Free Tool
Subject Line Tester
Predict your open rate before you hit send. Scored against 5M+ cold email benchmarks from 2026.
Your Subject Line
Predicted Open Rate
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Signals
Predicted Open Rate
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Signals
Testing History
Your tested subject lines will appear here. Stored locally — never sent to any server.
Frequently Asked Questions
How accurate is the predicted open rate?
Predictions are based on 2026 aggregate benchmarks from 5M+ analyzed emails (Snov.io, Instantly.ai, Lavender Labs). They reflect statistical patterns — your actual open rate depends on sender reputation, list quality, deliverability, and timing. Use the prediction as a relative guide: a subject line scoring 48% will likely outperform one scoring 35%.
What makes a good cold email subject line?
Based on 2026 data: 21-40 characters (49.1% open rate), trigger event references (+42.4% lift), numbers in the subject (+45% lift), and lowercase or sentence case (ALL CAPS gets -8.9%). The single biggest lever is relevance — a subject referencing a specific trigger event outperforms generic personalization by 4x.
What's the ideal subject line length?
21-40 characters is the sweet spot (49.1% open rate). In terms of word count, 3, 7, or 8 words perform best. Shorter subjects work because they're fully visible in mobile inbox previews and feel conversational rather than promotional.
Does putting the recipient's first name in the subject line help?
Barely. First name personalization lifts open rates by only 9.6% vs. baseline. Compare that to trigger event references (+42.4%), industry/role references (+25.8%), or company name (+21.9%). First name tokens also look templated to savvy recipients and some spam filters. Use a trigger event or company reference instead.
Good Subject Lines Open Doors. Earned Authority Keeps Them Open.
The best subject line in the world still caps at 5% reply rate if they don't know who you are.