Subject Line Analyzer
Score email subject lines for deliverability and engagement.
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Use tool →How to Write Better Email Subject Lines
Type your subject line above and hit Analyze. The tool scores it across seven categories: length, power words, spam risk, personalization, readability, formatting, and engagement signals. Each category contributes to a score out of 100. You get a breakdown showing exactly where you're strong and where you can improve.
The mobile preview shows how your subject line will look on a phone inbox. Most people check email on mobile first, so if your subject line gets cut off at 40 characters, your best selling point might never be seen. Front-load the important words.
What Makes a Good Subject Line?
The best subject lines are specific, concise, and give the reader a reason to open. Vague subjects like "Newsletter #47" or "Quick update" don't tell anyone why they should care. A subject line that says "Your trial expires Friday" or "3 mistakes killing your conversion rate" gives a clear reason to click.
Numbers, questions, and personalization tokens all correlate with higher open rates. But the biggest factor is relevance. No amount of power words will save a subject line that doesn't match what the reader signed up for. Write for your audience, not for a scoring tool.
About Spam Trigger Words
Modern spam filters use machine learning, not simple word lists. A single "free" in your subject line won't tank your deliverability. But stacking multiple trigger words — "FREE!!! ACT NOW!!! GUARANTEED WINNER!!!" — will. This tool flags patterns that increase spam filter risk, not words that will automatically block your email. Context matters more than individual words.