mdr 0.6.1

A lightweight Markdown viewer with live reload and multiple rendering backends
mdr-0.6.1 is not a library.

Why mdr?

Built for the LLM era. AI tools generate Markdown constantly — code documentation, technical specs, analysis reports — packed with diagrams, tables, and structured content. You need a fast way to read them.

Most developers end up previewing Markdown in VS Code, pasting into a browser, or squinting at raw text in the terminal. mdr renders Mermaid diagrams itself, and opens the file you give it without a project, a server or an extension.

  • One command — mdr file.md and you're reading, not editing
  • Native Rust binary — no Electron, no Node.js, no npm
  • Mermaid diagrams — flowcharts, sequence diagrams, pie charts rendered as SVG natively (no headless browser)
  • Three backends — a native window (gui), the system webview (web), or a terminal UI (tui) over SSH
  • Live reload — edit your file or let your AI tool regenerate it, see changes instantly
  • In-document search — Ctrl+F / / to find text across all backends
  • Fully keyboard-driven — every backend quits, scrolls, searches and navigates from the keyboard

Backends

mdr offers multiple rendering backends, selectable at runtime:

Backend Stack Strengths
gui Pure Rust GPU rendering (egui) Native window, no JavaScript engine, cross-platform
web OS native WebView (WebKit/WebView2) GitHub-quality HTML/CSS rendering, full CSS support
tui Terminal UI (ratatui + crossterm) Works over SSH, no GUI needed, keyboard-driven

--backend and the backend key of the config file pick one. The default is auto, which chooses among the backends this binary was built with: tui over SSH or with no display, and otherwise the first of gui and web that is compiled in.

Install

From crates.io

cargo install mdr
# or, to download the release binary instead of compiling
cargo binstall mdr

Note: cargo install compiles the three backends; on Linux that needs the system dependencies below. cargo binstall downloads the release binary instead.

From source

git clone https://github.com/CleverCloud/mdr.git
cd mdr
cargo install --path .

Build with specific backends only

# gui only (smaller binary, no WebView dependency)
cargo install --path . --no-default-features --features egui-backend

# web only
cargo install --path . --no-default-features --features webview-backend

Homebrew (macOS/Linux)

brew install CleverCloud/misc/mdr

Snap (Linux)

sudo snap install --edge mdr-markdown-renderer

Note: The snap command is mdr-markdown-renderer, not mdr. You can create an alias: sudo snap alias mdr-markdown-renderer mdr

Scoop (Windows)

scoop bucket add clevercloud https://github.com/CleverCloud/scoop-bucket
scoop install mdr

Chocolatey (Windows)

choco install mdr

WinGet (Windows)

winget install CleverCloud.mdr

Nix

nix run github:CleverCloud/mdr

Pre-built binaries

Download from the Releases page for macOS, Linux, and Windows.

Usage

# Open with the backend mdr picks for this session
mdr README.md

# Open with the web backend
mdr --backend web README.md

# Open in terminal (TUI)
mdr --backend tui README.md

# Never touch the network (remote images are left unresolved)
mdr --offline README.md

# Render in the light colour scheme
mdr -t light README.md

# Show help
mdr --help

In web, clicking an http(s) link opens it in your system browser, and a link to another local .md file opens that file in mdr. gui and tui have no such routing.

gui keybindings

Key Action
q, Esc, Ctrl/Cmd+Q, Ctrl/Cmd+W Quit
Ctrl/Cmd+F Search in the document
Esc Close the search (quits when no search is open)
F10 Show or hide the table of contents
t Switch between the light and dark theme
j / ↓, k / ↑ Scroll down / up
Space / PgDn, PgUp Page down / up
g / Home, G / End Go to top / bottom

On macOS the shortcuts use ⌘, not ⌃.

web keybindings

Press ? in the web backend for this list.

