Email Subject Line Tester & Scorer
Analyze your subject line against spam filters and deliverability best practices. Get a real-time score with checklist to help you land in the inbox.
Expert Tip: What makes a good subject line?
Keep it between 3-15 words (under 60 characters), use one personalization token like {{first_name}}, and avoid spam-triggering words like 'Free' or 'Act Now' to ensure your email bypasses junk filters.
Enter an email subject line to start the deliverability analysis.
Tip: Personalize
Personalized subject lines increase open rates as much as 26%.
Tip: Mobile First
Keep it under 60 chars to avoid getting cut off on phones.
Tip: Be Honest
Avoid deceptive prefixes like "RE:" or "FWD:" to build trust.
Why Subject Line Analysis Matters
Your subject line determines both deliverability and open rates.
Bypass Spam Filters
Certain words and characters trigger modern email filters. Testing ensures your message reaches the primary inbox.
Optimize for Mobile
Over 50% of emails are read on mobile. We help you front-load your message so it doesn't get cut off.
"Your subject line is the single biggest factor in whether your email gets opened. Test once, send with confidence."
Frequently Asked Questions
Common questions about email deliverability and subject line optimization.
How accurate is the spam word detector?
Our tool checks against a comprehensive, regularly updated list of hundreds of known spam trigger words used by major ESPs like Gmail and Outlook to flag promotional or malicious emails.
What is the ideal length for a subject line?
For optimal rendering on both desktop and mobile devices, we recommend keeping your subject line between 3 and 8 words, or roughly 40-60 characters.
Does capitalization really matter?
Yes. Using ALL CAPS triggers spam filters and often looks unprofessional or 'shouty' to the recipient. Use sentence case or title case instead.
Should I use emojis in my subject line?
Emojis can increase open rates by making your email stand out, but using more than one can look like spam. We recommend a maximum of one relevant emoji per subject line.
Why is my subject line score low even if I don't use spam words?
A good subject line isn't just about avoiding spam words. Our score also penalizes you if the subject is too short, too long, uses excessive punctuation (like multiple exclamation marks), or lacks personalization.
Are my subject lines stored or tracked?
No. All analysis is performed entirely in your browser. We do not transmit, save, or track the subject lines you test using this tool.
Add the Final Touch to Your Emails
A great subject line gets them in, a professional signature builds the trust. Create yours for free today.