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.
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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.
Why It Matters
Your subject line is a double gate — it determines both deliverability and open rates. A subject line that triggers spam filters never reaches the inbox. One that reaches the inbox but feels generic never gets opened. Cold email subject lines are scrutinized even more heavily because recipients don't recognize the sender. Getting the subject line right is the highest-leverage 5 seconds you spend on any email.
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.
Common Mistakes to Avoid
Writing clickbait subject lines
Deceptive subjects like 'Re: our conversation' or 'Quick question' work once but destroy trust and increase spam complaints. Be specific and honest about what's inside.
Using all caps or excessive punctuation
Subject lines in ALL CAPS or with multiple exclamation marks are among the strongest spam triggers. They also look unprofessional to recipients who do see them.
Making subject lines too long
Anything over 60 characters gets truncated on mobile, which is where most email is read. Front-load the important words so your key message is visible even when cut off.
Not using personalization tokens
Generic subject lines signal bulk email. Adding {{firstName}} or {{company}} tells spam filters (and recipients) that this is a targeted, individual message.
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.
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