HTML Viewer & Live Renderer
An HTML/CSS/JS playground renders pasted code in an isolated sandbox instead of just displaying it as text — so you see the actual result, interactive elements included. Paste HTML, CSS and JS and see an instant rendered preview, no signup or install.
1 Your code
Why a sandboxed preview beats copy-pasting into a file
Testing a small HTML/CSS/JS snippet usually means creating a throwaway file, opening it in a browser, and repeating that loop for every change — or reaching for a full code editor when all you needed was to see whether one layout idea actually works. A live, in-browser sandbox skips both: paste, see the result immediately, adjust.
The preview runs in an iframe sandboxed to allow scripts without allowing same-origin access, so pasted code — including code from a source you haven't fully vetted — can't read cookies, local storage, or anything else belonging to this site. That isolation is what makes it safe to try things quickly. If you're starting from an existing page's markup rather than writing from scratch, the HTML Formatter & Source Checker is the better starting point.
For example, pasting <button>Click me</button> in HTML and button { background: teal; color: #fff; } in CSS renders an actual clickable teal button in the preview — not just the code, the real thing.
How to use this tool
-
1
Add your code
Type or paste into the HTML, CSS and JS tabs. You can use any one of them on its own.
-
2
Watch the preview
The preview refreshes automatically a moment after you stop typing. Click "Run now" to refresh it immediately.
-
3
Test screen sizes
Switch between Desktop (full width), Tablet (768 pixels) and Mobile (390 pixels) to check responsive layouts.
-
4
Inspect the combined page
Open "View compiled HTML" to see the single document that merges your three tabs.
-
5
Open it full size
Click "Open in new tab" to view the result in a full browser window.
Common use cases
- Prototyping a component or layout idea before adding it to a real project.
- Checking CSS media queries at tablet and phone widths.
- Reducing a bug to a small snippet you can share with a colleague or on a forum.
- Previewing an HTML email fragment or third-party embed code.
- Learning HTML, CSS and JavaScript with instant visual feedback.
Tips and common mistakes
- Use full URLs for external files. Relative paths such as
/css/site.csspoint nowhere, because the preview has no server behind it. - Storage is blocked by design. The sandbox has no access to cookies or localStorage, so code that relies on them will throw an error here even if it works on your own site.
- Your code is not saved. Copy it somewhere before closing or reloading the page.
- Inline small images. To include an image without hosting it, turn it into a data URI with the Base64 Encoder / Decoder. The HTML, CSS and JS sandboxes guide explains how iframe sandboxing keeps previews isolated.
Frequently asked questions
It's actually rendered and executed inside a sandboxed iframe — your JavaScript runs for real. That's what makes this useful for testing interactive snippets, not just previewing static markup.
The preview runs inside an iframe sandboxed with only "allow-scripts" and "allow-modals" — notably without "allow-same-origin" — so it can't read cookies, localStorage, or anything else from frostrank.com, and can't navigate or interact with the parent page. It's the same isolation technique tools like CodePen and JSFiddle use.
Not in a built-in panel yet — open your browser's DevTools console while viewing this page and it'll show up there, since the preview runs in a real frame on the page, sandboxing aside.
No — this tool always assembles them the same way: your CSS is inserted in <head>, your HTML in <body>, and your JS runs after, once the DOM is ready.
Yes, completely free with no signup. Everything is rendered entirely in your own browser — nothing you paste is ever sent to a server.
Uses the same sandboxed-iframe isolation technique (scripts allowed, same-origin explicitly denied) as established code playgrounds — not a naive innerHTML injection that would expose this site's cookies and storage to pasted code.
Was this tool helpful?
Rate it and leave a comment — takes 10 seconds, and genuinely helps decide what to fix or build next.