Your subject line is your subscriber’s first point of contact with your email. It needs to capture their interest with enough vigor to get them to open the email and read through its contents. Without a compelling subject line, your entire email campaign will likely fail.

Thankfully, you can now use a subject line tester to help you develop persuasive email subjects. Such tools won’t just help boost open rates but also lower the risk of being marked as spam. Consequently, you improve your email deliverability and maintain a good sender reputation, which is essential for the success of your email marketing efforts.

Why use an email subject line tester tool?

Crafting good subject lines is both an art and a science. It’s a combination of cleverness, creativity, and data: something tried, tested, and based on historical data.

For example, data shows that subject lines composed of around six words have the highest open rates and that including the recipient’s name improves open rates by almost 30%.

On the other hand, using the word “Sale” is detrimental to your success metrics while “Sales” can boost your open rates by up to 4%.

Confusing, right?

But if you don’t get it right, you could lose the interest of the 47% of your subscribers who open emails based solely on their first impression of your subject line.

Sure, you can study all available data on what could work for your campaigns. But you can also simply use subject line testers that do all the research and hard work for you. Using these tools, you can easily craft subjects that not only pass spam filters but will also make your subscribers more likely to click and read.

Here is our selection of the best email subject line tester tools you should consider for your next email campaign:

  1. Omnisend
  2. Net Atlantic
  4. CoSchedule
  5. Send Check it
  6. Automizy
  7. Moosend
  8. Alchemy Worx

Omnisend – Email Subject Line Tester

omnisend email tester

Price: Free

Run your email subject line through Omnisend’s Email Subject Line Tester and it’ll give you a score (percentage) on how effective it might be. Best of all, it evaluates your subjects based on a variety of data-proven concepts and gives you recommendations to improve your score.
It starts with the basics, which are length and wording. Apart from optimal character and word counts, the tool gives you suggestions on which words are helpful and which ones should be replaced with safer alternatives.

Then, it points out what puts you at risk of being marked as spam as well as what you can improve on in terms of scannability.

Lastly, it gives you a preview of how your subject might appear on desktop and mobile devices.

Net Atlantic – Email Subject Line Grader

net atlantic email tester

Price: Free

The Email Subject Line Grader by Net Atlantic scores your subject based on three major criteria:

  1. Subject Line Type: evaluates the general impression that your subject line will likely give your recipients. Ideally, you’ll want to avoid being neutral or too general. What you want is to make a strong statement.
  2. Character & Word Count: Net Atlantic tool favors subjects with lengths of 50 to 65 characters and a maximum of 7 words
  3. Word Mixture & Balance: the tool makes recommendations on whether you should add more words that affect emotion, power, or action in order to improve your chances of getting a good response.

subject line email tester

Price: Free might give an initial impression of being too cluttered and scammy, but it’s actually a remarkably useful tool. It gives your email subject line a score out of 100 points and offers you detailed recommendations to improve your campaign’s results both in terms of deliverability and marketing effectiveness.

According to, its scoring system is based on data gathered from over 3 billion messages sent through its clients and partners. The tool checks your subject line against over 800 rules and points out issues that might cause you to have problems with spam filters or lower your open rates. Additionally, it tells you what you’ve done right so you know exactly what you should keep and what you should change in order to craft the best subject line for your campaign.

CoSchedule – Email Subject Line Tester

coschedule email subject line

Price: Free

Coschedule’s email subject line tester tool grades your subject line based on a 100-point system. Apart from character and word lengths, it checks for scannability and reading grade level. The easier it is to read and comprehend, the higher your score. Other critical issues that it checks are the presence of undesirable words like “Re:,” “Fw:,” “Free,” and words that are either regarded as “spammy” or could make Gmail classify your email as Promotional.

The CoSchedule email tester tool also checks for excessive and undesirable punctuation (the fewer, the better especially for exclamation points), proper capitalization (using all caps is risky while lowercase can give your email a more personal feel), personalization, and use of emojis. It also provides a useful preview of how your subject line is likely to appear on both desktop and mobile.

Send Check It – Email Subject Line Tester

send check it subject line

Price: Free

The Email Subject Line Tester by Send Check It compares your line against more than 100,000 marketing emails and scores it based on what has been proven to work. It gives you both a letter and number score along with recommendations on how to improve your grade (and, consequently, your subject’s likelihood for success).

Similarly to the CoSchedule tester, the tool by Send Check It checks for length, reading grade level, and scannability. Then, it gives you a preview of how it might appear on both mobile and desktop. If you’re interested in a more in-depth analysis, it also conducts a sentiment analysis to determine whether your proposed subject line seems positive, negative, or neutral. Additionally, it checks for certain words to avoid, as well as the proper use of punctuation, capitalization, personalization, and emojis.

Automizy – Mizy’s Free Email Subject Line Tester

automizy email subject line

Price: Free

Like many similar tools, Mizy’s Free Email Subject Line Tester by Automizy scores your subject against a 100-point system. Then, it gives you several email subject templates you can use to achieve the best results from your email campaigns. Instead of the supposed email subject line testing best practices and benchmarks, the scoring system and subject line template recommendations are based on artificial intelligence.

Mizy, Automizy’s AI, continuously scans through and analyzes thousands of email campaigns. Through deep learning, it makes conclusions on what works and what doesn’t. So, all you’ll have to do is fill in the blanks and keep testing until you’ve reached the score you’re satisfied with and you’re ready to push through with your campaign.

Moosend – Refine: Subject Line Tester

moosend email subject line tester

Price: Free

Refine by Moosend is a subject line tester that predicts your open rate based on the subject line you provide. Apart from your proposed subject line, the tool asks you to select your industry and subscriber number. Using that information, it compares your predicted performance with the average open rate in your industry so you know if you’re on the right track, or if there’s still a little room for improvement.

Apart from an open rate prediction and a comparison with benchmarks in your industry, the Refine tool also makes recommendations to make the most of your subject line. That might include anything emojis, improving personalization, changing percentages to dollar amounts, and giving a sense of urgency. The best part is it gives you an estimate of the impact each suggestion will make on your open rate.

Alchemy Worx – Touchstone Subject Line Test

alchemy worx email subject line tester

Price: Starts at $19.99 (1 Day Unlimited)

Rather than testing your subject line against known best practices and industry averages, Touchstone by Alchemy Worx simulates your subscriber base to predict impressions, clicks, and conversions. This is arguably better than performing a live A/B test, which usually involves less than 10% of your actual subscribers. A virtual test allows you to predict performance using your entire database. Through this process, you wouldn’t lose any opportunities because none of your subscribers will actually receive anything until you’re satisfied with the predicted performance and push through with your campaign.

Touchstone is a paid tool, which might not be ideal for smaller campaigns but could definitely provide value to businesses that rely heavily on their email subscribers to generate revenues. Depending on the account tier you sign up for, you could also perform segment testing on up to 10 segments of your subscribers. This tool also enables you to compare your subject lines with approximately 21 billion emails in their database. Plus, you can test ten different versions of your subject at a time, allowing you to find the most effective version in mere seconds.

Wrapping up

The best subject line tester for your campaign really depends on your audience and your goals. While some are best for passing spam filters, others focus on an effective structure – like ideal character lengths and mobile-friendliness. No matter which tool you choose, it should help you boost your open rates, which inevitably leads to better sales and better brand engagement.