HTML Viewer Online

HTML Viewer Cat lets you view any HTML code rendered as a web page. Paste a snippet, a full page, or an email template — and see exactly how a browser interprets it. The viewer updates in real time with syntax highlighting to help you read the source code alongside the rendered output.

What is an HTML viewer?

An HTML viewer takes raw HTML source code and renders it visually — showing you exactly what a user would see in their browser. It's the quickest way to check how HTML markup translates into a visible web page, without creating files or running a development server.

HTML viewer vs. HTML editor

An HTML viewer focuses on displaying rendered output from existing code. An HTML editor lets you write and modify code. HTML Viewer Cat does both — you can paste existing HTML to view it, or write new HTML from scratch. The split-pane layout shows your code and its rendered output side by side.

When to use an online HTML viewer

• Inspecting HTML from emails — view the source of an HTML email to understand its structure or debug rendering issues
• Checking code snippets — paste HTML from a tutorial, documentation, or Stack Overflow to see what it produces
• Reviewing code changes — view HTML output from a diff or pull request to check visual correctness
• Testing across devices — use the responsive preview to see how HTML renders on different screen sizes

How it works

Your HTML is rendered in a sandboxed iframe directly in your browser. Nothing is uploaded to a server — the entire process is client-side. This means it's fast (no network round-trip), private (your code stays local), and works offline once the page is loaded.