Email Subject Line Tester
Score email subject lines to maximize open rates. Detects spam keywords, tests character limits, and previews mobile inbox truncation in real-time.
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Step-by-Step Instructions
Enter Email Subject Line
Type or paste your proposed email marketing subject line.
Add Preview Preheader Text (Optional)
Input preview preheader text to evaluate combined inbox presentation.
Analyze Spam Score & Character Limits
Review character count (target 30–50 chars), mobile pixel width (max 400px), and spam trigger word detection.
Review Multi-Device Previews
Examine live simulated previews for iPhone Mail, Gmail Mobile, Outlook Desktop, and Apple Mail.
Key Features & Capabilities
- Spam trigger word detection algorithm identifying aggressive promotional flags (FREE, Guarantee, Urgent, $$$)
- Mobile screen cutoff predictor calculating character limits and pixel width constraints across iPhone and Android clients
- Urgency, curiosity, and emotional sentiment scoring framework
- Preview text / preheader optimization analyzer maximizing open rates (OR)
Frequently Asked Questions
What is the ideal length for an email subject line on mobile devices?
Most smartphone email apps (Apple Mail, Gmail for iOS/Android) display between **30 and 45 characters (approx. 400 pixels width)** before cutting off text. Keeping subject lines under 40 characters ensures the full hook is visible without truncation.
What words trigger email spam filters?
Spam filters (SpamAssassin, Barracuda) penalize words associated with aggressive sales tactics: excessive capitalization ('URGENT', 'FREE'), currency symbols ('$$$'), trigger words ('100% Free', 'Guaranteed', 'No Risk', 'Risk-Free', 'Act Now', 'Miracle'), and deceptive prefixes ('Re:', 'Fwd:' when not a reply).
How does preheader preview text complement the subject line?
Preheader text is the snippet of text pulled from the first line of the email body and displayed next to or below the subject line in the inbox. Pairing a short subject line with an engaging 40–90 character preheader provides dual hooks that significantly increase email open rates.
Do emojis in subject lines increase open rates?
A single, contextually relevant emoji can increase open rates by 10%–15% by standing out visually in a crowded inbox. However, using multiple emojis or deceptive icons (like fake notification badges 🔴) triggers spam flags and degrades deliverability.
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