Markdown + Mermaid Renderer

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Preview

Free Online Markdown & Mermaid.js Renderer

A fast, privacy-first Markdown renderer with built-in Mermaid.js diagram support. Paste or type Markdown on the left and watch a live preview appear on the right. Everything runs entirely in your browser — no account, no tracking cookies, no advertisements, no data ever leaves your device. Use it to preview README.md files, draft documentation, sketch architecture with flowcharts, or check how GitHub will render your Markdown before you commit.

What it does

Markdown live preview — GitHub-flavored Markdown renders as you type, with headings, lists, tables, code blocks, links and images.
Mermaid.js diagrams — render graph, flowchart, sequenceDiagram, classDiagram, stateDiagram, erDiagram, gantt, journey, pie, mindmap and timeline diagrams inline inside Markdown code fences.
Auto-render — the preview updates automatically on every keystroke and on paste, with lightweight debouncing to keep typing smooth.
Upload .md files — drag a Markdown file onto the editor or use the Upload button to open local files.
Download .md files — export your edited Markdown with one click (or Ctrl/Cmd + S).
Resizable split panes — drag the divider to give the editor or the preview as much room as you need.
Mobile responsive — panes stack vertically on small screens so it stays usable on a phone.
Secure by design — all HTML output is sanitized with DOMPurify to block XSS, and there is no server-side code at all.

Use cases

Preview a README.md before pushing to GitHub or GitLab.
Draft technical documentation with embedded Mermaid architecture and sequence diagrams.
Quickly check Markdown table syntax without spinning up a repo.
Convert Markdown notes into readable HTML for a quick glance.
Teach or learn Markdown and Mermaid syntax with instant visual feedback.
Prototype flowcharts, Gantt charts and ER diagrams directly in Markdown.

How to use Mermaid diagrams

Put a Mermaid diagram inside a fenced code block marked mermaid:

```mermaid
flowchart LR
    A[Markdown] -->|parsed| B(marked.js)
    B --> C{Mermaid block?}
    C -->|yes| D[Mermaid.js]
    C -->|no| E[HTML]
    D --> E
    E --> F((Live preview))
```

Supported diagram types include flowchart/graph, sequenceDiagram, classDiagram, stateDiagram, erDiagram, gantt, journey, pie, mindmap, timeline, gitGraph and C4Context.

Privacy & security

This tool is fully client-side: there is no backend that receives your text. Your Markdown never leaves your browser. There are no tracking cookies, no analytics scripts, and no ads. The page loads three open-source libraries from a CDN (marked.js, Mermaid.js and DOMPurify) and then works offline against your input. Because there is no server, there is no server-side attack surface: malicious Markdown can only affect the browser tab it was pasted into, and DOMPurify strips dangerous HTML before it ever reaches the preview.

Frequently asked questions

Is this Markdown renderer free?

Yes. It is 100% free, has no login, no paywall and no usage limits.

Does it store my Markdown?

No. There is no database and no server. Your content lives only in your browser tab. Closing the tab discards it, so download anything you want to keep.

Does it use tracking cookies or analytics?

No. There are no tracking cookies, no analytics scripts and no advertising networks loaded. The only third-party requests are to a CDN for the three open-source rendering libraries.

Can I use Mermaid diagrams?

Yes. Wrap the diagram source in a fenced code block tagged mermaid (three backticks followed by the word mermaid) and it will render inline in the preview.

Which Markdown flavor is supported?

GitHub-Flavored Markdown (GFM) via marked.js: tables, task lists, strikethrough, fenced code blocks, autolinks and more.

Does it work offline?

Once the three CDN libraries have been cached by your browser, the page works offline. The app itself has no network calls.

Is my data sent to a server?

No. All rendering happens locally in your browser. No Markdown content is ever transmitted over the network.