Key Action
Ctrl/Cmd+Q Close the window
Ctrl/Cmd+F Search in the document
n / N Next / previous search match
Esc Close search, help or the expanded image
j / ↓, k / ↑ Scroll down / up
Space / PgDn, PgUp Page down / up
g / Home, G / End Go to top / bottom
Ctrl/Cmd + + / - / 0 Zoom in / out / reset
Ctrl/Cmd+B Show or hide the table of contents
t Switch between the light and dark theme
Ctrl/Cmd+P Print or export to PDF
? Show or hide the shortcut list

t flips the colour scheme of the current window, whether it came from prefers-color-scheme or from --theme. It is a bare key on purpose: Ctrl/Cmd+D is a split-pane shortcut in most terminals. Mermaid diagrams are the exception: one rendered to SVG carries its own colours from the start, and one drawn in the page is not recoloured once it is on screen.

TUI keybindings

Key Action
q / Esc / Ctrl+C Quit
j / ↓ Scroll down
k / ↑ Scroll up
Space / PgDn Page down
PgUp Page up
g / Home Go to top
G / End Go to bottom
Tab Switch focus between TOC and content
Enter Navigate to selected TOC heading
/ or Ctrl+F Open search
n Next search match
N Previous search match
t Switch between the light and dark theme

The terminal owns its own background, so t here switches the colours code blocks are highlighted in. Each block paints the theme's own background, so both themes stay legible whatever the terminal is set to.

Features

  • GFM — tables, task lists, strikethrough, footnotes, autolinks. gui draws tables itself
  • One parser for the structure — comrak produces the HTML web renders, the lines tui draws, and the headings every table of contents is built from. gui draws through egui_commonmark, which reads the Markdown again with its own parser, so its typography — and, for tables and raw HTML, its rendering — is its own
  • Raw HTML in a document — web hands it to a real engine. gui has none, so a short, explicit set of tags (headings, paragraphs, images) is rewritten as the Markdown that means the same thing, and anything else keeps its text and loses its tags. Only blocks at the top level of the document are converted; one nested in a quote or a list is left as written. Attributes with no Markdown equivalent, such as align="center", are dropped, <br> becomes a space, and a declared width is honoured for vector images. A heading written in HTML becomes a real heading, so it appears in the gui table of contents where web does not list it. tui shows HTML as the text it is
  • Syntax highlighting — code blocks with language detection (via syntect), in the terminal too. The palette follows the terminal background when it says what it is (COLORFGBG), and falls back to a dark one; --theme dark|light or theme "light" in the config file settles it when the terminal stays silent — Terminal.app and Alacritty do. The same setting picks the palette in gui and web.
  • Mermaid diagrams — flowcharts, sequence diagrams, pie charts, and more (via mermaid-rs-renderer)
  • Table of Contents — auto-generated sidebar from headings with click-to-navigate
  • Live reload — file watching with 300ms debounce, updates on save
  • Dark/Light theme — follows the OS by default; --theme dark|light (or theme in the config file) settles it. In gui and web it picks the whole palette; in tui the terminal owns its own colours, so it selects the syntax highlighting of code blocks and nothing more. t flips the scheme live in every backend
  • YAML front matter — recognised as metadata, so it is neither rendered nor listed in the TOC
  • Unique heading anchors — repeated headings get setup, setup-1, … as GitHub does

Images

In gui and web, images are inlined into the document before rendering, so nothing is fetched while you read. tui loads an image when it draws it, and has its own path for that: no cache, and none of the size ceiling described below.

  • Local images resolve relative to the Markdown file, and may live anywhere inside the enclosing project — the nearest ancestor directory holding a .git, .hg, .svn or .jj. That makes the usual docs/page.md → ![](../images/schema.png) layout work. The search for that marker stops at your home directory, so a document outside any project is restricted to its own directory. Anything outside the root that comes out of this is refused.
  • A document read from stdin has no directory of its own — cat README.md | mdr writes it to a temp file — so its relative image paths resolve from the directory mdr was run in. cd docs && cat page.md | mdr therefore resolves them against docs, whatever directory page.md itself lives in. Links to other local files are not redirected this way: in web they are still resolved next to the temp file, so a piped document cannot follow them.
  • Remote images (http/https, typically README badges) are downloaded once, cached for the lifetime of the process, and embedded as data: URIs. Responses larger than 16 MB are ignored.
  • mdr --offline file.md disables every network access; remote images are then left unresolved. The same can be set permanently with offline #true in the config file.

