MD Viewer

A small, fast desktop reader for Markdown files. Double-click a .md file in Windows Explorer and it opens, rendered — no browser, no editor chrome, no white flash before the text appears.

Two documents open as tabs in the title bar — the window has no caption, so the toolbar is it — with the reading surface running edge to edge.

Install

Download the latest release

	File	What it does
Installer (recommended)	MD.Viewer_<version>_x64-setup.exe	Installs per user, registers the .md handler (and offers .txt), and pulls in the WebView2 runtime if the machine lacks it.
Portable	MD.Viewer_<version>_x64-portable.exe	The same build as a single file. Run it from anywhere; nothing to install. Use Set as default in Settings, or --register-default, when you want it to claim the file types.

Both are built from the tagged source, and each release ships a SHA256SUMS-<version>.txt. The binaries are not code-signed yet, so Windows SmartScreen may warn on the first run.

For scripted or headless setups, mdviewer.exe --register-default writes the per-user association and exits with 0 or 1, with no UI. Maintenance scripts live in scripts/ and are documented in docs/build-and-package.md.

What it does

• Opens Markdown the way Windows expects. Double-click, drag & drop, Open with, a second double-click while it is running (the file opens as a new tab in the existing window), or Ctrl+O.
• Markdown files look like documents. The .md type gets a page icon of its own in Explorer, not a copy of the app tile, and the "Open with" row keeps the app icon because that row represents the app.
• Reading first. Progress bar, outline drawer, find (match case / whole word), per-document reading position, a pinned section title (only once its heading scrolls out of view), and an image lightbox. No editing controls, because it is a viewer.
• Renders GitHub-flavoured Markdown: tables, task lists, alerts, footnotes, definition lists, autolinks — sanitised through an allow-list before it reaches the page.
• Syntax highlighting without a highlighter bundle. Fenced code is tokenised in Rust on the render path for the languages notes actually use; unknown languages are left alone.
• Several documents, one window. Tabs, each with its own scroll position, find query and document. The strip appears once a second document is open.
• Follows the file on disk. The open document is watched; edit it in another editor and the view updates, keeping your place.
• Yours to adjust. System/light/dark theme, text size, reading width, reading position, session restore, find defaults and remembered window geometry, all in one settings dialog.

Keyboard

Key	Action
Ctrl+O	Open a file
Ctrl+F	Find; Enter / Shift+Enter step through matches, Esc closes
Ctrl+B	Contents drawer
Ctrl+Tab / Ctrl+Shift+Tab	Next / previous document (wraps)
Ctrl+W	Close the document you are reading
Ctrl+R / F5	Reload from disk
Ctrl+Shift+L	Cycle system → light → dark
Ctrl + / - / 0	Text size up / down / reset
Ctrl + wheel	Text size, the same scale as above
J / K	Scroll a page down / up
Alt+C / Alt+W	Find: match case / whole word
Esc	Close the find bar, drawer, lightbox or settings

Inside the tab strip: ← → move between tabs, Home / End jump to the first and last, and a middle-click closes the tab under the pointer.

Requirements

• Windows 10 or Windows 11, x64.
• WebView2 runtime — preinstalled on Windows 11 and most Windows 10 machines; the installer fetches it when it is missing. A portable copy cannot install it, so a clean image without the runtime needs the installer first.
• Nothing else: no .NET, no Node, no browser.

Deliberate limitations

A viewer, by design: read-only, no printing or PDF export, no telemetry or account, no network requests at start-up, no auto-update and no plugin system. Multiple windows are also a non-goal — a window is a whole WebView2 process tree, so tabs carry several documents at flat cost.

Each of these is argued rather than assumed, together with the things that are missing for smaller reasons, in docs/limitations.md.

Documentation

Document	Covers
docs/architecture.md	Project layout, the Rust render path and IPC surface, and the three-file frontend.
docs/file-association.md	How the .md association, the ProgIds, the document icon and "Open with" are wired.
docs/build-and-package.md	Debug and release builds, the NSIS installer, registration scripts, the verification checklist and troubleshooting.
docs/performance.md	What the numbers mean, and where the <100 ms / <30 MB targets came from.
docs/limitations.md	What the app deliberately does not do, and why.
PERFORMANCE.md	The latest measurement, regenerated by scripts/measure.ps1.
ROADMAP.md	What is planned, what was rejected, and how a new idea gets considered.
CHANGELOG.md	Release history.
AGENTS.md	The maintenance contract: architecture notes, invariants and verification habits (written for coding agents, useful to anyone changing the internals).

Development

Most of the project can be worked on without Windows, Rust or the Tauri CLI.

Frontend and docs — Node only, and no install step:

node scripts/dev-server.js
# http://127.0.0.1:8123/preview/harness.html   the app, with a fake Tauri bridge
# http://127.0.0.1:8123/preview/tests.html    91 behavioural checks

Rust renderer and tests — any OS with Rust (on Linux this also needs Tauri's system packages; see CONTRIBUTING.md):

cargo test --manifest-path src-tauri/Cargo.toml     # 33 tests, 1 opt-in registry test
cargo run --manifest-path src-tauri/Cargo.toml -- samples/sample.md

Windows app and installer — needs Windows, WebView2 and the Tauri CLI:

npm install
npm run bundle

CI enforces the constraints as well as the tests: a frontend size budget (src/ ≤ 118 KB, app.js ≤ 70 KB), the front-end suite in a headless browser, cargo fmt --check, cargo clippy -- -D warnings and cargo test on Windows; on Ubuntu the same front-end suite runs in headless Chromium alongside cargo check --all-targets and cargo test, so neither the browser suite nor the Rust side depends on Windows.

Full walkthrough, including the file-association registration and the installer checks: docs/build-and-package.md.

Contributing

Issues and questions are welcome — use the issue templates for bugs and feature requests, and Discussions for questions and ideas. Two things worth knowing before proposing a change:

• The constraints are architectural. Three static files, no bundler or framework, a hard size budget, no new frontend dependencies, and read-only behaviour. A change that trades those away needs an explicit decision, not a patch.
• The roadmap says no on purpose. ROADMAP.md lists what is refused as well as what is planned; a feature there marked not planned has a reason attached.

The details — how to build, what CI enforces, what a pull request should contain — are in CONTRIBUTING.md. Participation is covered by the Code of Conduct.

Security issues: please report them privately through GitHub security advisories rather than in a public issue, as described in SECURITY.md.

Credits & licence

MD Viewer is created and maintained by N4OD.

It stands on other people's work: Tauri, pulldown-cmark, ammonia and notify. The Markdown dialect follows CommonMark plus GitHub's extensions, and the icon set is generated from scratch by scripts/make-icons.ps1.

Released under the MIT License © 2026 N4OD.