OPERAVA · Developer tools

Write HTML. See the result.

Edit a local HTML document and preview the result in a sandboxed frame without sending your code to a server.

HTML code editor with colored syntax and pencil

Import HTML file

HTML source

<!doctype html>
<html lang="en">
<head><meta charset="utf-8"><title>Hello</title><style>body{font-family:sans-serif;padding:2rem;color:#4b1675}h1{color:#a000f0}</style></head>
<body><h1>Hello OPERAVA!</h1><p>Edit the HTML and select Update preview.</p></body></html>

Sandboxed preview

The preview blocks external resources and forms. JavaScript runs in an isolated origin; only preview trusted code.

Sandbox limitations: Previewed HTML is isolated from the parent site and network access is restricted. Do not enter secrets or paste unknown scripts; a downloaded HTML file may behave differently outside this sandbox. Local drafts stay on this device unless you download them.

Source editing tools

Counting lines and characters…

Find textReplacement

These actions edit the browser-local source only. Choose Update preview when ready. Review imported or downloaded HTML before running it.

Test markup and styling

The viewer supports inline HTML and CSS plus limited JavaScript execution inside an isolated frame. Network requests are blocked by a Content Security Policy in the preview; downloaded files may behave differently outside this sandbox.

Frequently asked questions

Does this publish my HTML?

No. Preview and download occur in your browser; this tool does not host websites.

Does the preview load external scripts or images?

No. The preview applies a restrictive network policy and isolates the frame.