiters

58 of 64 rules have auto-fix support (90.6% coverage).

License

Apache-2.0

mkdlint 0.11.3

mkdlint

Features

Installation

VS Code Extension

CLI Tool

Language Server (LSP)

GitHub Action (Quick Start)

As a Library Dependency

Auto-Fix Showcase

Before Auto-Fix

After mkdlint --fix

What Gets Fixed Automatically

CLI Usage

Basic Commands

Configuration Management

Kramdown Preset

GitHub Preset

Output Control

Advanced Usage

Example Output

Commands

Options

VS Code Extension

Language Server Protocol (LSP)

Neovim Setup

Other Editors

CI/CD Integration

GitHub Action

pre-commit

Docker

Library Usage

Auto-fixing

Configuration

Rules

Kramdown Extension Rules (off by default)

License

After `mkdlint --fix`