HTML Runner
Paste and run HTML, CSS, and JavaScript in a live sandbox browser.
About HTML Runner
HTML Runner is an interactive, browser-based development sandbox engineered for web developers, designers, educators, and coding students who need to prototype, test, and render web code instantly. Instead of spinning up local servers, configuring build tools, or wrestling with complex editor setups, you can paste raw markup, embedded CSS stylesheets, and inline JavaScript into our dual-pane studio. The isolated sandbox executes your code immediately, providing a real-time responsive browser view, console logging output, and one-click file download.
How to Use HTML Runner
Paste your HTML markup or choose a template
Type or paste your HTML5 code into the left editor panel, or load sample presets such as Interactive App, Tailwind CSS Demo, or HTML5 Canvas Animation.
Run code and watch instant rendering
Keep Auto Run enabled to see live updates as you type, or click Run Code manually to execute scripts within an isolated iframe sandbox.
Test responsive viewports and check console logs
Switch between Desktop, Tablet (768px), and Mobile (375px) frame widths to verify responsive layouts, and inspect JavaScript console statements in the bottom log tray.
Download file or share with colleagues
Click Download .html to save a standalone web page, copy the source code to your clipboard, or create a unique share link to share your code sandbox with teammates.
Why Use HTML Runner: Common Use Cases
Front-End Prototyping and Rapid Experimentation
Frontend developers can quickly test UI components, CSS animations, flexbox layouts, and Tailwind CSS utility classes without creating temporary files in their local workspace.
Web Development Education and Coding Practice
Students and programming instructors can experiment with DOM manipulation, event listeners, and canvas drawing in a safe, zero-configuration environment.
Testing Generated AI Frontend Components
Developers utilizing AI coding models can paste generated components directly from our Screenshot to Code tool to preview and tweak styling before integrating into production repos.
Email Newsletter and Rich HTML Previewing
Marketers designing responsive email newsletter templates and transactional receipt cards can inspect how tables and inline CSS render across desktop and mobile screens alongside our Glassmorphism Generator.
HTML Runner Specifications
| Input Formats | HTML5 markup, Embedded <style> CSS, Inline <script> JavaScript, External CDN scripts |
|---|---|
| Output Formats | Sandboxed iframe render, Captured console logs, Single-file index.html, Shareable link |
| File Size Limit | No strict limit (dependent on device memory) |
| Processing Engine | Dedicated secure server worker |
| Data Retention | Deleted automatically within 15 minutes |
| Batch Processing | Single file processing |
Tips for HTML Runner
You can import modern external stylesheets like Tailwind CSS or Bootstrap by adding their official CDN script tags inside your
section.Click the Popout button in the top browser bar to open your code in a dedicated full-screen browser window for testing full-page layouts.
Use the console.log() function in your scripts to output debug statements; they are captured and displayed cleanly in the bottom log tray.
Test your responsive breakpoints by toggling between Desktop, Tablet, and Mobile viewport buttons to catch overflow issues early.
Frequently Asked Questions
Is it safe to run untrusted HTML and JavaScript code?
Yes. All execution takes place inside a sandboxed iframe with strict security isolation, preventing scripts from accessing your primary browser cookies or session storage.
Can I include external JavaScript libraries like Tailwind or jQuery?
Yes. Any CDN library accessible over HTTPS (such as Tailwind CSS, FontAwesome, or Three.js) can be loaded using standard script and link tags in your HTML.
Do I need to sign up or pay to run code?
No. HTML Runner is completely free on KiloToolbox with no account registration, no watermarks, and no usage limits.
Does this tool support CSS animations and HTML5 Canvas?
Yes. Full CSS keyframe animations, transition effects, Canvas 2D, and WebGL rendering are supported natively by your browser engine.
How does the Console Logs drawer work?
Our sandbox intercepts console.log messages produced by your embedded scripts and pipes them directly to the console tray below the preview window for easy debugging.
Can I share my live HTML snippet with someone else?
Yes. Click the Share button to generate a unique link. Anyone with the URL can view your code and test the live interactive preview.