Markdownify от Manikant Jha

Markdownify is designed to be offline-first. Markdown parsing, HTML sanitization, Mermaid rendering, and theme handling happen locally in your browser, so your document content does not need to be sent to a server for previewing.

There is no account, back-end, or analytics flow in this project. Once installed, the core preview experience works without a Markdown service watching over your shoulder: the page is transformed on-device, and the extension does not include network or telemetry code.