First, what exactly is an .md file?
.md is the file extension for Markdown. Markdown is a plain-text format that uses simple symbols for formatting — for example, # for headings, - for lists, and **text** for bold.
The key point: Markdown files are plain text, so Notepad can indeed open them — but what you see is the "source code," not the nicely rendered layout. To see normal formatting, you need a tool that can "render" it. (For a quick intro to Markdown, see this 3-minute primer.)
In one sentence: .md files need a "rendering tool" to show formatted output. All three tools below can do it; the difference is convenience.
Method 1: Use a Markdown viewer (recommended)
If your need is simply "take a quick look at this file," the easiest way is to install a lightweight Markdown viewer like mdview.
How it works:
- Download the installer (about 1.6MB) and run it;
- During installation, it automatically registers the .md file association, so .md files get the mdview icon;
- From then on, double-click any .md file to open it instantly, press
Escto close — as simple as opening an image.
Its advantage is reading-focused: launch is nearly instant, no plugin loading, files render locally and aren't uploaded. If your daily routine involves reading READMEs, docs, and notes, this is the most convenient choice.
About the Windows security warning: The first time you run it, Windows may show "Windows protected your PC." This happens because the app doesn't have a commercial code signing certificate, not because it's actually risky. Click More info → Run anyway. mdview runs entirely locally and doesn't connect to any external server.
Method 2: Use a code editor (VS Code)
If you already code and have VS Code installed, you don't need anything extra to open .md files:
- Right-click the .md file → Open with → VS Code;
- Press
Ctrl + Shift + Vto open the preview panel and see the rendered result.
VS Code is powerful and lets you edit too. The trade-off is slower startup — to view a tiny document, you wait for the whole editor and plugins to load, usually 3–5 seconds. If you just want to read without editing, it's overkill.
Method 3: Browser + online tools
Don't want to install anything? Use an online Markdown preview site: copy-paste the file content (or drag the file) and the page renders it.
The upside is zero installation, good for temporary one-off viewing. But the downsides are clear:
- You have to manually copy-paste or drag every time, which is tedious;
- Local images in the document usually won't display;
- Pasting content into an unfamiliar site isn't great for privacy-sensitive documents.
Comparison of the three methods
| Comparison | Markdown viewer | VS Code | Browser online tool |
|---|---|---|---|
| Open speed | Instant | 3–5 seconds | Copy-paste needed |
| Double-click to open | ✓ Yes | Yes (needs default setup) | ✕ No |
| Local images | ✓ Supported | ✓ Supported | ✕ Usually not supported |
| Privacy | Fully local | Fully local | Uploaded to site |
| Can edit | Opens in editor | ✓ Powerful | Depends on site |
| Best for | Readers | Developers | Temporary viewing |
Conclusion: choose based on your needs
- Just want to read files quickly → Markdown viewer (mdview), double-click and done;
- Edit often or write code → VS Code, one tool for viewing and editing;
- Only view occasionally and don't want to install software → online tool, good enough for a one-off.
Tip: If you install mdview and later want to remove the .md file association, right-click in the preview window → Open settings → Unbind, or run the command mdview --unbind. You can restore it anytime.