Open a browser-based MD viewer and drag the .md file onto the page — it opens and renders as a formatted document in about three seconds. No install, no account, no upload: the file is parsed on your device, not sent to a server.
Open the viewer — drag in your .md file →An MD file is plain text, so anything that reads text can open it — the difference is whether you see the raw markup or the rendered page. From fastest to heaviest: (1) a browser viewer — drag the file in, headings/tables/code render instantly, nothing installed, works for READMEs and one-off files; (2) a source-code editor like VS Code — press Ctrl+Shift+V for the built-in preview, good if you already have one installed; (3) a dedicated Markdown app — Typora or similar, worth it only if you write Markdown daily; (4) Notepad or TextEdit — always works, but you read # and ** symbols instead of formatted text. One rule that matters more than the tool: if the file is private, keep the opening local. Server-based converters upload your document before rendering it; a viewer that parses in the browser tab never sends it anywhere, and after the first load the cached app shell keeps working offline — useful on a plane or in a meeting room with dead Wi-Fi.
.md / README.md file onto the drop zone (or click to browse).