In short
A .md file is a plain-text document written in Markdown, a formatting syntax that uses characters like # for headings and ** for bold. Windows and macOS open it as raw text because they have no Markdown renderer; to read it formatted, drop it into a browser-based Markdown viewer, or open it in VS Code, Obsidian or on GitHub. It is safe to open and can be converted to PDF or Word in seconds.
| File type | Plain text, UTF-8, using Markdown syntax |
|---|---|
| Extension variants | .md, .markdown, .mdown, .mkd |
| Typical size | A few kilobytes; a book-length document is under a megabyte |
| Opens in | Any text editor (raw), or a Markdown viewer / editor (formatted) |
| Common sources | GitHub READMEs, Obsidian notes, Notion exports, AI assistant answers |
| Convert to | PDF, Word, HTML or plain text with the converters on this site |
| Safe to open | Yes — plain text cannot execute; viewers sanitise any embedded HTML |
What a .md file contains
A .md file is plain text. Open it in any text editor and you will see ordinary words with a few formatting characters mixed in: # before headings, ** around bold text, - before bullet points, and | between table cells. Those characters are Markdown, a lightweight formatting syntax designed so the raw file stays readable even without a renderer.
Because it is plain text, a .md file is tiny, opens anywhere, works with version control, and will still be readable in decades. That is why it has become the default for software documentation, note-taking apps and, more recently, the answers written by AI assistants.
Where .md files come from
| Source | What the file usually is |
|---|---|
| GitHub, GitLab, any code repository | README.md, CHANGELOG.md, CONTRIBUTING.md — project documentation |
| Obsidian, Logseq, Bear, Joplin, iA Writer | Your notes; each note is one .md file in a folder |
| Notion, Google Docs (export) | Documents exported as Markdown for use elsewhere |
| ChatGPT, Claude, Gemini | Answers saved or downloaded as Markdown |
| Static site generators (Hugo, Jekyll, Astro) | Blog posts and pages before they are built into HTML |
| Developer tools and CLIs | Generated reports, logs and help text |
Why it opens as raw text on your computer
Neither Windows nor macOS ships a Markdown renderer. Windows hands .md to Notepad; macOS hands it to TextEdit. Both show the file exactly as stored, formatting characters and all, because to the operating system it is a text file like any other. Nothing is wrong with the file — it simply needs software that understands the syntax.
How to open a .md file
| Method | Best for | How |
|---|---|---|
| Browser viewer (this site) | Reading a file someone sent you, once | Drop it into the Markdown viewer; nothing is uploaded |
| VS Code | Editing, especially for developers | Open the file, press Ctrl/Cmd+Shift+V for a preview |
| Obsidian | Ongoing notes and linked documents | Put the file in a vault folder |
| Typora, MarkText, iA Writer | A clean writing app | Open the file directly |
| GitHub | Files already in a repository | GitHub renders .md automatically |
| Notepad / TextEdit | Seeing or editing the raw text | Works, but shows the syntax rather than the formatting |
How to convert a .md file to something else
If the person you are sending it to does not use Markdown, convert it first. The Markdown to PDF converter produces a file anyone can open and print; the Markdown to Word converter produces a .docx they can edit and comment on. Both run in the browser and preserve headings, lists, tables, links and code blocks.
How to create a .md file
Any text editor will do: write the content, add the formatting characters, and save with a .md extension. For a live preview while you write, use the Markdown editor, and keep the Markdown cheat sheet open for the syntax.
Is a .md file safe to open?
Yes. A .md file is plain text and cannot contain executable code. The one caution is that Markdown allows raw HTML, so a file from an untrusted source could include a script tag; reputable viewers, including the one on this site, sanitise HTML before rendering it.