Configuration

mdr writes a commented config file with its defaults the first time it runs, so there is nothing to scaffold and no flag to know about. Where it lands follows the platform:

Order Path
1 ~/.config/mdr/config.kdl, if it already exists
2 $XDG_CONFIG_HOME/mdr/config.kdl, when that variable holds an absolute path
3 %APPDATA%\mdr\config.kdl, on Windows
4 ~/.config/mdr/config.kdl

The order is the same on every platform; only step 3 is Windows-only. HOME gives the home directory, except on Windows where %USERPROFILE% comes first, since Git Bash sets HOME to a POSIX path a native binary cannot resolve.

Step 1 is a deliberate departure from the XDG spec, which says the variable wins: every mdr before 0.6 read ~/.config/mdr/config.kdl and nothing else, so letting XDG_CONFIG_HOME take precedence would silently ignore the config of everyone who has both. A relative XDG_CONFIG_HOME is ignored with a warning, as the spec requires. -c, --config PATH points somewhere else; a path given there must exist, since a typo is a mistake rather than a request to create a file.

If no environment variable names a home directory, mdr says so and reads ./.config/mdr/config.kdl if it happens to exist — but does not create one there, rather than leaving a .config/ behind in whatever directory it was started from. A file that is already there is treated like any other config, old backend name included.

The file is KDL v2. Four keys are recognised, each mirroring the command line option of the same name:

mdr -s web writes the backend into the file for you, leaving comments and every other setting alone; it refuses a backend the binary was not built with.

The backends were called egui and webview before 0.6. A config file holding one of the old names is corrected in place the first time it is read — comments and every other setting kept — and the run says so once. A file mdr cannot write, because it is read-only or a symlink, is left alone with a warning and still read with the old name understood. On the command line there is no such mapping: --backend egui is not a backend any more, and the error lists the ones that are.

backend auto      // auto, gui, tui or web
verbose #true     // same as -v
offline #true     // same as --offline
theme "auto"      // auto, dark or light

Mermaid Support

Mermaid code fences are rendered as SVG diagrams:

```mermaid
graph TD
    A[Input] --> B[Process]
    B --> C[Output]
```

Supported diagram types: flowchart, sequence, pie, class, state, ER, gantt.

Note: Diamond/decision nodes ({text}) are not yet supported by the underlying renderer. Use square brackets as a workaround.

Architecture

src/
├── main.rs              # CLI (clap), backend dispatch
├── core/
│   ├── markdown.rs      # GFM parsing (comrak) + CSS
│   ├── mermaid.rs       # Mermaid → SVG rendering
│   ├── toc.rs           # Heading extraction for TOC
│   ├── slug.rs          # Heading anchors, shared by the renderer and the TOC
│   ├── sanitize.rs      # Strips scripts and event handlers from raw HTML
│   ├── paths.rs         # Which directory tree images may be read from
│   ├── net.rs           # Remote image fetching (respects --offline)
│   └── watcher.rs       # File watching (notify, 300ms debounce)
└── backend/
    ├── egui.rs          # `gui` backend (egui/eframe)
    ├── tui.rs           # ratatui/crossterm TUI backend
    └── webview.rs       # `web` backend (wry/tao)

Building

Requires Rust 1.95 or later (the floor comes from kdl; the MSRV is checked in CI).

# All backends (default)
cargo build --release

# Run tests
cargo test

# Run clippy exactly as CI does
cargo clippy --all-features --all-targets -- -D warnings

Linux dependencies

sudo apt-get install libgtk-3-dev libwebkit2gtk-4.1-dev libxdo-dev libgl1-mesa-dev

Releases

Pre-built binaries are available on the Releases page for:

  • macOS (Apple Silicon + Intel)
  • Linux (x86_64 + aarch64)
  • Windows (x86_64)

Each release publishes to crates.io, and updates the Homebrew tap, the Scoop bucket, the Chocolatey package and the Snap Store (edge channel) for whichever of those channels is enabled — each one is gated on its own variable and needs its own secret, so a release still succeeds when a channel is not configured. See PACKAGING.md for the setup.

Release notes are the matching section of CHANGELOG.md, so add it before pushing the tag.

To create a release, push a version tag:

git tag v0.4.0
git push origin v0.4.0

License

MIT

Contributing

Issues and PRs welcome at github.com/CleverCloud/mdr.