HTML Online Viewer
Client-Side SandboxLive HTML, CSS & JavaScript preview. Everything runs locally — nothing is uploaded.
Why this viewer
A sandbox that respects your code
Client-side execution
No server logging, no uploads, complete privacy. Your snippets never leave the tab — safe for proprietary markup and client work.
Mobile-first responsiveness
A toggle-tab interface on small screens plus device-width emulation on desktop. Debug smartphone layouts from the phone itself.
Real-time DOM & script execution
Every keystroke re-renders through a debounced srcdoc injection. Inline CSS applies instantly and scripts execute in a safe sandbox.
Quick guide
How to use the HTML viewer
- 01
Paste your code
Drop any HTML snippet into the editor — full documents or fragments, with inline CSS and JavaScript included. Tab indentation works out of the box.
- 02
View the instant preview
The sandboxed preview re-renders live (~300ms debounce) as you type. On mobile, flip between the Code and Preview tabs with one tap.
- 03
Emulate device dimensions
On larger screens, constrain the preview to 375px (mobile), 768px (tablet), or full width to verify responsive breakpoints before shipping.
FAQ
HTML viewer questions
Does this tool send my HTML code to any server?
No. The HTML Online Viewer runs entirely inside your browser. Your code is rendered locally through an isolated iframe using the srcdoc attribute — no HTTP request carries your markup anywhere. You can verify this yourself by opening your browser DevTools network tab while typing: it stays silent.
Can I execute JavaScript and CSS inside this viewer?
Yes, fully. Inline <style> blocks style the preview instantly, and inline <script> blocks execute inside a sandboxed iframe (sandbox="allow-scripts") with an opaque origin. That means your scripts run for preview purposes but remain isolated from the rest of the site.
Why use this instead of opening a local HTML file on mobile?
Mobile operating systems make opening local .html files awkward: there is no straightforward file association, editors and browsers live in separate apps, and every tweak means re-saving and re-opening. Here you paste once and get a live preview with device-width emulation (375px, 768px, full width) in the same tab — no file juggling required.