In short
A .md file is plain text written in Markdown, and Windows and macOS both open it in a text editor because neither associates the extension with a renderer. Drop the file onto this page and it is rendered in your browser — headings, tables, lists, links and code shown properly. The file is read locally and never uploaded, and you can switch between the formatted view and the original source.
| What .md means | A plain text file using Markdown formatting syntax |
|---|---|
| Opens | .md, .markdown, .mdown, .mkd and .txt files |
| Views | Reading (formatted) and Source (original text) |
| Renders | Headings, bold and italic, lists, task lists, tables, links, images, blockquotes, code blocks, footnotes |
| Also accepts | Markdown pasted directly onto the page |
| Export | Print or save as PDF, copy the source, or hand off to the converters |
| Privacy | Read in the browser with FileReader; never uploaded |
| Size limit | 10 MB |
What a .md file actually is
A .md file is a plain text file written in Markdown, a lightweight way of marking up formatting with ordinary characters. # at the start of a line means a heading, **text** means bold, - starts a bullet, and pipes make a table. It was designed so the raw file is still readable, but a long document full of symbols is tiring to read and tables are effectively unreadable.
Markdown is what README files on GitHub are written in, what Obsidian, Bear, Logseq and Joplin save notes as, and what ChatGPT, Claude and other assistants produce. So people meet .md files without ever choosing to use Markdown.
Why Windows and macOS don't open it properly
Neither operating system associates .md with a renderer. Windows hands it to Notepad and macOS to TextEdit, and both show the raw characters, because to them it is a text file like any other. Nothing is wrong with the file — it just needs something that understands the syntax.
Reading a file here
Drop the file onto this page, or click to choose it. The file is read by your browser with the FileReader API and rendered immediately. It is never uploaded, which matters because notes and drafts are often the most personal files people have. You can also paste Markdown directly onto the page.
Reading shows the formatted document. Source shows the original text, which is useful when you want to copy a snippet or check the exact syntax someone used.
Keeping a copy someone else can read
Use Print / PDF and choose "Save as PDF" to produce a file anyone can open, or Convert to move the same document into the Word, PDF or HTML converters.
If you open .md files often
A viewer in the browser is right for reading a file someone sent you. If you're writing Markdown regularly, a dedicated editor is better — VS Code, Obsidian and Typora all render as you type. On Windows you can also set a default app for .md so double-clicking opens your editor instead of Notepad.