mdwright

A Markdown linter and round-trip formatter for any Markdown project. mdwright fmt is HTML-equivalent to its input: it refuses any rewrite that would change the rendered DOM.

Fast. On a 79-file corpus of math-heavy technical prose, mdwright fmt-check runs ≥ 50× faster than mdformat --check. Multipliers scale with file count and core count; see Performance for the measurement and host details.

Configurable, preserve by default. Source style choices — emphasis delimiters (_foo_ vs *foo*), list markers (- / * / +), thematic breaks, link-destination angle brackets — pass through untouched. Canonicalisation is opt-in one knob at a time in .mdwright.toml, or via fmt.profile = "mdformat" for mdformat-compatible spelling where verified rewrites preserve the parsed document.

Math-resilient. Math regions (\( … \), \[ … \], \begin{…} … \end{…}, $ … $) pass through verbatim, so the tool stays safe on technical writing too. The lint catalogue also covers control-sequence patterns that generic Markdown formatters routinely mangle.

Documentation

Full manual: https://jcreinhold.github.io/mdwright/

• Getting started
• Rules catalogue
• Configuration
• Math rendering
• Integration

Installation

# One-line install (Linux x86_64, macOS aarch64). No Rust toolchain required.
curl --proto '=https' --tlsv1.2 -LsSf \
  https://github.com/jcreinhold/mdwright/releases/latest/download/mdwright-installer.sh | sh

# Or from crates.io (any target with a Rust toolchain).
cargo install mdwright

# Or via cargo-binstall (Rust + binstall).
cargo binstall mdwright

Tarballs for each release are attached to the GitHub Releases page. See Installation for the full platform support matrix.

Quick start

# CI idiom: lint + format-check together, exit non-zero on any failure.
mdwright check --check . && mdwright fmt-check .

# Lint a tree (exits 0 even with diagnostics; add --check to fail).
mdwright check docs/

# Apply every safe autofix in place.
mdwright fix docs/

# Reformat (round-trip safe).
mdwright fmt docs/

# Read a single file from stdin.
cat note.md | mdwright check -

Subcommand	Writes	Exit non-zero when
mdwright check	nothing	--check is set and a non-advisory diagnostic fires
mdwright fix	files (safe fixes)	--check is set and a non-advisory diagnostic still remains
mdwright fmt	files (every input)	parse fails or the safety gate refuses the rewrite
mdwright fmt-check	nothing	any input would be reformatted

See Lint vs. format for when each fires.

A diagnostic looks like:

error[bare-url]: bare URL should be wrapped in angle brackets or rendered as a link
  --> README.md:3:5
   |
 3 | See https://example.com for the spec.
   |     ^^^^^^^^^^^^^^^^^^^
   = help: CommonMark autolinks need angle brackets (`<https://example.com>`) to render as a link.
   = fix (safe): <https://example.com>
   = note: see `mdwright explain bare-url`

Every rule has a long-form explanation: mdwright explain <rule> prints the rationale and a link to the rendered rule page.

Pass files, directories, or both; directories are walked recursively with .gitignore honoured. mdwright lsp runs a built-in language server over stdio; recipes for Helix, Zed, VS Code, and Neovim are at Editor integration.

Configure

mdwright walks up from $PWD to find a .mdwright.toml, mdwright.toml, or pyproject.toml [tool.mdwright]. Out of the box, no config file is needed: defaults preserve your source. A minimal .mdwright.toml looks like:

[lint]
# `default` enables the curated baseline; `ignore` removes rules.
preset = "default"
ignore = ["bare-url"]

[fmt]
list-marker = "dash"          # canonicalise list markers to `-`

See Configuration for the full schema.

Wire into an existing project

pre-commit:

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/jcreinhold/mdwright
    rev: v0.1.1
    hooks:
      - id: mdwright-check-system
      - id: mdwright-fmt-check-system

GitHub Actions:

- uses: jcreinhold/mdwright@v0.1.1
  with:
    args: check --check .

Full recipes (including the language: rust variants that don't need mdwright on $PATH): see Pre-commit and GitHub Actions.

Exit codes

Code	Meaning
0	Success. With --check: no non-advisory diagnostics.
1	--check and at least one non-advisory diagnostic was reported.
2	I/O, argument, or other operational error (details on stderr).

Safety

mdwright is built to run on untrusted Markdown. The only user-tunable bound is --max-input-bytes (default 10 MB); three further bounds are fixed at compile time and degrade gracefully. Paragraphs that overrun the token cap or 100 ms wrap budget are emitted without re-wrapping rather than failing the run. Five coverage-guided fuzz targets under fuzz/ cover parse/format HTML equivalence, idempotence, lint determinism, and verbatim identity; reproducers for fixed bugs live under crates/mdwright/tests/regressions/. Panics on any input are security bugs; see SECURITY.md for disclosure.

Compared to mdformat

mdwright is not a drop-in mdformat clone. The release gate includes cargo xtask mdformat-parity, which compares both formatters on isolated corpus copies and records every byte-output difference as fixed, configured, intentional, or upstream-owned in docs/architecture/mdformat-parity.md. [fmt] profile = "mdformat" opts into mdformat-compatible spelling where verified rewrites preserve the parsed document.

Platform support

CI runs Linux × macOS × Windows against stable Rust and the 1.91 MSRV on every push and pull request. See .github/workflows/ci.yml for the matrix.

For contributors

Building from a clone, the Rust library crates, and writing custom lint rules are documented on the doc site:

• Building
• Public API surface
• Extending → Lint rules
• Architecture
• CONTRIBUTING.md for the MSRV-bump policy and PR conventions.