Subject line testers

Top 13 Subject Line Testers To Increase Email Open Rates

Have you ever had trouble getting people to open your emails? Developing clever and attention-grabbing email subject lines can be tough for some salespeople. That’s where subject line testers can be really helpful.

But if you don’t know which tool to use, here is some help. 

In this blog post, we will study the top 16 subject line testers that will supercharge your email open rates and transform your cold email strategy. 

So, without further ado, let’s begin. 

What Is An Email Subject Line Tester?

An email subject line tester is like a friendly helper for your emails. It’s a tool that checks and helps improve subject lines. 

As you know, subject lines are super important because they’re the first thing people see when they get your email. If your subject line is boring, confusing, or doesn’t grab attention, your email might end up in the dreaded “unopened” folder.

But don’t fear! An email subject line tester can save the day. It’s like a coach for your subject lines. It checks them and gives you tips on how to make them better. It can tell you if your subject line needs to be shorter, or is boring, or looks spammy. A tester helps you create subject lines that make people want to open your emails.

Using a subject line tester, you can boost your email open rates, meaning more people will see and read your emails. If you want to send emails that get noticed, give a subject line tester a try!

Why Is Email Subject Line Testing Important?

Subject line testing is crucial for successful cold email campaigns as they help increase email open rates. Here’s why it’s so important, broken down into key points:

1. First Impressions Matter

Your email subject lines are the first things recipients see. It’s like the cover of a book – if it doesn’t grab their attention, they won’t open it. An email subject tester helps ensure your subject lines are attention-grabbing and compelling, increasing email open rates.

2. Boosts Email Open Rates

A well-crafted subject line can significantly boost email open rates. When more people open your emails, your message reaches a wider audience, increasing the chances of achieving your marketing goals.

3. Higher Engagement

Engaging subject lines pique recipients’ interest and encourage them to explore the content of your email. It can lead to more click-throughs, conversions, and better engagement with your audience.

4. Avoids the Spam Folder

Spammy or suspicious subject lines can trigger spam filters, causing your emails to land in recipients’ spam folders, where they’re less likely to be seen. Email subject testers help you steer clear of spammy language.

5. Personalization

Testing allows you to fine-tune subject lines based on your target audience’s preferences. Personalized subject lines can create a stronger connection with your recipients.

Data-Driven Decision-Making

Subject line testing provides data and insights into what works best for your audience. You can refine your email marketing strategy with time for better results by analyzing the results.

Best Email Subject Line Testers

Let’s look at some top subject line testers to boost your email marketing strategy and connect better with your audience.

1. Test Subject by Zurb

Test Subject by Zurb

It is like a tester tool that’s free to use. It checks how your sender name, email subject, and the short message at the beginning of your email (called pre-header text) will look on different types of mobile devices. It’s like a sneak peek to see if your email looks good on the latest smartphones. 

So, you can avoid situations where your email might get cut off, and important words or messages get lost when people open it on their phones, like when “Products for foolproof marketing” becomes “Products for fool…” on an older iPhone. This tool helps ensure your emails always look their best on mobile devices.

2. Omnisend


Omnisend is an email marketing platform with features to help you navigate the challenges of spam filters. This platform offers tools and strategies to ensure your emails have a better chance of landing in your recipients’ primary inboxes rather than being caught by spam filters.

Omnisend allows you to create and send emails that comply with industry best practices and spam filter guidelines. It provides features for email list segmentation, which helps you send more targeted and relevant content to your subscribers, reducing the chances of triggering spam filters. 

3. Mizy by Automizy

Mizy by Automizy

Imagine having an AI that assesses your subject lines and offers real campaign-based advice. With this tool:

  • You can significantly boost your email campaign’s open rates.
  • Increased email opens lead to higher click-through rates.
  • Improved click-through rates drive more visitors to your web pages.
  • More page visitors can translate into increased revenue from your campaigns.

4. Send Check It

Send Check It - subject line tester

Send Check It is a subject line testing tool available for free. It provides an overall score and evaluates your subject lines based on 16 criteria. These criteria cover aspects like readability, length, and content to help you create stronger subject lines.

Here’s the complete list of the 16 subject line criteria it examines:

  • How easy it is to scan.
  • The reading level required to understand it.
  • Length in terms of characters and words.
  • How it appears in a preview.
  • The sentiment conveyed (positive or negative).
  • The presence of the word “free.”
  • Any potentially spammy words.
  • Avoid spam filters.
  • The use of exclamation marks.
  • Whether you’re using all capital letters.
  • Proper use of punctuation.
  • Personalization, such as including the recipient’s name or other details.
  • Whether it includes a question.
  • Usage of all lowercase letters.
  • The inclusion of emojis.

5. Email Subject Line Tester by CoSchedule

Email Subject Line Tester by CoSchedule

This tool is designed to evaluate the effectiveness of your email subject lines. It provides real-time suggestions and improvements as you craft your subject lines, ensuring they are attention-grabbing and engaging. Additionally, it includes a headline analyzer, which is valuable for creating compelling subject lines.

Whether you’re an experienced email marketer or just starting, this tool can be a valuable resource to help you improve your email open rates and connect more effectively with your audience. 

6. Email Subject Line Grader by Net Atlantic

Email Subject Line Grader by Net Atlantic

The Email Subject Line Grader is a free tool to enhance your email subject lines. It evaluates character count, emotion, and power words to provide a performance score based on four key factors:

  • Subject Line Type: It categorizes your subject line type (e.g., “how-to” or “question”) and offers improvement tips.
  • Character Count: The tool counts characters and recommends keeping subject lines under 60 characters, as shorter lines tend to perform better.
  • Word Count: It assesses the number of words, suggesting an ideal count for maximum reader engagement.
  • Word Mixture and Balance: The tool analyzes action, emotion, and power words.,

7. Spam Check by Postmark

Spam Check by Postmark

Spam Check by Postmark is a tool that focuses on ensuring your emails avoid being flagged as spam and instead reach your recipients’ primary inboxes. It assesses your email content and subject lines to identify potential elements that could trigger spam filters.

