Preview Markdown Instantly

Most browser previewers re-parse the whole document on every keystroke, which is why they stall on anything long. Mardna splits the document into top-level blocks — a paragraph, a list, a fenced code block — and re-renders only the block the caret is in. A ten-thousand-line document costs the same per keystroke as a ten-line one.

Syntax highlighting is worked out in the background, so colouring a large code block never blocks the keyboard, and rendered diagrams are remembered, so scrolling back over them costs nothing.

The default is a split view with a draggable divider: Markdown on the left, the typeset page on the right, scroll-synced so the two panes stay on the same passage. ⌘\ turns the split off and ⌘⇧P flips a single pane between editing and preview, which is the better arrangement on a narrow screen — on phones the two become tabs.

A floating table of contents tracks the headings on wide screens, every heading carries a copyable anchor link, and clicking an image opens it full-screen.

The preview is not an approximation of Markdown; it is the same pipeline that produces the exported file, so what you see is what ships.

• GitHub Flavored Markdown — tables, task lists, strikethrough, footnotes and autolinked URLs.
• Fenced code highlighted to editor standards, across hundreds of languages — the tag on the fence decides which.
• Mermaid diagrams — flowcharts, sequence diagrams, state and class diagrams — rendered from a mermaid fence and expandable to full screen.
• LaTeX math, inline and as display equations.
• GitHub alerts such as > [!NOTE] and > [!WARNING], with their icons.
• Raw HTML inside the Markdown, for the tags Markdown has no syntax for.

Math, raw HTML and diagram support load only when a document contains them, which is why the first paint is quick on an ordinary README.

The default theme follows GitHub's own Markdown rendering closely, so a README previewed here is a fair rehearsal of the repository page — heading sizes, table rules, code block treatment and alert styling included. Drop the file in, read it as a reader would, fix the table that broke, and push with some confidence.

When the document is not destined for GitHub, switch it to one of the typeset themes and the same source reads as a paper or an article instead.