HTML Previewer

Paste HTML and instantly see it rendered live in a safe, sandboxed preview. Free, instant and private — your code is rendered right in your browser and never uploaded to a server.

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The preview runs in a sandboxed <iframe> with a unique origin, so scripts in your code cannot read your cookies, storage or this page. Untick Run JavaScript to preview markup and CSS without executing any scripts.

How to use the HTML previewer

  1. Paste your HTML. Type or paste a full HTML document or a fragment of markup into the editor on the left.
  2. Watch it render live. The preview on the right updates automatically as you type, showing exactly how the page looks in a browser.
  3. Copy or download. Use Copy HTML to grab the code, or Download .html to save it as a ready-to-open web page.

About this tool

This free HTML previewer lets you test snippets, learn HTML and CSS, and check how markup renders without creating files or setting up a code editor. It is ideal for students, bloggers editing rich-text HTML, developers debugging email templates, and anyone who wants to see the result of a tag, style rule or small script straight away. Both full documents (with <!DOCTYPE>, <head> and <body>) and bare fragments render correctly.

Everything runs locally in your browser — your code is never uploaded, stored or logged. The preview is rendered inside a sandboxed iframe that is isolated to its own origin, which means any JavaScript in your HTML cannot access this page, your clipboard or your browsing data. That makes it safe to paste code you do not fully trust, and the tool keeps working offline once the page has loaded.

Frequently asked questions

Does the preview run JavaScript?

Yes, by default. Scripts run inside a sandboxed iframe that has its own isolated origin, so they can render your page but cannot read cookies, local storage or anything else on 123Tool.online. Untick the Run JavaScript box if you only want to preview HTML and CSS.

Is my HTML uploaded anywhere?

No. The code is rendered entirely in your browser using an iframe. Nothing is sent to a server, so your markup stays completely private and the tool works even without an internet connection.

Can I preview just a fragment instead of a full page?

Absolutely. You can paste a complete document or a single snippet like <button>Hi</button>. The browser wraps loose markup in a document automatically, so both render the same way.

Why can't the preview load external images or fonts?

References to files on the internet will load normally if you are online, but they must use full https:// URLs. Relative paths like images/logo.png have nothing to resolve against inside the preview, so use absolute URLs or inline data: URIs instead.