What is GitHub Flavored Markdown (GFM)?

GitHub Flavored Markdown is an extension of the standard Markdown specification, developed and standardized by GitHub. It adds several powerful features that the original Markdown lacks: tables with column alignment, task lists with checkboxes, strikethrough text (~~like this~~), fenced code blocks with language identifiers for syntax highlighting, and automatic URL linking. GFM is widely supported across platforms and has become the most practical Markdown dialect for developers and technical writers.

Does it support tables and task lists?

Yes. The Markdown Previewer fully supports GitHub Flavored Markdown, which includes tables (with headers, column alignment via colons, and pipe-separated cells) and task lists (using - [x] for completed items and - [ ] for pending items). You can see both in action by clicking "Load Example" to load a sample document that demonstrates all supported features.

Can I export to HTML?

Yes. You can export your rendered Markdown in two ways: use "Copy HTML" to copy the sanitized HTML output to your clipboard for pasting into other applications, or click "Download .html" to save a standalone HTML file with embedded CSS styling that opens in any browser. You can also download the raw Markdown as a .md file.

Is the preview sanitized for security?

Yes, absolutely. All rendered HTML is passed through DOMPurify, a battle-tested HTML sanitizer. It strips script tags, event handlers (like onclick, onerror), javascript: protocol links, and other XSS attack vectors. This means you can safely paste Markdown from any source without worrying about malicious code. Only safe HTML tags and attributes are allowed through.

What's the maximum input size?

The Markdown Previewer accepts input up to 500KB (approximately 500,000 characters). This is more than enough for most documents, including lengthy README files, comprehensive documentation pages, and long blog posts. If you exceed this limit, the tool will display an error message. Since all processing happens client-side, the practical limit also depends on your device’s available memory.

Does it support custom CSS?

The preview area uses standard prose styling that adapts to light and dark themes. While you cannot inject custom CSS directly into the preview, you can export the HTML file and add your own styles. The exported HTML includes a basic stylesheet that you can easily customize or replace with your own CSS framework (like Tailwind, Bootstrap, or your own styles).

Can I use it offline?

Yes. Since the Markdown Previewer runs entirely client-side, it works offline once the page has been loaded. All Markdown parsing, HTML rendering, and sanitization happen in your browser using JavaScript. There are no server calls during processing. This makes it perfect for working on documentation while traveling, in meetings, or anywhere with unreliable internet access.

Does it work on mobile devices?

Yes. The tool is fully responsive. On desktop and large screens, you get a split-pane layout with the editor on the left and the preview on the right. On mobile and small screens, it switches to a tabbed view where you can toggle between "Editor" and "Preview" tabs. All features — including statistics, table of contents, copy, and download — work on mobile devices.

🛠️DevToolsHub

Markdown Previewer

Preview Markdown in real-time with GitHub-flavored styling.

What is Markdown Previewer?

Markdown is a lightweight markup language created by John Gruber in 2004. It uses plain text syntax to create formatted documents — headings, bold and italic text, lists, links, code blocks, tables, and more — without the complexity of HTML. Markdown has become the de facto standard for writing on the web, powering README files on GitHub, documentation sites, blog platforms like Jekyll and Hugo, forum posts on Reddit, chat messages in Slack and Discord, and countless note-taking apps.

GitHub Flavored Markdown (GFM) is an extension of the original Markdown specification, standardized by GitHub. It adds powerful features that have become essential for modern technical writing: tables with column alignment, task lists with checkboxes, strikethrough text, fenced code blocks with language-specific syntax highlighting, and auto-linking of URLs. GFM is widely supported across tools and platforms, making it the most practical Markdown dialect for developers and writers alike.

A Markdown Previewer lets you write Markdown in one pane while seeing the rendered output in real time. This is invaluable because Markdown syntax can be tricky to get right — especially for complex elements like nested lists, tables, and code blocks. A live preview eliminates the guesswork: you see exactly how your formatted document will look before publishing it. Whether you’re writing a GitHub README, drafting documentation, composing a blog post, or formatting a comment, a previewer ensures your Markdown renders the way you intend.

Common use cases include: writing and reviewing GitHub README files, creating documentation for open-source projects, drafting blog posts for static site generators, formatting Slack and Discord messages, previewing comments before posting, learning Markdown syntax, converting Markdown to HTML for email newsletters, and checking that complex tables and code blocks render correctly. Whether you’re a developer documenting an API, a technical writer creating a user guide, a blogger drafting a post, or a student formatting notes — a Markdown previewer streamlines the writing workflow.

