Markdown Viewer

Live: spskelly.github.io/markdown-viewer
Repo: GitHub

What It Does

A lightweight PWA that registers as your system’s default .md file handler. Install it from the browser, set it as default, and double-clicking any markdown file renders it instantly, no editor, no terminal, no internet required.

Features

• System file handler, registers for .md and .markdown files via the File Handling API (Chromium)
• Tabbed viewing, open multiple files simultaneously and switch between them
• Syntax highlighting, 100+ languages via highlight.js
• Mermaid diagrams, flowcharts, sequence diagrams, Gantt charts rendered inline
• Dark/light mode, Ctrl+D to toggle, preference persisted
• Drag and drop, drop files directly onto the window
• Keyboard shortcuts, full shortcut set accessible via ?
• Print-friendly, clean print stylesheet
• Offline, service worker caches all assets after first visit

Why It Exists

There isn’t a good lightweight, dedicated markdown viewer out there. Most options are heavy editors, clunky browser extensions, or terminal tools. This fills the gap, double-click and get instant rendering.

Technical Details

The entire app is 5 files: index.html, app.js, styles.css, manifest.json, service-worker.js. ~1,700 lines total. No build step, no bundler, no framework. Vanilla JavaScript with the Web File Handling API for system integration and a cache-first service worker for offline support.