The short answer
An .md file is a plain-text document written in Markdown — a lightweight formatting language created by John Gruber in 2004. Instead of hidden formatting codes like Word uses, Markdown marks structure with visible characters: # Title makes a heading, **bold** makes bold text, - starts a list item.
Why do I keep receiving .md files?
Because software and AI tools love the format. README files on GitHub are markdown. Documentation is markdown. And most importantly today: ChatGPT, Claude, Cursor and other AI tools export their answers as .md files, since Markdown captures headings, tables and code without any proprietary format.
What's inside one?
Just text. If you open an .md file in Notepad you'll see readable content sprinkled with symbols:
# Quarterly Report
## Highlights
- Revenue **up 18%**
- New market: Japan
| Metric | Value |
|--------|-------|
| NPS | 62 |A markdown viewer turns those symbols into a formatted document — which is exactly what the tool at the top of this page does.
MD vs. other formats
| Format | Type | Best for |
|---|---|---|
| .md | Plain text + markup | Notes, docs, AI output |
| .docx | Binary/XML, rich | Office editing |
| .txt | Plain text | Raw notes, no structure |
| .html | Markup for browsers | Web pages |
How do I open it?
Scroll up and drop your file into the viewer — it renders instantly and can be exported to PDF or Word. For local apps and per-device instructions, see how to open MD files.