Free tool
Email Subject Line Tester
Score your subject line before you send. Get instant feedback on length, spam words, capitalization, punctuation and personalization.
Your subject line decides whether your email gets opened or ignored. This free email subject line tester grades your subject on the factors that influence open rates: character length, word count, spam trigger words, all-caps shouting, punctuation abuse, emoji use, numbers and personalization. You get a 0 to 100 score with a clear checklist of what passed and what to improve. Everything runs in your browser, so test as many variations as you like.
How to use the subject line tester
- 1
Type or paste your subject line into the field above.
- 2
Click "Test it" or press Enter to run the analysis.
- 3
Read your score out of 100 and the detailed checklist below it.
- 4
Rewrite the parts that got a warning, like spam words or all-caps.
- 5
Test a few variations and pick the one with the strongest score.
Frequently asked questions
What makes a good email subject line?
A good subject line is short, specific and written for one reader. Around 30 to 50 characters, no spam trigger words, sentence case rather than ALL CAPS, and ideally a concrete detail like a number or the reader's name. Above all it should promise something the email actually delivers, because misleading subjects destroy trust and future opens.
How long should an email subject line be?
Most email clients show about 30 to 50 characters on mobile and slightly more on desktop, so that range is the safest. If your subject is longer, put the most important words first so the visible part still makes sense when truncated.
How is the score calculated?
The tester runs eight weighted checks: length, word count, spam trigger words, capitalization, punctuation, emoji use, numbers and personalization. Each passed check adds its weight, up to 100. The score is a heuristic guide, not a guarantee, so use the checklist to understand each recommendation.
Do emojis in subject lines hurt open rates?
Not necessarily. One relevant emoji can help your email stand out in a crowded inbox. Several emojis, however, pattern-match to promotional spam for both filters and readers. If your audience is professional, test with and without one.
Does personalization in subject lines really work?
Yes, personalized subject lines consistently see higher open rates. Using the recipient's name, company or another attribute makes the email feel written for them. With Mail Merge for Gmail you can insert any column from your Google Sheet as a merge tag directly into the subject line.
Is my subject line stored anywhere?
No. The analysis runs completely in your browser. Nothing is sent to a server, logged or stored, so you can test unreleased campaign ideas safely.
Great subject lines deserve great sending
Personalize subject lines with merge tags and send campaigns right from Gmail with Mail Merge.