HTML Viewer

How it works

Paste any HTML into the code pane and the viewer renders it live in the page below, updating as you type. Drag the separator between the code and the page up or down to give either side more room. The preview runs inside a sandboxed iframe — an isolated frame the rendered content can't escape — so the HTML you paste can't touch this page, your cookies or your files. A live counter shows the size of your markup in characters and kilobytes.

Why the preview is sandboxed

Rendering untrusted HTML on a normal page would be risky: scripts could read cookies, reach into the parent page or fire network requests. The viewer's preview frame gets a fully isolated origin, so pasted markup is rendered exactly as a browser would display it, but confined — it can't access anything outside its box. JavaScript is switched off by default; tick Enable JavaScript in preview if you need to test dynamic behaviour, and the frame re-renders with scripting allowed while staying sandboxed.

What people use it for

Previewing an HTML email before sending it, checking a markup snippet copied from a tutorial, testing how a landing-page block will look without spinning up a project, learning how tags render, or quickly inspecting HTML stripped out of a page. Since everything runs locally, you can safely paste private or unfinished work — nothing is transmitted or stored.

How to preview your HTML

Paste your markup into the code pane and the preview below refreshes by itself a fraction of a second after you stop typing — you don't press a button or reload the page. Drag the horizontal handle between the code and the preview to give either side more room, which is handy when a block is tall or you want to read its source while inspecting the result. Tick Enable JavaScript in preview if your snippet needs scripts to run, and the frame will re-render with scripting allowed while staying sandboxed. A live counter beside the checkbox reports the current size of your markup in characters and kilobytes, so you can gauge how heavy a document is at a glance.

A concrete example

Say you're building a newsletter and someone hands you a chunk of table-based HTML for the header. Paste it into the textarea: the header appears in the frame below exactly as a mail client would lay it out, color and padding included. Spot a misaligned cell, fix the <table> row in the code pane, and the frame updates on its own. Then tick Enable JavaScript in preview to check the tracking pixel or a hover effect that relies on a script. You never leave the page, open a local file, or upload anything — the whole check happens in your browser.

What to expect

The tool deliberately keeps its surface small: a plain textarea, a draggable divider, an iframe preview, a size counter, and a single checkbox to toggle JavaScript. Everything is rendered client-side in an isolated sandboxed frame, so behavior matches a real browser as long as the markup doesn't depend on a server. Inline styles and <style> blocks work normally; external resources load only if the browser can reach them. There is no defined size limit, so very large documents still render, just more slowly. Because the preview runs on your machine, nothing you paste is transmitted or stored anywhere.

Common problems and fixes

My images or fonts don't show. The preview is sandboxed with an isolated origin, so assets that need permissions or a logged-in session won't load — inline the images or use fully public URLs. My script does nothing. JavaScript is off by default for safety; tick Enable JavaScript in preview to allow it. The preview is blank. Check for an unclosed tag or a CSS rule that hides the whole body — the code pane still shows your markup, so a quick look at the closing tags usually reveals the fault. The frame looks different from my site. The preview shows your HTML with the browser's default styling, exactly one self-contained document, so CSS baked into your site's surrounding page won't apply unless you paste it too.

Frequently asked questions