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Overview
Paste HTML into this html viewer and see it rendered live in a sandboxed preview - not just the source code, the actual page - with a responsive width switcher, a captured console panel, and a lightweight linter, all instantly and all in your browser. Built for the moment you need to check how a pasted landing page or component actually looks and behaves, across screen sizes, without deploying anything first.
Best for: Checking a pasted landing page layout across screen sizes before shipping it
How to use this tool
- Paste your HTML. Drop in a full page or a snippet - scripts and styles work too.
- Check the linter warnings. Unclosed tags, mismatched tags, and duplicate IDs are flagged automatically.
- Preview across viewports. Switch between Desktop, Tablet, and Mobile widths to check the real layout.
- Debug with the console panel. console.log output and runtime errors from your scripts show up live below the preview.
Is there a free HTML viewer online that actually renders the page, not just the code?
Yes - this one renders your HTML, CSS, and JavaScript in a live sandboxed preview, not just a syntax-highlighted read of the source. Scripts run, styles apply, and the result looks the way it would in a real browser, entirely client-side with nothing ever uploaded anywhere.
That rendering happens inside an iframe locked down with sandbox="allow-scripts" and no allow-same-origin. If allow-same-origin isn’t set, the previewed content is treated as coming from a special origin that always fails the same-origin policy, blocking it from this site’s cookies, storage, and JavaScript APIs - so pasted scripts can run and be debugged, but they can’t reach anything of yours.
Pasting HTML that’s minified or inconsistently indented first? The HTML Formatter & Beautifier cleans it up before you preview it here, so what you’re debugging is readable markup, not a single unbroken line.
What does an HTML preview actually need to show you beyond a static render?
A single fixed-width render answers almost nothing about whether a layout actually works - this preview switches between Desktop, Tablet, and Mobile widths so CSS media queries and responsive rules genuinely re-evaluate at each size, the same way they would if you resized a real browser window. Since this preview renders pasted CSS too, running it through the CSS Formatter & Beautifier first makes it easier to spot exactly which rule is causing a layout issue. A captured console panel shows console.log/warn/error output and runtime errors from scripts running inside the preview, so broken JavaScript is visible immediately instead of a silently blank result. Debugging is also easier when the script isn’t minified in the first place - run it through the JavaScript Formatter & Beautifier first if it came out of a build step.
A lightweight linter also scans for unclosed tags, mismatched tags, and duplicate id attributes, listing them as non-blocking warnings above the preview - the specific mistakes that most often silently break a layout or a getElementById lookup, surfaced before you go looking for them.
Comparison
| Feature | What it does | When to use it |
|---|---|---|
| Live preview | Renders pasted HTML, CSS, and JS in a sandboxed iframe | Checking how a pasted page or component actually looks and behaves |
| Responsive switcher | Resizes the preview to Desktop, Tablet, and Mobile widths | Verifying a layout holds up across screen sizes |
| Console panel | Captures console.log/warn/error and runtime errors live | Debugging broken JavaScript in the pasted page |
| Linter warnings | Flags unclosed tags, mismatched tags, duplicate IDs | Catching markup mistakes before they break something |
Why use this tool
Actually check responsiveness
Switch between Desktop, Tablet, and Mobile widths instead of guessing how a layout will hold up.
Debug scripts, not guess
Captured console output and runtime errors show up live, so broken JavaScript is visible immediately.
Sandboxed by default
Scripts run in an isolated iframe with no access to this site or your data - safe to experiment.
Export when you’re done
Download the page as a .html file or copy it as a shareable data URI, no hosting required.
Frequently asked questions
Scripts do run, but only inside a sandboxed iframe using sandbox="allow-scripts" with no "allow-same-origin" - that combination means the preview gets an opaque, isolated origin with no access to this site’s cookies, storage, or parent page, and it can’t navigate the top-level page or escape the frame. That said, sandboxing limits what a script can reach, not what it can compute - a malicious script could still, say, try to phish via convincing-looking preview content, so you should still avoid pasting HTML from sources you don’t trust, the same caution you’d apply to running any unfamiliar code.
The Desktop/Tablet/Mobile buttons resize the preview iframe itself to 100%, 768px, and 375px respectively - common breakpoint reference widths - rather than just shrinking a screenshot, so CSS media queries and responsive layout rules in your HTML genuinely re-evaluate at each width, the same way they would in a real browser resized to that viewport.
No - it checks a specific, common set of issues (unclosed tags, mismatched open/close tags, duplicate id attributes) using a lightweight tag-stack scan, not a full HTML5 parser or validator. It’s meant to catch the mistakes that most often silently break a layout or a getElementById lookup, not to replace a complete markup validator for spec compliance.