AI Email Subject Line Tester
Test your email subject line with AI. Get a score, spam risk analysis, and 5 improved alternatives — all instantly.
Quick Answer
The ideal email subject line is 30-50 characters long, as this range achieves the highest open rates across devices. Subject lines with ALL CAPS, excessive exclamation marks, or spam trigger words like “free,” “act now,” and “guaranteed” significantly increase the chance of landing in spam folders. Including numbers and personalization tokens can boost open rates by 10-20%.
About This Tool
The AI Email Subject Line Tester analyzes your email subject lines using artificial intelligence to predict performance before you hit send. It evaluates length, emotional impact, personalization opportunities, urgency triggers, curiosity gaps, and spam risk — the key factors that determine whether your email gets opened or ignored.
Email subject lines are the single most important factor in open rates. Research consistently shows that 47% of email recipients decide whether to open an email based on the subject line alone, and 69% report emails as spam based solely on the subject line. A well-crafted subject line can mean the difference between a 15% and 40% open rate.
The tool also generates five alternative subject lines tailored to your content and email type. Each alternative is designed to improve on a different aspect of your original — one might boost urgency, another might add personalization, and another might create a stronger curiosity gap. You can click “Use this” to instantly copy any alternative.
For best results, select your email type (newsletter, promotional, transactional, or cold outreach) so the AI can calibrate its analysis. A subject line that works well for a newsletter may score differently for cold outreach, where different psychological triggers apply.