The email subject analyzer scores your subject line across 7 deliverability and engagement dimensions — detecting spam triggers, measuring length fit, urgency level, and personalization — to predict whether your email will land in the inbox or the spam folder.
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Compare up to 3 subject lines
How to Write Email Subject Lines That Actually Get Opened
The average office worker receives 121 emails per day. Your subject line has less than 2 seconds to earn an open — and it's competing against every other sender in the inbox. Understanding what makes a high-performing subject line isn't just useful; it's the difference between a 12% open rate and a 28% open rate.
How We Score Email Subject Lines
This tool evaluates 7 dimensions that research has shown to impact open rates:
- Length — Mobile sweet spot is 30-50 characters; desktop performs better at 40-60. Very long subjects get truncated.
- Spam Risk — Spam filters flag ALL CAPS words, excessive punctuation (!!!), and trigger phrases like "free", "act now", "guaranteed".
- Personalization — Merge tags ([First Name]) and "you/your" language increase relevance signals.
- Urgency — Moderate urgency ("today", "deadline") boosts opens. Excessive urgency ("ACT NOW!!!") reads as spam.
- Emotional Impact — Power words like "exclusive", "breaking", "secret" trigger curiosity and urgency.
- Preview Text Compatibility — The first 40 characters should communicate value independently for mobile preview panes.
- A/B Testability — Does the subject contain a specific, testable element (a number, an adjective, a question format)?
Step 1: Pick the Right Length for Your Platform
For promotional emails going to mobile-heavy lists, keep subject lines under 45 characters. Gmail on mobile shows approximately 30-35 characters in portrait mode. If your subject line carries all the value in the second half, most subscribers will never see it. Test both a short and long version using the comparison mode.
Step 2: Avoid Spam Traps
Modern spam filters use context, not just word lists — but subject lines still trigger filters more often than any other email element. The safest approach: write naturally, avoid all-caps emphasis, use exclamation points sparingly (one maximum), and never combine multiple risk factors (free + act now + !!!). A spam score of 3+ in this tool indicates serious deliverability risk.
Step 3: Use the Comparison Mode for A/B Testing
Always write at least 2-3 variations before sending. Compare a question format vs. a statement format. Test with vs. without a number. Try personalized vs. non-personalized. The comparison mode scores each variant objectively and identifies the statistically stronger option based on best-practice signals.
FAQ
Is this email subject analyzer free?
Yes, completely free with no signup required. All analysis runs locally in your browser — your subject lines are never sent to any server or stored anywhere.
How is the open rate prediction calculated?
The predicted open rate category (above average, average, below average) is based on scoring 7 factors: length optimization, spam risk, personalization, urgency level, emotional impact, preview text compatibility, and A/B testability. A score of 85+ predicts above average open rates; 60-84 is average; below 60 suggests below average performance.
What spam trigger words hurt email deliverability?
Common spam triggers include: 'free', 'act now', 'limited time', 'click here', 'guaranteed', 'winner', 'earn money', 'cash bonus', and excessive punctuation like '!!!' or '???'. ALL CAPS words also raise spam scores significantly. This tool checks for 30+ known spam trigger patterns.
What is the ideal email subject line length?
For mobile inboxes, 30-50 characters is ideal since most phones show only the first 40 characters in portrait mode. Desktop clients display 60+ characters. Aim for 6-9 words that communicate the core value without getting cut off. Very short subjects (under 20 chars) can feel cryptic; very long ones get truncated.
How does personalization affect email open rates?
Personalized subject lines using merge tags like [First Name] or 'you/your' language typically see 10-26% higher open rates. However, generic or overused personalization (e.g., 'Hey [FNAME]') can backfire if it feels robotic. Natural personalization tied to context works best.
How do I use the comparison mode for A/B testing?
Click 'Compare Subjects' to add up to 3 subject lines side-by-side. Each line gets scored individually, and the highest-scoring subject line receives a 'Winner' badge. Use this to A/B test variations: try a question vs. a statement, with vs. without numbers, or different urgency levels.