Markdown basics
What is a Markdown file, and how do I open one on Windows?
You have been handed a file ending in .md, perhaps by a coding agent, a colleague or a download from GitHub. Here is what it is, why it looks the way it does, and the ways to read it on Windows.
Published 2026-10-17. Product details checked against Nice Markdown 1.0.4.
What is Markdown?
Markdown is a way of writing formatted text using nothing but ordinary characters. Instead of clicking a Bold button, you put two asterisks around a word. Instead of choosing Heading 1 from a menu, you start the line with a hash sign. A Markdown file is a plain text file that uses these marks, and it usually has the extension .md (sometimes .markdown).
A short example:
# Weekly report
The build is **green** and two tasks remain.
- [x] Update the dependencies
- [ ] Write the release notes
See the [full plan](plan.md) for details.Shown as a document, that becomes a heading, a sentence with one bold word, a two-item checklist with the first item ticked, and a link. The marks are simple enough to type by hand and simple enough for a program to produce.
Markdown was created by John Gruber in 2004. There is a core set of rules that every tool agrees on, plus common extensions. The most widely used set of extensions is GitHub Flavored Markdown (GFM), which adds tables, checklists and a few other things. Most tools today support GFM.
Why do so many things use .md files?
Three reasons. Markdown is plain text, so it opens in any editor on any system, works with version control such as Git, and will still be readable in twenty years. It is quick to write, so it is the default for README files, documentation and notes. And large language models have read an enormous amount of it, so coding agents such as Claude Code, Codex and GitHub Copilot write their plans, reports and instruction files in Markdown without being asked.
If you work with coding agents you will meet files like README.md, AGENTS.md, CLAUDE.md, PLAN.md and TODO.md. They are all ordinary Markdown. Our guide on reading the Markdown that coding agents write goes into what each one is for.
How to open a .md file on Windows
Because it is plain text, almost anything can open a Markdown file. The question is whether you see the raw marks or a formatted document.
| Open it with | What you see | Good for |
|---|---|---|
| Notepad | The raw text, marks and all | A quick look, or a tiny edit |
| Visual Studio Code or another code editor | The raw text, with an optional preview pane beside it (in VS Code, press Ctrl+Shift+V) | Developers who are already in the editor |
| GitHub, GitLab or a similar website | A formatted, read-only page | Files that live in an online repository |
| Microsoft Word | The raw text, which Word will try to autocorrect | Not recommended; saving from Word can change the file |
| A Markdown viewer or editor such as Nice Markdown | A formatted document you can read and edit | Reading long plans and reports comfortably, and making changes without learning the marks |
If you only need to read a file once, Notepad or your browser's preview on GitHub is fine. If Markdown files arrive regularly, a dedicated viewer or editor saves a lot of squinting, especially for tables and long checklists.
Source view and document view
Every Markdown tool shows the file in one of two ways. The source view is the raw text with all the marks visible. The document view (also called preview or rendered view) shows the formatting those marks describe, with no symbols in the way. Code editors usually show source with a preview beside it. Nice Markdown opens the document view first, with a Source view one click away, and lets you make changes directly in the document.
.md, .markdown, .mdx and .txt
.mdand.markdownare the same thing: a Markdown file..mdxis Markdown with embedded code components, used by some website frameworks. Ordinary Markdown tools will show the code parts as text..txtfiles sometimes contain Markdown too. Renaming the file to.mdlets Markdown tools recognise it.
Nice Markdown opens .md and .markdown files saved as UTF-8, which is the standard text encoding and what nearly every tool produces.
Common questions
Is a Markdown file safe to open?
A Markdown file is text. It cannot run a program on its own. As with any document, be careful with links inside it if you do not know where the file came from.
Is Markdown the same as HTML?
No, but they are related. HTML is the language web pages are written in and is fiddly to write by hand. Markdown is a friendlier shorthand that tools convert into HTML (or into a document view) when they display it.
Can I convert a Markdown file to Word or PDF?
Many tools can. Nice Markdown can print a file or export it as a PDF, including its tables and diagrams. Converting to a Word document needs a separate tool such as Pandoc.
Why does my file show odd symbols like # and * everywhere?
You are looking at the source view. Open the file in something that shows the document view, or switch to the preview in your editor, and the symbols become headings, bold text and lists.