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Email Subject Line Tester
ContentScore subject lines, preview mobile fit, and create test variants.
ttb run email-subject-line-tester
Test a subject line
44 characters94/100
Inbox preview
from you@example.com
Quick idea to improve your onboarding emails
Preview text would sit here under the subject line.
Strengths
•Length is in a solid mobile-friendly range.
•No obvious spam-trigger wording detected.
Risks to fix
•Could feel more tailored with “you”, a name, or a specific context.
Variant ideas
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Email Subject Line Tester の使い方
Type a subject line to score its mobile fit, spam risk, and clarity. The tester also gives you a few quick variant ideas so you can A/B test different angles without opening another tool.
1
Enter a subject line
Type the line you plan to test in a campaign, newsletter, or outreach email.
2
Review the score and warnings
Check the overall rating plus any notes about length, spam words, or weak personalization.
3
Try variant ideas
Click a suggested variation to test a curiosity-driven or direct alternative.
よくある質問
Is a higher score a guarantee of better open rates?+
No. The score is directional, not absolute. Real open rates still depend on audience trust, sender reputation, and message relevance.
What length is best for subject lines?+
Roughly 22 to 55 characters is often a strong range for mobile readability, though context matters.