Email Subject Line Tester

Score your cold email subject lines before you send. Our analyzer checks length, spam triggers, personalization, power words, and mobile preview — then gives you a letter grade with actionable tips to improve deliverability and reply rates.

What We Analyze

• Length Optimization — Optimal subject lines are 17-40 characters. We check mobile preview (35 chars) and desktop preview (60 chars) cutoffs.
• Spam Trigger Detection — Scans for 45+ subject-line-specific spam triggers that get your email filtered before it's ever seen.
• Overused Pattern Detection — Flags 22+ cliché cold email patterns like "quick question," fake Re:/Fw: prefixes, and "touching base."
• Power Words — Detects 30+ proven words that drive engagement: you, noticed, growing, idea, question, and more.
• Personalization Check — Looks for merge tags ({{firstName}}, {company}, etc.) that make your email feel 1-to-1, not mass blasted.
• Formatting Analysis — Flags ALL CAPS, excessive punctuation, emoji overuse, and title case that hurt deliverability.

Cold Email Subject Line Best Practices

• Keep subject lines under 40 characters for best mobile display
• Use lowercase — title case feels like marketing, not a real person
• Include the recipient's name or company — makes it feel personal, not templated
• Ask a question to drive curiosity and engagement
• Include a number for specificity (e.g., "3 ideas for {{company}}")
• Avoid fake Re: or Fw: prefixes — they destroy trust immediately
• Never use ALL CAPS or multiple exclamation marks
• Test multiple variations — small changes can mean 2-3x differences in reply rates