DevToolsHub’s Markdown Previewer runs entirely in your browser. Your content never leaves your device, ensuring complete privacy. It supports the full GFM specification, sanitizes HTML output to prevent XSS attacks, provides live statistics (word count, reading time, line count), and generates a table of contents from your headings. You can export your work as Markdown or a standalone HTML file — all without installing any software or creating an account.

How to Use Markdown Previewer

Type or paste your Markdowninto the editor pane on the left. You can also click “Load Example” to start with a sample document that demonstrates all supported features.
Watch the live preview update automatically on the right as you type. The preview renders with a 200ms debounce to keep things smooth even with large documents.
Check your statistics — word count, character count, line count, and estimated reading time appear below the editor in real time.
Toggle the Table of Contentsby clicking “Show TOC” to see a navigable list of all headings in your document, with indentation matching heading levels.
Copy the HTMLusing “Copy HTML” to grab the rendered, sanitized HTML output for use in other applications.
Download your work— save as a Markdown (“.md”) file or as a standalone HTML file with embedded styling, ready to open in any browser.

Supported Markdown Features

Headings— All six levels (H1–H6) using the#syntax.
Text formatting — Bold (**text**), italic (*text*), and strikethrough (~~text~~, GFM).
Inline code — Use backticks for`code`snippets within sentences.
Fenced code blocks — Triple backticks with optional language identifier for syntax hints.
Links — Both inline ([text](url)) and reference styles.
Images — Inline image syntax (![alt](url)) with alt text.
Lists — Ordered (numbered) and unordered (bulleted) lists, including nested lists with proper indentation.
Task lists (GFM) — Interactive checkboxes with- [x]and- [ ]syntax.
Tables (GFM) — Full table support with headers, column alignment, and pipe-separated cells.
Blockquotes — Prefixed lines with>for quoted content.
Horizontal rules — Three or more hyphens, asterisks, or underscores create a divider.
HTML passthrough — Safe HTML tags are rendered (scripts and event handlers are stripped for security).

Markdown Tips & Best Practices

Leave a blank line before and after block elements (headings, lists, code blocks, blockquotes). Markdown parsers need blank lines to distinguish block-level elements from inline content.
Use fenced code blocks (```) instead of indented code blocks — they’re more readable and support language hints for syntax highlighting.
Prefer reference-style links for long documents with repeated URLs. They keep your text readable in source form.
Use heading levels hierarchically — start with a single H1, use H2 for major sections, H3 for subsections. This improves accessibility and generates a cleaner table of contents.
Keep table columns aligned in source for readability — pipe characters should line up vertically.
Add alt text to all images— it’s good for accessibility and SEO, and shows up if the image fails to load.
Avoid raw HTML when possible— Markdown syntax is more portable and readable. Only use HTML for things Markdown can’t do (like buttons or iframes, which are sanitized here for security).

Features

Live split-pane preview — See your rendered Markdown update in real time as you type, with a 200ms debounce for smooth performance.
GitHub Flavored Markdown (GFM) — Full support for tables, task lists, strikethrough, fenced code blocks, and auto-linked URLs.
XSS-safe output — All HTML output is sanitized with DOMPurify, stripping script tags, event handlers, and other dangerous content.
Real-time statistics — Word count, character count, line count, and estimated reading time update instantly as you type.
Table of Contents — Automatically generated from your headings, with proper indentation and URL-friendly anchor links.
Export options — Download your document as a Markdown file or as a standalone, styled HTML file ready for any browser.
Copy HTML to clipboard — Grab the sanitized HTML output with one click for pasting into other applications.
Mobile-friendly tabbed view — On small screens, switch between Editor and Preview tabs instead of a split layout.
100% client-side (privacy-first) — All rendering and sanitization happens in your browser. Your content never touches a server.
Dark mode — The preview area and editor both support dark and light themes, following your system preference.

Example: Markdown Source vs. Rendered Output

Here’s a quick example showing how Markdown syntax translates to rendered HTML:

Markdown Source

Rendered Output

Shopping List

Milk
Eggs
Coffee
Bread

Recipe Link

Check out this recipe!

Frequently Asked Questions