Markdown Runner

About

Markdown Runner enhances code blocks on any webpage — blogs, documentation, GitHub READMEs, and more. Every code block becomes interactive with just one click.

★ CODE EXECUTION
• Run JavaScript, TypeScript, HTML, and CSS code directly in the browser
• CSS blocks auto-generate matching HTML for instant visual preview
• Combined execution for consecutive HTML + CSS + JS blocks (great for tutorials)
• Sandboxed execution — your browsing is completely safe

★ SMART COPY
• One-click copy button on every code block
• Copies clean code only — no line numbers or UI artifacts

★ CODE DIFF
• Detect consecutive code blocks and compare them side by side
• Inline or split diff view with syntax highlighting

★ CODE FOLDING
• Long code blocks automatically fold with a configurable threshold
• Smooth expand/collapse with a "Show more (N lines)" button

★ LANGUAGE LABELS
• Automatically detects and displays the programming language
• Supports 40+ languages

★ LINE NUMBERS
• Optional line numbers for easy code reference
• Seamlessly integrates with existing page styles

★ MERMAID DIAGRAMS
• Render Mermaid code blocks as beautiful diagrams
• Supports flowcharts, sequence diagrams, Gantt charts, and more

★ JSON FORMATTER
• Interactive collapsible tree view for JSON/JSONC code blocks
• Click any value to copy it — shows the full JSON path
• Handles comments, trailing commas, and JSON fragments

★ FLOATING TABLE OF CONTENTS
• Auto-generated TOC from page headings
• Highlights your current reading position

★ READING PROGRESS BAR
• Thin progress bar at the top of the page
• Shows how far you've scrolled through the article

─── CUSTOMIZATION ───

• Toggle each feature independently from the popup
• Configure folding threshold, execution timeout, diff view mode
• Site whitelist/blacklist for granular control
• Light and dark theme support
• English and Chinese interface

─── PRIVACY ───

Markdown Runner processes everything locally. No data is collected or sent to external servers. Your code stays in your browser.

─── OPEN SOURCE ───

GitHub: https://github.com/2019-02-18/markdown-runner
Issues & Feedback: https://github.com/2019-02-18/markdown-runner/issues