Paste AI-generated HTML into the free HTML tester before you upload it. It renders the page live, at desktop, tablet, and phone widths, next to a code editor, so you see what a visitor would see before it's live.
Why a pasted single file breaks
ChatGPT, Claude, and Gemini often answer with one HTML block, not a project folder. Copy that block straight into a site and the browser tries to load everything it references: a stylesheet, a script, an image. If those files never existed outside the chat window, the page you uploaded is not the page you saw.
The same gap shows up as a blank page, unstyled markup, or a button that does nothing. All three trace back to a reference the uploaded files can't satisfy.
What you see before you upload
The HTML tester renders exactly what you pasted, live, at desktop, tablet, and phone widths, with a code editor next to it so you can fix something and watch it re-render without leaving the tab. It doesn't scan your markup for you: a missing stylesheet shows up as unstyled text, a missing script shows up as a button that does nothing, and a missing image shows up as a broken-image icon. You're looking at the same page a visitor would get, before anyone else does.
<html>
<head>
<link rel="stylesheet" href="style.css" />
</head>
<body>
<h1>My AI-generated page</h1>
<script src="script.js"></script>
</body>
</html>
Paste that into the tester and you'll see it yourself: no styling applied, and nothing happens if there were a button wired to that script. Nobody points it out for you, but it's obvious once you're looking at the live page instead of the chat window, and you're looking at it before either missing file has a chance to go live at a real URL.
A two-minute check before you upload
Paste the file, watch it render, fix what's missing, then upload. If the assistant only gave you markup, either ask it for the stylesheet and script it referenced or strip the reference and inline the rule directly in the HTML. Either way, you see it in the tester, not from a visitor.
