About the HTML Viewer and Live Preview
The viewer renders your HTML in an isolated frame inside the page. Inline styles and <style> blocks apply, so you can preview a layout, an email template or a documentation snippet exactly as a browser would show it. The preview updates 300 milliseconds after you stop typing, which makes it a quick scratchpad for trying a CSS rule or checking how a table wraps.
The frame is sandboxed: rendered HTML cannot reach the rest of this page, cannot navigate the browser, and has no access to cookies or storage. Scripts do not run in the preview, which keeps pasted markup from untrusted sources harmless; use the JavaScript Runner to execute code. External images and stylesheets referenced by absolute URL will load if the browser allows them, so the preview of a real page is often close to complete.
Common uses are checking a snippet before pasting it into a CMS, previewing an HTML email, testing an embed code, or reading a saved page without opening it in a tab. The Download button saves the source as an .html file. To format the source, send it to the HTML Formatter.
How to use
- Paste HTML on the left, or click Sample for a small page.
- Watch the rendered result on the right update as you edit.
- Download the source as a file when you are done.
Common questions
- Why do my scripts not run in the preview?
- Scripts are disabled in the preview frame so that pasted HTML can never affect this page or your browser. The JavaScript Runner executes code in a separate sandbox.
- Can I preview a full page with external CSS?
- Yes, if the stylesheet is referenced by an absolute https URL and the host allows it to be loaded. Relative URLs will not resolve.
- Is anything uploaded?
- No. The HTML is rendered locally in a frame on this page.
- Does it show a mobile view?
- Use the fullscreen button and resize your browser, or drag the page narrower; the frame follows the pane width.