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Email Subject Line Tester
Paste a subject line to score it out of 100. You'll see exactly which words help, which look like spam, how it's cut off in a phone inbox, and you can ask AI for 12 stronger rewrites.
43 characters · 7 words
Last chance: your spring order ships FREE!!
power word spam trigger ALL CAPS
Score breakdown
- Length25/25
43 characters: fits a phone inbox without being cut off.
- Word count10/10
7 words: in the 4–9 word sweet spot.
- Spam triggers20/20
No common spam trigger phrases.
- Power words15/15
Uses “last”, “your”.
- Formatting6/15
Tone it down: ALL CAPS: FREE!!; 2 exclamation marks.
- Personal8/8
Speaks directly to the reader.
- Specificity0/7
A number, a question or “how to” makes the payoff concrete.
Inbox preview
Usually fully visible; narrow phones may cut the last few characters.
Rewrite it with AI
12 alternative versions that keep your intent. Each is scored like the one above.
What this subject line tester checks
Most subject line analyzers hand you a number without telling you where it came from. This one shows its working. The score is the sum of seven factors you control in the line itself:
- Length (25 points). Phone inboxes typically show somewhere around 30 to 45 characters of a subject. 28–50 characters scores full points. See how long a subject line should be.
- Spam triggers (20). Phrases long associated with spam, like “act now”, “100%” or “risk-free”. Filters today weigh sender reputation and engagement far more, but these phrases still make people skip. Full list: spam trigger words.
- Power words (15). Words that add curiosity, value, urgency or warmth. See the power words list.
- Formatting (15). ALL CAPS words, more than one exclamation mark, emoji clutter or repeated symbols lose points.
- Word count (10). 4–9 words is the sweet spot for most campaigns.
- Personal (8). “You”, “your” or a merge tag like {first_name}.
- Specificity (7). A number, one question or a “how to” sets a clear expectation.
A score is a guide, not a forecast. Open rates are driven mostly by list quality, sender reputation and timing, and since Apple Mail Privacy Protection they are also inflated by automatic opens (explained on our open rate page). Use the tester to remove weak lines, then A/B test the two best with your own audience.
Frequently asked questions
What is a good subject line score?
On this tester, 85+ is strong, 70–84 good, 50–69 needs work and under 50 weak. Most well-written campaign lines land between 70 and 95. A cold email written in plain lowercase may score a little lower on power words and still perform well.
Can a subject line tester predict my open rate?
No tool can do that reliably from the text alone. Open rates depend on your audience, sender reputation, inbox placement and timing, and are inflated by Apple Mail Privacy Protection. A tester catches avoidable problems; an A/B test with your list tells you what works.
Do spam words really send email to spam?
Rarely on their own. Gmail, Outlook and Yahoo rely mainly on authentication (SPF, DKIM, DMARC), sender reputation and how recipients engage. But hype-heavy wording lowers engagement, which does affect reputation over time.
What is preview text (preheader)?
The snippet shown after or below the subject line in most inboxes. If you do not set it, the inbox pulls the first text in your email, often “View in browser”. Treat it as a second subject line that adds detail.
Is my subject line stored?
Scoring runs entirely in your browser. Only if you click “Get 12 rewrites” is the line sent to an AI model to write alternatives; we do not store it.