Donaldson R F HTML Email Previewer & Editor
Paste or write HTML email code, see it rendered instantly at desktop and phone widths, simulate blocked images, and get warnings about things email programs do not support.
What this preview can and cannot tell you
The preview renders your HTML in a sealed frame: scripts never run, forms do not work and, if you choose Block images, remote images are not loaded — which is how many email programs behave until the reader allows images. The dark mode is a rough inversion to show how a message can look when a program darkens it automatically; real programs differ. Widths are for a quick responsive check.
It uses your browser’s rendering engine, which is far more capable than Outlook for Windows (which uses Word to draw email), Gmail or older apps. The warnings list common causes of trouble — flexbox/grid, scripts, missing alt text, size — but always test in real email programs before sending to a large list. To pick out which CSS works where, keep layouts table-based, use inline styles and a single 600 px column. Check your subject line with the subject line checker.
Frequently asked questions
Does the preview send anything?
No. The HTML stays in your browser and is shown in a sandboxed frame that cannot run scripts.
Why does it look different in Outlook?
Outlook for Windows renders with Microsoft Word, which ignores many modern CSS features; test there separately.
What is the 102 KB warning?
Gmail cuts off (“clips”) messages whose HTML is over roughly 102 KB, hiding the rest behind a link.