Email Preview Tool for Developers
If you write HTML emails for a living — whether transactional, marketing, or operational — you need a fast way to test rendering across clients without sending dozens of test emails. MailViewr was built for this workflow, and it's outlined in our ultimate guide to HTML email testing.
What Developers Actually Need
Most email preview tools are designed for marketers. Developers need something different:
- Code editor — Paste raw HTML/CSS and edit directly
- Instant rendering — See changes as you type, not after a 30-second queue
- Client-specific rules — Know exactly which CSS properties fail in which client
- Compatibility scoring — Automated issue detection with line-level references
- Dark mode testing — Toggle dark mode to check color inversions
- No signup for core features — Just paste and preview
How MailViewr Works for Developers
- Paste your HTML — Full code editor with syntax highlighting
- Select clients — Gmail (5 variants), Outlook (3 variants), Apple Mail
- Preview instantly — Rendering updates in real time as you edit
- Check compatibility — Automated scanner shows issues per client with severity levels
- Toggle dark mode — See how dark mode affects your email
- Send test email — Deliver to your real inbox to verify (free account required)
Email Clients Supported
Gmail Variants
- Gmail on Chrome
- Gmail on Firefox
- Gmail on Safari
- Gmail on iOS
- Gmail on Android
Outlook & Others
- Outlook Desktop (Word engine)
- Outlook iOS
- Outlook Android
- Apple Mail
What Tool Can Test HTML Email Across Mobile and Desktop Clients?
MailViewr tests your HTML email across mobile and desktop clients in the browser. Unlike services that take screenshots on remote servers (which can take minutes), MailViewr applies real email client rendering rules locally for instant results.
The compatibility checker runs 100+ rules against your HTML/CSS to flag issues before you send. Issues are categorized by client and severity, with specific fix suggestions for each. For detailed testing strategies, also see our guides on previewing in Gmail and testing Outlook rendering.
Free vs Paid Email Testing Tools
Litmus and Email on Acid offer screenshot-based testing across 80+ clients, but start at $79–$99/month. MailViewr covers the most impactful clients (Gmail and Outlook handle 70%+ of all email opens) and is completely free.
When to use MailViewr: Day-to-day development and testing. Quick checks while building. Pre-send verification for the major clients.
When to use paid tools: Final QA when you need pixel-perfect screenshots across 80+ niche clients.
Start Testing Your Email
Free Developer Tool
Paste your HTML, preview across all major clients, check compatibility, and send test emails — free, no signup needed to preview.
Open Email Tester →