Spam Check by Postmark can improve your email deliverability, ensuring your messages land where they should – in your recipients’ primary inbox. 

8. Refine by Moosend

Refine by Moosend - subject line tester

Refine by Moosend is a robust tool designed to elevate your cold emailing efforts. Offered by Moosend, it offers a suite of features for refining and optimizing your email campaigns, resulting in improved engagement and outcomes.

This tool employs artificial intelligence (AI) for data-backed insights, enhancing your email subject lines and content. It also supports list segmentation based on diverse criteria, ensuring emails align with specific audience segments for better relevance. 

9. Headline Analyzer by CoSchedule

Headline Analyzer by CoSchedule

CoSchedule’s Headline Analyzer is a tool designed to evaluate the effectiveness of headlines, including email subject lines. It assesses factors like word choice, structure, and emotional appeal, providing a score and suggestions to improve your subject lines.

10. Hemingway App

Hemingway App

It is a writing tool that helps you simplify and clarify your email subject lines. It highlights complex sentences, suggests alternatives, and offers readability improvements, ensuring your subject lines are clear and concise.

11. Is Not Spam

Is Not Spam - subject line tester

‘Is not SPAM’ is a free tool that helps you beat spam filters and ensure your emails reach the right inbox? It offers five important tests, including SPF, Sender-ID, DomainKeys, DKIM, and SpamAssassin checks. While primarily used for email content testing, it can also assess your subject lines. This tool is your ally in ensuring your emails aren’t mistakenly flagged as spam, increasing the chances of reaching your recipients effectively.

12. Unspam


Unspam is a useful tool for email marketers who want to ensure their emails aren’t lost in the spam folder. Even legitimate emails often end up in the spam folder by mistake, and Unspam helps prevent that. 

It checks your emails for any elements that might trigger spam filters, like certain words or phrases, and gives you feedback to help you make necessary adjustments. This way, your emails have a better chance of reaching the main inbox and being seen by your recipients.

13. MailMeteor


MailMeteor is a tool that makes sending lots of emails at once easier. Imagine you want to send a newsletter to hundreds or even thousands of people. MailMeteor helps you do this efficiently. 

It permits you to manage and send emails to a large group all at the same time. The tool is handy for businesses, organizations, or anyone who needs to communicate with a big audience through email. It simplifies the process so you can focus on creating great content and connecting with subscribers.

That brings us to the end of our list of subject line testers.

Tips To Create Email Subject Line That Increase Open Rates

Creating effective email subject lines is crucial for getting more people to open and read your emails. Here are some simple tips to help you succeed:

1. Include a Person’s Name

Adding the recipient’s name in the subject line can make the email personal and engaging. People are more likely to open emails that address them directly.

2. Be Descriptive

Tell the recipient what your email is about. A clear and relevant subject line allows them to open your email. For example, instead of “Update,” say “Exciting Product Update Coming!”

3. Keep it Short

Short subject lines are often more effective. Aim for around 40-60 characters. This way, your message is concise and easy to read.

4. Minimal Punctuation

Don’t overuse punctuation like exclamation marks!!! Or question marks??? It can make your email look like spam. Use them sparingly and only when necessary.

5. Use Emojis Carefully

Emojis can add a fun touch to your subject line, but keep it simple. Make sure they match the tone of your email, and use them in moderation.

6. Power Words

Power words are strong, attention-grabbing words that evoke emotion. Words like “exclusive,” “free,” “limited time,” and “urgent” can make your subject line more compelling.

7. A/B Test

Consider A/B testing your subject lines. It means sending two versions of your email with different subject lines to a small group and seeing which one performs better. This way, you can use the most effective subject line for the rest of your recipients.

Remember, a strong subject line is about getting people to open your email and email deliverability. These tips can increase your chances of higher open rates and better email deliverability.

Boost Your Email Open Rates with These Top 16 Subject Line Testers

In the world of cold emailing, where catching your audience’s attention is a constant challenge, subject line testers prove to be helpful. These 13 subject line testers offer a range of features, from analyzing subject line content to checking for spam triggers. You can use the testers to fine-tune your email subject lines, making them more catchy and increasing your open rates.

As you explore and utilize these tools, remember that crafting effective subject lines is an ongoing process. Continuously test and refine your approaches to find what resonates best with your audience. 

We hope these tools will prove to be valuable assets on your journey to improving email open rates and achieving greater success in your email marketing campaigns. 

Happy testing!


1. How Do Email Subject Line Testers Work?

Email subject line testers analyze various elements of your proposed subject line, such as length, word choice, sentiment, and sometimes even industry-specific keywords. After the analysis, the tool will usually give you a score or rating and suggestions for improvement.

2. Are Email Subject Line Testers Accurate?

The accuracy of subject line testers can vary depending on the algorithm and its data quality. While these tools provide a good starting point for optimizing your subject lines, they are not foolproof. It’s always a good idea to A/B test your subject lines.

3. Is It Worth Investing in a Premium Email Subject Line Tester?

If you’re running large-scale cold email campaigns, investing in a premium tool could provide you with what you need to optimize your campaigns effectively. On the other hand, if you’re a small business or just getting started, a free tool may suffice for your current needs.






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