Email Subject Line Tester
Type a subject line to see its length rating, spam score, inbox previews with your sender name, and three quick A/B variations.
No spam triggers detected.
No personalization tags. Add {{name}} or [name] for better open rates.
Runs in your browser. Nothing you enter is uploaded.
What it does
A subject line is judged in a split second, next to your sender name and a line of preview text. This tester recreates that view: it shows a Gmail-style desktop row and a narrow mobile row that cuts the subject at 35 characters, using the sender name and snippet you type in.
Alongside the previews it scores common spam signals (FREE, LIMITED TIME, stacked exclamation marks, all-caps words, "click here"), notes whether you used a {{name}} or [name] merge tag, and suggests three variations to test.
How to use it
- 1
Type your subject into "Email subject line" and read the length rating below it.
- 2
Replace "Your Brand" in "From name (preview)" with your sender name.
- 3
Enter your preheader in "Snippet preview text".
- 4
Compare the "Gmail desktop preview" and "Mobile truncated preview".
- 5
Review the spam score and personalization panels, then copy an A/B variation or use "Copy subject".
What you get
A live report: character count with an optimal, below or above rating for 35 to 50 characters, two inbox previews, a spam score out of 100 with the triggers found, a personalization check, and three copyable variations (Free to Bonus, emoji, and shortened).
When to use it
- Pre-send newsletter check
- Paste the week's subject, add your real sender name and preheader, and confirm the key words land before the mobile cut-off.
- Toning down a promo subject
- Watch the spam score drop as you remove capitals and extra exclamation marks from a sale announcement.
- Quick A/B test ideas
- Copy the emoji and shortened variations to set up a subject line test in your email platform.
Example
Input
Your FREE guide to spring planting!!
Output
36 characters · Optimal (35 to 50) Mobile preview: "Your FREE guide to spring planting…" Spam score: 50/100 (Contains "FREE", Multiple exclamation marks, ALL CAPS words, Excessive punctuation) Variations: "Your Bonus guide to spring planting!!" · "✨ Your FREE guide to spring planting!!" · "Your FREE guide to spring"
Rewriting it as "Your spring planting guide is ready" (35 characters) clears every trigger and still fits the range.
Tips
- The score is a checklist of common triggers, not a deliverability test. Sender reputation and authentication (SPF, DKIM, DMARC) matter far more to inbox placement.
- Put the most important words in the first 35 characters, since that is where the mobile preview cuts off.
- Write the snippet as a second line of the pitch. Leaving it empty lets clients fill it with "View in browser" or other boilerplate.
- Only use {{name}} or [name] if your email platform supports that exact merge tag, or recipients will see the raw brackets.
Questions
Does using the word "free" in a subject line send email to spam?
Not by itself. Modern filters weigh many signals, and one word rarely decides placement. The tester flags it because it often appears alongside other spammy patterns, so treat it as a prompt to review, not a verdict.
Why does the tester aim for 35 to 50 characters?
Longer subjects get cut on phones and in narrow inbox panes, and very short ones can lack context. 35 to 50 is a practical middle ground, but a clear 60-character subject can still outperform a vague 40-character one.
Is the mobile preview exactly what my subscribers will see?
It is an approximation. Every mail app and screen size truncates differently, so the 35-character cut is a conservative guide. Send a test to your own phone for the final check.
Does it send a test email or connect to my email platform?
No. The subject, sender name and snippet you type stay in the page for the previews. Use your email platform's test send for a real inbox check.