The code editor now warns when pasted HTML looks incompatible with email clients.
In a world of mostly-compatible web standards, developers often assume that email clients support many modern features as well.
Today, we're introducing an email compatibility checker in the code editor for Templates and Broadcasts to help you catch major compatibility issues beforehand so you can send with confidence.
As you edit HTML in the editor, your emails are scanned for patterns that clients strip or render inconsistently.
When you upload an HTML email template using the editor (via the CLI, MCP, API, etc.), the checker runs automatically.
The editor marks flagged code with a wavy underline colored by severity and a warning badge shows a full overview of the issues found.
You can also use the compatibility checker in HTML code blocks within the visual editor.
Client support data comes from caniemail and is refreshed daily so it reflects the latest email client support. It catches major known issues like:
<script> tags, event handler attributes like onclick, <iframe>, linked stylesheets, <svg>, forms, and more.display: flex and grid in Outlook for Windows, position: fixed, viewport units, and CSS math functions like clamp().oklch() and color-mix().data-reactroot or Next.js/Nuxt root IDs, a sign the HTML wasn't written for email in the first place.As always, you can send yourself a test Broadcast or Template to see how your email looks in your own email client.
We're happy to bring this new compatibility checker to code blocks within the Resend editors, giving you more confidence when sending. If you have any questions, please reach out to us and we'll be happy to help.