Email client compatibility
Checks your HTML against rendering rules for Outlook, Gmail, Apple Mail, Yahoo, and mobile clients. Catches unsupported CSS, broken layouts, missing fallbacks.
Free tool · Powered by Claude
An AI code review for your email HTML.
Paste your HTML and get an instant review. Catches Outlook quirks, accessibility issues, dark-mode gaps, and 50+ best-practice rules before you hit send.
How it works
Three steps to better email HTML
No account needed for your first review.
- 01
Paste your code
Copy your email's HTML source and paste it in. Up to 500 KB from any source: hand-coded, builder-exported, or ESP-generated.
- 02
Get an instant review
The AI analyses your code against 50+ rules covering compatibility, accessibility, dark mode, performance, and best practices. Results are categorised by severity.
- 03
Fix issues before you send
Each issue includes the affected clients, an explanation, and a specific fix recommendation with code. Address critical first, then warnings.
What it checks
Comprehensive email code analysis
Every aspect of email HTML quality, from rendering compatibility across 20+ clients to accessibility and deliverability.
Accessibility
Reviews alt text, contrast, semantic structure, and ARIA usage. Ensures readability when images are blocked and accessibility for screen-reader users.
Dark mode readiness
Detects missing dark mode support: prefers-color-scheme media queries, color-scheme meta tags, images that look bad on dark backgrounds.
Performance
Flags emails at risk of Gmail clipping (over 102 KB), excessive image-to-text ratios that trigger spam filters, and bloat from unused styles.
Best practices
Validates inline styles, responsive patterns, bulletproof buttons, table-for-layout usage, DOCTYPE, and Outlook conditional comments.
FAQ
The tool, in detail
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Is this tool really free?
Yes. The first review is free with no account required. Register to unlock 5 reviews per day. No credit card, no hidden fees. -
What email clients does it check for?
All major clients: Outlook (Windows, Mac, web), Gmail (desktop and mobile), Apple Mail, iOS Mail, Yahoo Mail, Samsung Mail. It also checks for issues specific to Outlook's Word rendering engine and Gmail's CSS stripping. -
How is this different from Litmus or Email on Acid?
This tool is a code review, not a visual rendering test. It analyses HTML and flags compatibility, accessibility, and best-practice issues. Think of it as a linter for email HTML. Run it before the visual testing stage. -
Is my email code stored?
No. Your HTML is sent to the AI for analysis and is not stored on our servers. The code is processed in memory and discarded after the review. -
What AI model powers this?
The reviews are powered by Claude, an AI model built by Anthropic, given a specialised system prompt with deep knowledge of email client rendering engines and best practices. -
Can I review any HTML email?
Yes. Paste any HTML email: hand-coded, exported from a builder, generated by an ESP. The tool accepts up to 500 KB of HTML; over that and you should optimise first since Gmail clips above 102 KB anyway. -
What types of issues does it catch?
Critical rendering issues (flexbox or CSS grid in layouts), accessibility problems (missing alt text, poor contrast), dark-mode compatibility, performance concerns (file size, Gmail clipping risk), and general best practices (inline styles, bulletproof buttons, Outlook conditional comments). -
Do I need to know HTML?
You need access to your email's HTML source. Most email builders or ESPs let you export or copy the HTML. Paste it in and you'll get a plain-language review with specific fix recommendations. For a tool where non-technical teams manage email content without ever touching HTML, see Modular Mail. -
How accurate are the reviews?
The AI follows strict rules about what's valid in email HTML; it won't incorrectly flag table-based layouts or inline styles as problems. Always test your final email visually in your target clients before sending.