How to Use the Email Subject Line Tester

1. Type your subject line in the input field — the score and feedback update instantly as you write.
2. Check the inbox previews — see how your subject line looks when truncated on a mobile device (40 characters) and Gmail desktop (60 characters). Front-load your key message.
3. Read the feedback — each check flags specific issues or strengths: spam trigger words, length, power words, emoji usage, numbers, and personalisation tokens.
4. Refine your subject line until you reach a score of 65 or higher. Test multiple variations and pick the strongest one.

What Makes a Strong Email Subject Line?

• Length: 40–60 characters — long enough to be descriptive, short enough to display fully on most email clients. Mobile typically cuts off after 40 characters, so put your hook first.
• Avoid spam trigger words — words like “free”, “winner”, “guarantee”, “act now”, and “click here” are associated with spam. Even one can affect deliverability.
• Use power words — action-oriented words like “discover”, “save”, “new”, “you”, and “now” create a sense of relevance and urgency that lifts open rates.
• Include a number — “5 tips” or “save 30%” are more specific and credible than vague promises. Numbered subjects typically outperform non-numbered ones.
• Ask a question — questions create curiosity and a natural pull to open the email for the answer.
• Use personalisation — including the recipient’s first name (via a merge tag like {first_name}) typically increases open rates by 10–20%.
• Use emoji sparingly — one relevant emoji can improve open rates, especially on mobile. More than two risks looking spammy.
• Avoid excessive punctuation — multiple exclamation marks (“!!!”) are a strong spam signal and reduce credibility.

Email Subject Line Length by Email Client

• iPhone (iOS Mail): ~35–40 characters before truncation in the inbox list view.
• Android Gmail app: ~40 characters visible in list view.
• Gmail desktop: ~60 characters before the subject line is cut off in the inbox.
• Outlook desktop: ~60–70 characters depending on screen width.
• Apple Mail (macOS): ~60–80 characters depending on window width.

The safest strategy is to keep your subject line under 50 characters and place your most important words in the first 35–40 characters. This ensures the key message is visible regardless of the device.

Frequently Asked Questions

What is a good email subject line score?

A score of 65 or above is good. 80 or above is excellent. Scores below 45 indicate significant issues — usually too many spam words, poor length, or missing engagement signals like power words or numbers.

Does a high score guarantee better open rates?

Not guaranteed — open rates also depend on your sender reputation, list quality, send time, and audience segment. A high score means your subject line follows best practices that are statistically correlated with better performance. Always A/B test your subject lines when possible.

What are spam trigger words?

Spam trigger words are words or phrases that email spam filters commonly associate with unwanted mail — such as “free”, “winner”, “guaranteed”, “act now”, and “click here”. Using them doesn’t guarantee your email will be filtered, but it raises the spam score and reduces deliverability, especially combined with other spam signals.

Should I always use personalisation?

Personalisation is highly effective when your list data is accurate and up to date. Incorrect personalisation (“Hi {first_name}”) is worse than no personalisation at all. Use it when you’re confident in your data quality.

Is this tool free?

Yes, completely free with no account required. All analysis happens in your browser — no email data is sent to any server.

Explore more free tools for marketers: UTM Builder, Google Ads Character Counter, Word & Character Counter, and SERP Preview Tool.