What is an MD file, and how do you open one?

An MD file is a Markdown document. Markdown writes formatting into plain text: a few marks in front of and around the words say how they should look, and an app that understands them shows the formatted page. John Gruber, who created it, calls it an easy-to-read, easy-to-write plain text format.

Because it’s ordinary text, any text editor opens it, which is why you see the marks. The usual extensions are .md and .markdown.

• A pound sign starts a heading, and each extra one makes it a level smaller, down to six.
• Checkboxes and tables came later than Gruber’s original, from GitHub Flavored Markdown, which is why some apps leave them exactly as typed.
• It turns up everywhere because it’s quick to write and easy to pass around: Claude can export a document as Markdown, and programmers write their README notes in it.

Select the file in Finder and press the space bar: Quick Look shows the plain text, marks and all. TextEdit opens it the same way. Neither one shows the formatting.

• On macOS Tahoe 26 and later, Notes can bring the file in with File, Import Markdown. You get a formatted note, but it’s a copy inside Notes, so what you change there stays in Notes, not in the .md file.

A Windows 11 PC goes a step further. Right-click the file and choose Edit in Notepad, which newer updates put under App extensions. Recent versions of Notepad show Markdown formatted, with a button in the status bar that switches between Formatted and Markdown syntax. When it works, the pound signs disappear and the headings turn large and bold.

• The formatted view skips checkboxes and quotes. When the file has them, Notepad warns that switching views could change parts of your Markdown, and choosing Continue does change the text.
• If your Notepad only shows the marks, it’s an older one: Microsoft added the formatted view in version 11.2504, Windows Insiders first, and Notepad updates through the Microsoft Store.

For a fuller preview on Windows, a Mac or Linux there’s VS Code, Microsoft’s free code editor. Open the file and press Ctrl+Shift+V (⇧⌘V on a Mac): the formatted page takes the place of the text in the same tab. Ctrl+K V opens it beside the text instead.

• It’s built for programmers. A file you downloaded can open under a Restricted Mode banner, VS Code’s guard for files from places it doesn’t trust yet, and the preview leaves checkboxes as [x] and [ ] brackets.

Phones are where people get stuck. Tap an MD file in the iPhone’s Files app and you see the plain text with every mark in place. On a stock Android phone, the built-in Files app won’t open it at all. Neither comes with a way to show the formatting.

• The Android result comes from the Files app a stock Android phone ships with. Phones whose maker adds its own file manager weren’t part of this test.

Markdly is made for Markdown on Mac, Windows and Linux, and on iPhone, iPad and Android. It opens an MD file the way each device expects, shows it formatted, and saves your changes back into the same plain .md file.

• Mac
• Windows
• Linux

• iPhone
• iPad
• Android

Sign in with the same Bravely Account on each one.

Right-click the file, choose Open With, then Markdly. The buttons at the top switch between Visual for the formatted page, Markdown for the text, and Split for both, the text beside the page.

• Edit a line and save, and it’s still a plain .md file that any other editor can read: nothing is imported or converted.
• To open every .md file in Markdly with a double-click, select one in Finder, choose File, Get Info, pick Markdly under Open with, and click Change All.

Right-click the file and choose Open with: Markdly is on the list, and a click opens the file in it. To make it the app for every .md file, choose Choose another app instead, select Markdly and click Always. Markdly never makes itself the default; you choose it.

• You can also open Markdly and choose Open (Ctrl+O), or drag the file onto its window.

On an iPhone or iPad, open the file’s preview in Files again: with Markdly installed, its markd.ly button sits right under the text. Tap it, switch to Visual, and the headings, the checklist and the table appear as they’re meant to look.

On an Android phone with Markdly open, tap the file in Files and it goes straight into Markdly, in Visual. Change a line in the Markdown view, and save it back to the same file.

With the .deb package installed, Markdly appears in your file manager’s Open With menu for Markdown files, under the name Markdly.