Email Subject Line Tester & Grader
Test, score, and optimise your email subject lines with spam word detection, mobile preview simulators, and open-rate improvement suggestions.
Inbox Display Previews
Analysis & Recommendations
✓ What Works Well
- Length is optimal for mobile email clients (30–60 chars).
- Contains specific numbers, which boost curiosity and click-through rates.
- Zero high-risk spam words detected.
⚠ Suggestions to Improve
- Consider adding recipient personalization (e.g. {{firstName}} or [Name]).
- Test adding a relevant emoji to increase inbox visual prominence.
About this tool
How to use it
- Type or paste your proposed email subject line into the main input field, or pick a sample preset (Curiosity, Urgency, B2B, or Spam Warning).
- Optionally enter companion preheader (preview) text and your sender name to evaluate the full inbox pitch.
- Review your 0–100 score, letter grade (A+ through F), character count, word count, and spam trigger risk indicators.
- Check the realistic iPhone Mail, Gmail Mobile, and Desktop Webmail mockup previews to verify text doesn't truncate prematurely.
- Follow the actionable recommendations under 'What Works Well' and 'Suggestions to Improve' to optimize deliverability and open rates, then click 'Copy Subject'.
Why it matters
["Protects inbox deliverability: Flags over 50 known spam trigger phrases (such as '100% free', 'guaranteed', 'risk-free', and 'earn cash') that cause email filters to route messages to junk folders.", 'Prevents mobile truncation: Over 60% of all emails are opened on mobile devices where subject lines are clipped after 35–45 characters. Visual previews guarantee your hook is visible.', 'Maximizes open rates: Evaluates cognitive drivers of opens, including curiosity hooks, numerals, dynamic personalization tags, and optimal word length (4–8 words).', '100% privacy-preserving: Runs entirely inside your browser with zero server transmission, ensuring confidential marketing campaigns and internal communications remain private.']
When to use it
['Email newsletter creation: Testing subject line variants before scheduling your weekly or monthly newsletter broadcast.', 'Cold outreach & B2B sales: Crafting high-converting outbound sales sequences that bypass aggressive spam filters.', 'E-commerce promotions: Optimizing flash sale announcements, cart abandonment recovery emails, and discount codes.', 'Transactional emails: Writing clear, authoritative subject lines for order confirmations, onboarding steps, and account notices.']
Common questions
What is the optimal character length for an email subject line?
Between 30 and 55 characters (roughly 4 to 8 words). This fits comfortably across both iOS Mail and Android Gmail apps without getting truncated.
Should I use emojis in my subject lines?
A single relevant emoji can help your email stand out in crowded inboxes and lift open rates. However, using 3 or more emojis triggers spam filters and diminishes trust.
What is preheader text and why is it important?
Preheader text is the preview snippet displayed next to or below the subject line in email clients. A well-crafted preheader acts as a secondary hook that complements your subject line.
Does this tool send my subject lines or email lists to any server?
No. The entire scoring algorithm, spam filter dictionary, and inbox layout simulators run 100% locally in your browser.