9 Free Subject Line Testers To Drive Open Rates 
One of the key parts of a successful email campaign is the subject line. It’s the first element that appears in your subscribers’ mailboxes and increases open rates.
Let’s see some impressive stats: 64% of email recipients decide whether to open an email based on the subject line, and 69% also said that they move emails to spam based on them.
So if you’re worried about the impact of your subject lines, no matter how great your copywriting is, you can use a subject line tester for maximum performance. In this guide, you’ll find first-class tools to make this process a piece of cake.
Let’s take it from the top!
What Is An Email Subject Line Tester?
Subject line testing tools provide helpful information regarding the efficiency of subject lines to help businesses increase their email open rates. They’re usually provided by email service providers (ESPs) and similar marketing platforms.
In brief, most of these tools test:
- Spammy words: It detects words likely to transfer your email to spam, such as 100% free, urgent, buy now, etc.
- Word count: Testers suggest the optimal character length to optimize your subject line for all devices.
- Sentiment: It explains the emotional effect of the subject line on the audience through powerful words and emojis.
- Preview: Some testers show how the subject line appears on different devices to ensure maximal results.
Let’s explore some top-notch subject line testing tools that can contribute to your email marketing success:
1. Refine by Moosend
Best Feature: Data per industry
Moosend’s Refine is a free email subject line testing tool that helps businesses drive higher open rates and secure a steady deliverability score. One of its main pros is that it provides data per industry for a certain number of subscribers, enabling users to stand out from the competition.
Once you write your subject line, you’ll see how it performs for your industry. If there’s room for improvement, you’ll find some guidelines to optimize it and capture your subscriber’s attention.
Here, the platform suggests email segmentation for maximum personalization and performance:
Apart from this standalone tool, Moosend provides an additional checker inside the software with thorough information. So if you’re looking for a holistic email marketing solution to do it all, it’s an excellent choice for you.
Have a look at this Moosend subject line report:
Best Feature: Scannability
Omnisend offers one of the best email subject line testers, providing users with various information to achieve higher metrics. First, apart from a generic subject line score, it shows character count and wording insights.
Moreover, the scannability feature helps users get past spam filters. Finally, they offer an additional section with diverse subject line types to get inspired for your next campaign.
3. Send Check It
Best feature: Intuitive tester
Send Check It is another free testing tool that can help you power up your email marketing strategy showing you the way to optimal subject lines. You need to provide your first name and email address for their helpful insights.
In a nutshell, you’ll get a readability score, character count, wording, and punctuation suggestions. It also reports on emoji count and offers capitalization remarks to avoid spam filters and draw the readers’ attention at first sight.
Best feature: Spam filter immunity
CoSchedule is a content marketing software well-known for its headline analyzer, which also offers a tester to build great subject lines. CoSchedule requests your personal information to give you a thorough report.
You can see an example of the email subject line analysis in the above image. It includes suggestions regarding wording and phasing, character length, and a dedicated preview section to see how your subject line appears on different devices.
5. Email Subject Line Grader
Best feature: Word mixture
Email Subject Line Grader is a free subject line tester with basic features for more experienced copywriters. It provides users with limited suggestions that can still do the trick.
For example, it provides users with wording suggestions to make subject lines more specific if needed, such as asking a question to make it more indulging. You’ll also find more details about the word and character count.
If you’re looking for quick ways to optimize your subject line and increase the open and click-through rates of your email marketing campaigns, you can use MailMeteor’s tool.
In short, you’ll get ready-made templates with copy that will result in better performance to reach out to your audience faster with the right email messages. No login is required.
7. Test Subject by Zurb
Best feature: Mobile responsiveness
So if you need a quick check to see how the front-facing parts of your email campaign appear on different devices, this tool is suitable for you.
8. Grademyemail by Netcore
Best feature: eCommerce-friendly
Grademyemail has another email subject tester that works best for the retail industry and can give you insights on improving your subject line and preheader text.
In short, you’ll receive a report on sentiment analysis and spam probability, including suggestions for improvement, such as word and character count.
9. Spam Check by Postmark
Best feature: Spam score
If you need a free tool to ensure that your emails get past spam filters, you can use Spam Check by Postmark. It’s not limited to subject lines; instead, you can include your whole email content, and it will present you with a spam score to improve it.
Hence, Spam Check helps you interpret SpamAssassin’s score minus the hustle.
Tips For A Successful Email Subject Line For Higher Open Rates
Long story short, most email subject line testers are free and accessible to everyone via popular email automation or similar tools. But if you want to ensure that your subject line receives a high score before testing it, here are some tips for you:
- Keep it straightforward: Write short and descriptive copy with relevant but limited keywords.
- Personalize it: Add the recipient’s name and use email segmentation to personalize your campaigns.
- Avoid spammy words: For example, free, pay, and characters like % may flag your email as spam and repel subscribers.
- Run A/B Testing: Explore which subject line version works best for your audience.
- Optimize for mobile devices: Ensure your subject line looks stellar on every device.
- Combine with sender name/preheader text: Optimize the additional elements that appear on the mailbox to maximize open rates.
Subject Line Tester Tools FAQs
Do you still have questions regarding subject line testing? We have some quick answers for you:
1. How do you test a subject line?
You can use a dedicated subject line testing tool, e.g., Refine by Moosend, that provides suggestions to improve your subject line and avoid spam filters.
2. What is the best subject line tester?
Here are some first-class testers to check: 1) Refine by Moosend, 2) Omnisend, 3) Send Check It, 4) CoSchedule 5) Email Subject Line Grader, 6) Mailmeteor, and 7) Test Subject by Zurb.
3. How long should a subject line be?
According to Marketo, 41 characters usually do the trick, but it primarily depends on the devices of your subscribers.
4. What subject lines end up in spam?
Avoid spammy words and characters, such as free and $, excessive uppercase letters and keywords, and use punctuation wisely – e.g., delete exclamation marks.