This week, I’m recommending CoSchedule’s Subject Line Tester.
CoSchedule’s Email Subject Line Tester is a free online tool designed to give you instant feedback on your subject lines. It analyzes your headline against a database of successful emails, providing a score and actionable recommendations to help you boost your open rates and overall email campaign performance.
How to Use the Tester in 5 Simple Steps
- Type Your Subject Line: Simply enter the subject line you’re considering into the provided field on the CoSchedule website.
- Get Instant Analysis: The tool immediately processes your input and provides an analysis.
- Receive a Score & Breakdown: You’ll get a numerical score (typically out of 100) along with a detailed breakdown of its strengths and weaknesses.
- Review Suggestions: The tester provides specific suggestions for improvement, such as adding power words, emotional words, or adjusting its length for optimal readability.
- Refine and Test Again: Tweak your subject line based on the feedback and re-test until you achieve a score you’re happy with. It’s an iterative process that leads to better results!
The beauty of CoSchedule’s tester lies in its comprehensive analysis. It doesn’t just give you a score; it breaks down your subject line’s effectiveness across several critical factors. You’ll see how your subject line performs based on:
- Overall Score: A quick check of your subject line’s predicted performance.
- Word Balance: It assesses the mix of common, uncommon, emotional, and power words, guiding you towards a more impactful blend.
- Length: Provides recommendations for ideal character and word counts to ensure readability on various devices.
- Sentiment: Analyzes whether your subject line conveys a positive, negative, or neutral tone.
- Spam Triggers: Helps you identify and avoid words or phrases that might trigger spam filters.
- Preview: Shows you how your subject line will likely appear in common inbox displays, so you can catch truncation issues.
- Keywords: Highlights strong keywords that resonate with your audience and search intent (if applicable).
Best Practices for Writing Effective Email Subject Lines
While the tester is fantastic, remember these timeless best practices that the tool helps you optimize for:
- Be Clear & Concise: Get straight to the point. Subscribers should know what your email is about at a glance.
- Create Urgency/Scarcity (where appropriate): Phrases like “Limited Time Offer” or “Don’t Miss Out!” can drive immediate action.
- Personalization: Using the recipient’s name or other relevant data can significantly boost engagement.
- Pique Curiosity: Ask a question or hint at valuable information to encourage an open, but always deliver on that promise inside the email.
- Focus on Benefit: What’s in it for the reader? Highlight the value they’ll gain by opening your email.
- Use Emojis Sparingly: Emojis can boost open rates, but use them thoughtfully and know your audience. Too many or irrelevant emojis can look unprofessional.
- A/B Test Relentlessly: The best way to know what works for your audience is to test different subject lines against each other.
Curious about the effectiveness of this blog post’s title as an email subject line, I entered it into the tool. Take a look at its performance score below:

Here’s an improved score with a different heading; however, it has too many words.



