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Free Email Subject Line Tester
Type a subject line to get an instant open-rate score, spam-word detection, emoji analysis, and improvement tips — free, no signup.
How to use Email Subject Tester
Type your subject line
Enter the subject you plan to send. The inbox preview and score update live.
Review the score
Get a 0–100 score plus character, word and emoji counts, and flagged spam/power words.
Apply the tips
Follow the suggestions to hit the ideal length, avoid spam triggers, and lift open rates.
Frequently Asked Questions
What is the ideal email subject line length?
Research consistently shows that 40–60 characters is the sweet spot for most audiences. Mobile email clients typically show 30–40 characters on the inbox preview, so place the most important words first. Gmail shows roughly 77 characters on desktop but only 30 on mobile. Shorter subjects (under 40 chars) often outperform longer ones.
Do emojis in email subjects increase open rates?
Used sparingly (1–2 per subject), emojis can increase open rates by 5–25% by making your email stand out in a crowded inbox. Overuse has the opposite effect. Not all email clients render emojis identically — test with your audience. B2B audiences are generally more conservative than B2C.
Which words trigger spam filters in email subject lines?
Common spam trigger words include: FREE, GUARANTEED, WINNER, CASH, CLICK HERE, LIMITED TIME, ACT NOW, EARN MONEY, NO COST, RISK FREE. All-caps words are also flagged. Modern spam filters use ML models, not just word lists — but avoiding these words still reduces the risk of landing in spam or the promotions tab.