Free tool
Email subject line tester
Type a subject line and see how it looks on desktop and mobile, how long it is, and whether it is full of spam triggers — before anyone sees it.
Readability check
- Start typing to see suggestions.
Score
Higher is better
Waiting for a subject line…
A good subject line is short, personal and specific.
Inbox preview
Desktop · shows ~60 characters
Your subject line appears here…
Mailster <no-reply@mailster.co.in>
Mobile · shows ~35 characters
…
Mailster
What the score looks at
The score is a rough guide, not gospel. It checks the usual traps that hurt open rates.
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1
Length
Keep it under ~50 characters so nothing gets cut off on mobile. Short beats clever.
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2
Spam triggers
"Free", "guarantee", "act now" and excess punctuation push mail toward the spam folder.
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3
Clarity
ALL CAPS and clickbait feel like spam. Specific, personal subjects get opened.
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4
Device fit
Over half of email is read on phones. If it reads well at 35 characters, you win.
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