Email Subject Line Tester
Analyze your subject line against deliverability best practices. Get a Deliverability Score based on spam triggers, formatting issues, personalization, and length — with a pass/fail checklist for every check.
0 words
0/60 characters
What is Email Subject Line Tester?
Your email subject line is the single biggest factor in whether your email gets opened. But a great subject line that triggers spam filters never gets seen. This tool scores your subject line for deliverability — will it reach the inbox? It checks for spam trigger words, ALL CAPS, deceptive patterns, optimal length, personalization tokens, URLs, and currency symbols.
How to Use This Tool
Type Your Subject Line
Enter your email subject line in the text box above. Analysis runs instantly as you type — no need to click anything.
Check Your Score
You'll see a Deliverability Score from 0 to 100. Green (80+) means good, yellow (50-79) needs work, red (<50) needs significant changes.
Follow the Checklist
Review each check item below your score. Fix any red or yellow items for the best results. Iterate until your score is green.
Warm Up Before Sending
A great subject line needs a warmed-up sender reputation to reach the inbox. Use TrulyInbox to build your reputation before launching campaigns.
Frequently Asked Questions
A good subject line is 3-15 words (under 60 characters), avoids spam trigger words, includes personalization (like {{firstName}}), and doesn't use ALL CAPS or excessive punctuation. It should be specific, honest, and relevant to the recipient.
Under 60 characters is ideal — it won't be truncated in most email clients. Gmail cuts off around 70 characters on desktop and even shorter on mobile. Keep it concise and front-load the important words.
Email service providers use personalization tokens (like {{firstName}}) as a signal that you're sending targeted, individual emails — not bulk spam. Personalized subject lines improve inbox placement rates and reduce the chance of being filtered.
One emoji can help your subject line stand out in a crowded inbox. But more than one can trigger spam filters and look unprofessional. If you use emoji, make sure the subject line works without it too.
No. This tool runs entirely in your browser. Your subject line never leaves your device — it's not sent to any server or stored anywhere.