Drag the .md file onto a browser-based Markdown viewer and it renders in a second — no app install, no upload. On macOS this beats the default behaviour of opening MD files in Xcode or a text editor, where you only see the raw markup.
Open the viewer — drag in your .md file →Your rendered document appears here.
Double-clicking an MD file on macOS usually lands you in a code editor or Quick Look's plain-text view: headings show as # symbols, tables as pipes, code as unstyled text. The lightest fixes, in order: a browser viewer — drag the file onto the page and it renders with styled headings, tables and highlighted code, nothing installed and nothing uploaded; Preview and Quick Look — Space-bar peeks show raw text only; an editor like VS Code — press Shift+Cmd+V for a built-in preview, worth it if you already have it; a dedicated Markdown app — only if you write Markdown every day. The browser route has two extra advantages on a Mac: the file is parsed locally in the tab, so private documents never leave the machine, and once the page has loaded the cached app shell keeps working with the network off — handy on a plane. Long READMEs and 10 MB documents render as quickly as short ones because there is no upload round-trip.
.md / README.md file onto the drop zone (or click to browse).