About HTML Email Preview & Responsiveness Sandbox
Professional email rendering sandbox and deliverability auditor. Inspect HTML marketing templates across Desktop, Tablet, and Mobile viewports, simulate client dark mode inversions, test layout resilience with image blocking, and audit code against 600px container constraints and missing alt tags.
Key Capabilities & Features
- Multi-device viewport toggles: Desktop (600px), Tablet (480px), Mobile (375px)
- Simulated Dark Mode to preview color inversion and contrast issues
- Image Blocking test to verify email legibility when recipient clients disable remote images
- Automated 600px container width auditor and missing image alt tag detector
- Spam trigger word detection and deliverability health score
How to Use HTML Email Preview & Responsiveness Sandbox
Paste HTML Code
Paste your HTML newsletter template into the code editor or load our starter template.
Switch Viewports
Test how the layout renders on desktop, tablet, and mobile screens.
Run Compatibility Audit
Check the health panel for 600px constraints, missing alt attributes, and spam words.
Privacy & In-Browser Execution Guarantee
100% in-browser rendering using a sandboxed iframe. Your HTML templates never touch external servers.
Frequently Asked Questions
Why is 600px the industry standard width for HTML emails?
Most desktop webmail clients (like Outlook, Yahoo, and Gmail) render emails within a 3-column pane, leaving approximately 600px of visible horizontal width without requiring horizontal scrolling.
Why test with image blocking enabled?
Many email clients block remote images by default for privacy reasons. Accessible emails must remain informative and readable even when images fail to render.