Email CSS compatibility checker
Not every client supports the CSS you write. Paste your email HTML to get a per-client compatibility score across Gmail, Outlook, Apple Mail and 12 more, plus copy-paste fixes for the properties that break.
Frequently asked questions
Which email clients does this check against?
Twenty-one: Gmail (web, Android, iOS), Outlook 365, Outlook (New), Outlook Classic, Outlook mobile (iOS, Android), Outlook for Mac, Apple Mail (macOS and iOS), Yahoo Mail (web, Android, iOS), Samsung Mail, Thunderbird, HEY, Proton Mail, AOL, Fastmail and Superhuman. Each has its own CSS support profile, so a property that's fine in Apple Mail can be dropped entirely by Outlook.
How is the compatibility score calculated?
Every CSS property in your email is checked against each client's known support. Unsupported properties that break layout count as errors; partially-supported or cosmetic ones count as warnings. The per-client score reflects how much of your CSS that client will honor; the headline number is the average across all 15.
Why does Outlook score lower than everything else?
Outlook on Windows renders with Microsoft Word's engine, which ignores modern CSS like flexbox, grid, border-radius and background gradients. That's why table-based layouts and VML fallbacks still matter. This checker flags exactly which properties Outlook will drop and suggests what to use instead.
What's the difference between this and inlining CSS?
Inlining moves your CSS to where clients can read it; compatibility checking tells you whether they support it at all. They're complementary steps. Inline first with the CSS inliner, then check what each client actually honors here.