Email Subject Line Tester

How to use the email subject line tester

Using the tester is simple: just type or paste your subject line into the input field, and hit “Test.” 

You’ll instantly receive a score out of 100, along with personalized suggestions for improvement. 

You can try as many variations as you like – it’s a quick, easy way to optimize your subject lines before you hit “send.”

How is the score calculated?

Your subject line starts with a base score of 70 points. From there, the tester analyzes key factors that impact performance, from length and word choice to formatting and emotional tone.

Score factors:

 

  • Length and word count: Subject lines between 20–50 characters and 3–6 words get the highest marks. Anything too short or too long will lower your score.

  • Helpful vs. negative words: Words like “you,” “free,” or “exclusive” can boost your score. On the flip side, spammy terms like “urgent” or “buy now” will cost you points.

  • Numbers and capitalization: Including numbers can give you a small bonus. Writing in sentence case is preferred – ALL CAPS or lowercase can hurt your score.

  • Final score breakdown: Once all factors are calculated, your subject line receives a final score between 0 and 100, along with a short message describing its effectiveness.

Our subject line tester works by weighing both technical structure and marketing psychology, and gives you a well-rounded assessment designed to help you write subject lines that stand out for the right reasons. And the best part? It’s totally free!