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Email Subject Line Tester

Score your email subject lines on length, power words, spam triggers and emoji use — get a score and specific improvement tips to boost open rates.

Length check Power words Spam trigger detection Emoji analysis Preview simulation Improvement tips
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Free · No credit card · 50 credits/day

What gets scored

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Character length

40–50 characters is optimal for mobile preview. Under 20 or over 60 chars both underperform. The tool previews how your subject truncates at different screen sizes.

⚡

Power words

Counts emotionally charged words that drive opens: urgency ("today only"), curiosity ("nobody told you"), exclusivity ("members-only"). 2–4 is the sweet spot.

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Spam trigger check

Flags words and patterns that trigger spam filters or damage sender reputation — FREE in all caps, multiple exclamation marks, "act now", currency symbols.

😊

Emoji analysis

Checks whether emoji placement and count is appropriate. Single relevant emoji can lift opens by 5–10%. Multiple emoji reads as spam.

👁️

Preview simulation

Shows how your subject line appears in Gmail, Outlook and Apple Mail preview panes — including truncation on mobile vs desktop.

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Improvement tips

Specific, actionable suggestions: "add a number", "front-load the key phrase", "replace [word] with a stronger synonym" — not generic advice.

Frequently asked questions

What is a good email open rate?

Overall average across industries (2024): 21–23%. High performers: government (28%), nonprofit (26%), education (25%). Lower: e-commerce (15–18%). More important than industry average is your own trend — improving from 18% to 22% is meaningful progress. Click-to-open rate (CTOR) is a better effectiveness measure than raw open rate.

What length should an email subject line be?

40–50 characters for mobile preview. Desktop shows 60–80 characters. Mobile preview shows 30–40. Front-load key information in the first 40 characters to ensure it's visible on all devices. Subject lines under 20 or over 60 characters both perform below average. Sweet spot: 6–10 words.

What words trigger spam filters in email subject lines?

Common triggers: FREE (especially in all caps), URGENT, Act Now, Click Here, Make Money, 100% guaranteed, Winner, Claim your prize, $$$, excessive punctuation (!!!), ALL CAPS. Modern spam filters use machine learning, so combinations of signals — poor sender reputation + spam words + high image-to-text ratio — filter emails, not a single word alone.

Should I use emoji in email subject lines?

One relevant emoji can increase open rates 5–10%. Avoid: emoji that render as boxes in some clients (☎), multiple emoji (💰💰💰), emoji that conflict with a professional tone. B2B audiences often respond better to emoji-free subject lines. Always test rendering across Gmail, Outlook and Apple Mail.

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