How to Test and Preview HTML Email Templates
Use the HTML Email Tester to preview your email template, catch compatibility issues, and ensure it renders correctly across email clients.
Tool Used
HTML Email Tester
Paste your HTML email template
Open the HTML Email Tester tool. Paste your HTML email markup into the input panel. The template should include all inline styles — most email clients strip external stylesheets and <style> blocks. If your template uses a separate CSS file, you need to inline the styles first using a CSS inliner before pasting.
View the rendered preview
The preview panel renders your template as it would appear in an email client. Check that fonts, colors, spacing, and images look as intended. Toggle between desktop preview (600px width) and mobile preview (375px width) to check both viewports. An email that looks good at 600px may break at mobile width if the layout uses fixed pixel widths instead of percentage widths.
Review compatibility warnings
The tool flags HTML and CSS that is not supported in common email clients. Common warnings: CSS Flexbox (not supported in Outlook), CSS Grid (not supported in Outlook), background-image shorthand (limited support), CSS variables (not supported in most clients), and external fonts via @font-face (limited support). For each warning, the tool suggests a compatible alternative.
Check for common issues
The tool also checks for: images missing alt text (important when images are blocked), images without explicit width and height attributes (causes layout shifts), links with no href, missing preheader text (the preview text shown in the inbox list), email size exceeding 102KB (Gmail clips large emails), and no plain-text fallback mentioned. Address each issue before sending.
Validate and copy the final template
Once the preview looks correct and no critical warnings remain, click Copy HTML to copy the final template. Paste it into your email sending service (SendGrid, Postmark, Mailchimp, AWS SES). Send a test email to yourself and check it in at least Gmail, Apple Mail, and Outlook if possible — even with the tester, testing in real clients is the only way to be certain.
All done!
You are ready to use HTML Email Tester like a pro.