This viewer shows your HTML in an isolated frame. Scripts do not run and forms cannot submit, so you can look at markup from a source you do not fully trust without it doing anything.
It is handy for checking an email template, a snippet from a CMS or the output of one of the converters on this site.
Frequently asked questions
Why do my scripts not run?
The preview frame is sandboxed on purpose. That keeps unknown HTML from running code. To test JavaScript, use your own browser or a dev environment.
Do external images and stylesheets load?
Images and stylesheets from other sites may load, depending on your browser. Relative links will not work because there is no base address.
Can I use it to preview an email?
Yes for a rough look. Email clients render HTML differently, so test the final message in the clients you care about.