What is markdown-online?

Markdown Online is a free browser-based tool for writing, previewing, converting, and exporting Markdown, the plain-text formatting style used constantly in AI prompts and responses. Instead of bouncing between ad-heavy online converters or heavy desktop apps like Obsidian or VS Code just to clean up or convert a piece of Markdown, this puts everything in one page. Nothing you write or paste ever leaves your machine, there is no signup, and there are no ads. The editor gives you a live side-by-side preview with optional scroll syncing, a find and replace bar, a collapsible formatting toolbar, and a status bar showing word count, character count, and an estimated token count for use with AI models. It supports numbered section headings, smart list behavior where pressing Enter continues bullet or numbered lists automatically, and a clickable document outline sidebar for jumping between headings. You can keep multiple named documents at once, each saved automatically in your browser's local storage. Beyond editing, it can open Markdown files from your device or import from HTML, CSV, or JSON and convert them into clean Markdown. It can export to Markdown, HTML, or PDF, and offers two ways to move content into Word: downloading a real Word document with proper editable heading styles, or copying a quick formatted version to paste directly into Word or Google Docs. It also renders inline math, Mermaid diagrams, and database schema diagrams written in DBML, complete with tables, keys, and relationship lines, along with a thumbnail strip for jumping between diagrams in a long document. Code blocks are syntax highlighted in roughly 35 languages both in the editor and the preview. All conversions run using open-source JavaScript libraries loaded directly on the page, so no data is ever sent to a server. This is aimed at anyone who regularly writes, edits, or converts Markdown, from developers to writers working with AI tools, who want a single reliable page for the whole workflow. It is released under the GPL-3.0 license and can be tried instantly at its GitHub Pages site.