HTML

What this HTML tool does

Paste or open a .html file and the markup is rendered live inside a sandboxed <iframe> on the right side of the editor. It is meant for two everyday tasks: previewing a fragment of HTML (an email template, a snippet from a tutorial, a piece of generated output) without spinning up a local server, and editing markup with full syntax highlighting before downloading the result.

Why a sandboxed iframe?

The preview pane uses <iframe sandbox=""> — the strictest sandbox configuration the browser offers. Scripts, forms, top-level navigation, and same-origin access are all disabled. That means even if the HTML you paste contains an inline <script> or a tracking pixel, it cannot read the surrounding page, access cookies, or make network requests. This is the right default for inspecting untrusted markup pulled from emails, scraped pages, or AI output.

Common tasks

• Cleaning up generated HTML — reformat by hand, fix unclosed tags, strip inline styles, and re-download.
• Previewing email markup — most mail clients reject scripts anyway, so the sandboxed preview is a realistic approximation of what recipients will see.
• Sharing a quick prototype — paste in markup, refine the layout, then download the file and attach it to a ticket or pull request.

Tips

• External stylesheets and images load from their original URLs, so a preview of a page fragment may look different from the live site if it relies on relative paths.
• The editor preserves the encoding of the file you opened. If you opened a Korean or Japanese page that was saved as EUC-KR or Shift-JIS, the encoding-detection step handles it automatically.