📬 Open Rate Optimizer

Email Subject Line Tester

Type your subject line and instantly get a score, inbox preview, length check, spam detection, power word analysis — everything you need to maximize open rates.

Overall score /100
Mobile inbox preview
Power word detection
Spam word alert
📱 Live Inbox Preview
📱
Mobile
~40 chars
Start typing your subject line...
🖥
Desktop
~60 chars
Start typing your subject line...
Characters: 0 Words: 0 Ideal: 30–50 characters

📏 Subject Line Length Guide

  • 30–50 chars — Sweet spot, works on all devices
  • 51–60 chars — Fine for desktop, cut on mobile
  • 61+ chars — Cut off on most email clients
  • Under 20 chars — Too vague, low open rate
  • Put your most important words first

⚡ Power Words That Boost Opens

  • Curiosity: secret, discover, revealed, inside
  • Urgency: today, now, last chance, expires
  • Exclusivity: exclusive, private, members only
  • Personalization: you, your, [first name]
  • Numbers: "5 ways to...", "3 mistakes..."

Frequently Asked Questions

What is the ideal email subject line length? +
The sweet spot is 30–50 characters. Mobile devices show around 40 characters before cutting off. Most email opens now happen on mobile, so keeping it short ensures the full subject line is visible in the inbox.
What are power words in subject lines? +
Power words are emotionally charged words that trigger curiosity, urgency, or desire. Examples: "secret", "exclusive", "proven", "instantly", "discover", "you", "new", "results". Using 1–2 power words can significantly lift open rates.
Do emojis help email open rates? +
Yes — a single relevant emoji can increase open rates by 25–30% by standing out in the inbox. Avoid using more than 1–2 or they can trigger spam filters in some email clients.
Should I use ALL CAPS in subject lines? +
No. ALL CAPS words are a major spam trigger and look aggressive to recipients. Use title case or sentence case instead for a natural, trustworthy feel.