Email Subject Line Tester
Score your email subject line, detect spam words, preview inbox appearance, and A/B compare variants.
How the Subject Line Tester Works
Enter your email subject line and get an instant score out of 100 based on length, word count, spam triggers, personalization, and best practices. All analysis runs in your browser.
Scoring Criteria
- Character count — Optimal range is 41-50 characters
- Word count — 6-10 words is the sweet spot for open rates
- Spam trigger words — Penalized for words that trigger spam filters
- Personalization — Using tokens like [name] boosts engagement
- Emoji usage — A single emoji can increase open rates by 56%
- Numbers — Subject lines with numbers tend to perform better
- ALL CAPS — Penalized as it triggers spam filters and reduces trust
- Excessive punctuation — Multiple !!! or ??? are flagged
A/B Comparison
Enter two subject line variants to see scores side by side. The tool highlights which one is stronger and why.
Frequently Asked Questions
The tool analyzes your subject line across multiple factors including character length, word count, spam trigger words, emoji usage, capitalization, and punctuation patterns. Each factor is weighted and combined into an overall score out of 100. Higher scores indicate subject lines that are more likely to achieve good open rates.
Yes. The entire analysis runs 100% client-side in your browser using JavaScript. Your subject lines are never sent to any server, stored in any database, or shared with third parties. You can verify this by checking your browser's network tab.
Spam trigger words are terms like "free," "act now," "limited time," and "guaranteed" that email spam filters commonly flag. Using these words in your subject line increases the chance of your email landing in the spam or promotions folder instead of the primary inbox.
Yes. The A/B comparison feature lets you enter two subject line variants and see their scores, checks, and verdicts side by side. The tool highlights the winner and explains the differences, helping you choose the stronger option before sending your email campaign.
The ideal email subject line is between 30—60 characters (6—10 words). Subject lines under 30 characters may lack context, while those over 60 characters often get truncated on mobile devices. The tool checks your length against these benchmarks and flags subject lines that are too short or too long.