Markdown Runner

Enhance Markdown code blocks on any webpage — copy, run, diff, line numbers, folding, TOC and more.

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