.md File Extension

What kind of file is a .md?

A .md file is a plain-text document written with Markdown, a lightweight markup syntax. Punctuation such as #, *, and backticks can express headings, emphasis, lists, links, and code while leaving the source readable in an ordinary text editor.

The registered MIME type is text/markdown. RFC 7763 lists .md and .markdown as filename extensions and specifies no magic number, so software generally identifies a Markdown file from its name or media type rather than a unique byte signature.¹

Markdown is a family of related syntaxes, not one perfectly uniform format. CommonMark defines a precise core syntax, while GitHub Flavored Markdown adds features such as tables, task-list items, strikethrough, and autolinks.²³

How do I open a .md on my computer?

For editing and a rendered preview, use Visual Studio Code, Obsidian, Typora, or another Markdown editor. Visual Studio Code supports .md files out of the box and can show the source and rendered preview side by side.⁴

Any plain-text editor can open the source:

• On Windows, use Visual Studio Code or Notepad.
• On macOS, use Visual Studio Code or TextEdit in plain-text mode.
• On Linux, use Visual Studio Code, Kate, GNOME Text Editor, Vim, or Emacs.
• On iOS and Android, use a Markdown editor or a text-editing app that can access the file.

GitHub renders .md files in repositories and supports its own Markdown extensions. A document that looks right on GitHub can render differently in a CommonMark-only tool, especially if it uses tables, alerts, task lists, or embedded HTML.³⁵

Poly support for .md

Poly recognizes the .md suffix, opens the document in a code-friendly editor with syntax highlighting, and indexes its readable content for exact and semantic search. The Poly agent can read the text and reason about headings, lists, links, and code examples.

Poly shows the Markdown source rather than promising that every flavor-specific feature will render like its original application. Linked images and remote resources may also depend on their locations and access permissions.

History of .md

John Gruber introduced Markdown on March 15, 2004 as a text-to-HTML tool and a readable plain-text writing syntax.⁶ The short .md suffix became one of its common filename conventions alongside .markdown. In March 2016, RFC 7763 registered text/markdown and formally listed both extensions.¹

The ecosystem later developed multiple dialects. CommonMark set out to remove ambiguities through a detailed specification and test suite, while GitHub Flavored Markdown built on CommonMark for repository documentation and collaboration.²³

Working with .md and alternatives

Keep Markdown portable by using UTF-8, a consistent flavor, relative links for files that travel together, and fenced code blocks with language labels. Preview the document in its destination before publishing.

Markdown can contain raw HTML or links with unsafe destinations. Treat files from untrusted sources as content to inspect, and use a renderer that sanitizes generated HTML. RFC 7763 recommends analyzing and sanitizing or blocking the output markup because different processors may interpret the same source differently.¹

Choose another format when the goal changes:

• .txt for unformatted text with the widest basic compatibility.
• HTML for a self-contained web page with controlled structure and styling.
• PDF for fixed layout intended to look consistent when shared or printed.
• DOCX or ODT for tracked changes, rich page layout, and office collaboration.

Conversion to HTML or PDF can preserve the rendered result, but may discard comments, frontmatter, or flavor-specific behavior. Keep the .md source when future editing and version-control-friendly diffs matter.