What is the best e-mail subject line tester tool?

Use AI to write high-performing marketing copy faster. 10x faster.

Test neuroflash's AI copywriter with the free plan.
Most marketeers use email campaigns to reach to their target audience, but many do not know the importance of a catchy subject line and what an email subject line tester does exactly. In this blog article, I will explain to you these points and name a few subject line tester tools for you to work with.
Share This Post

What is an email subject line tester?


e-mail subject line tester tool neuroflash


An email subject line tester is a tool that analyses your subject line for your next email campaign and then tells you if and what you should improve. Most tools check for spam markers and tell you what you could change in order to boost your open rate by using data collected by partners or the internet to make determinations. Different testers check for different factors:

  • spammy words
  • punctuation 
  • length
  • grammar
  • emotionality

I will get later into the different email subject line tester tools

Why is email marketing important?

e-mail subject line tester ROI
Source: Neil Patel


  1. Segmenting is easy: Nowadays, it is important to address each target audience as focused as possible. The easiest way to do this is to use email marketing campaigns as you can exactly segment your subscribers emails and ensure that only customers are getting your email, if it is relevant to them. This increases your effective click rate and decreases scatter loss.

  2. Timing is everything: Subscribers receive your emails during anytime of day. The good thing is, that they don’t have to immediately open, but they can have a read when they have time for it and are more focused, so they are likely to absorb more information than let’s say during a TV-spot, when most people are on their phones or go to the bathroom.

  3. Informing your customers: If people signed up to be a subscriber, they are willing to get your emails in order to get more information about your company. You are able to spread as much information whenever you want to your target audience.

  4. Low costs: You can reach a large audience for a very low cost. If you send out between 10,000 and 50,000 your cost per mille (cost per thousand) is $10. So each email would cost you around $0.01. If you send out more, it is going to be cheaper for you. 

  5. Long lifespan: people keep email addresses for a long time – in average does one person keep his/her email address for 10 years. So, once you have the email address from potential customers it is very likely that they still use their email address.  


Why are email subject lines key?


e-mail subject line tester statistics
Source: anchorcomputer


We all know this feeling: flooded inboxes full of shiploads of newsletter. But which ones should I open? This is the question many people ask themselves every day. The first thing that catches most recipients eye is the newsletter subject line and depending on that they decide whether they should open the email or not. Therefore, your open rate and your klick rate also depend on how catchy your subject line is. 

Sometimes even changing the wording of your subject line can have a big effect on the recipient’s emotionality. For example,  neuroflash changed one wording of a customers subject line and the open rate increased by 5%. In this case the word “safety” made a crucial difference. Most people associate this word with certain emotions – perhaps the feeling of being protected or wanting to be protected – and thus are more convinced to open the newsletter. 

If you are wondering about how to craft your subject line in a way that convinces your subscribers you can have a look at this blog article


The best email subject line tools


  1. neuroflash

    neuroflash does not test your e-mail subject line, it creates them from scratch. You do not have to worry about any writer’s block, pressure to be creative, or pressure of time. Our AI generates subject lines depending on a few keywords and the mood you want it to be in. Afterwards, it even validates the one you chose and tells you by how much the opening rate of that particular subject line will increase. If you were looking for an excellent subject line tool you have to look no more! Do you want to write creative subject lines with us? Then you should try out our free test version!


  2. SubjectLine
    This tool analyses your subject line for spammy word and gives you information on what to change, so you can increase your open rate. They use data collected from partners in order to produce real-time, useful suggestions.


  3. CoSchedule’s Headline Analyzer
    Within the marketing communities this tool is known as one of the best headline testing tools to use. Even though headlines and subject lines are to a small degree different, they incorporate many same features, such as testing for grammar, length, and structure.


  4. Email Subject Line Grader
    Is the go-to-tool if you want to check for emotionality in your email subject line, which is an important factor considering the fact that many readers open emails based on emotion. This tool also checks for length and grammar.


  5. Zurb TestSubject
    A lot of subscribers are going to check their emails from their mobile phone, so it is key to design your email to be mobile compatible, especially the subject line. This is what this tool can do for you.


How to choose the best email subject line tool?


e-mail subject line tester decision
Source: freepik

Nowadays, most email marketing software tools are designed to not only send emails and newsletter, but to carry out many other different functions. We already went over the importance of email subject lines. Here is an overview over other important features:

  1. Spam Filter Test-Email
    If your email ends up in spam folders your reputation will be worse and you will miss out on potential profit. Therefore, it is really important that you use a tool that checks how spam filters estimates your email and if you should change it.

  2. Test HTML validation
    One important factor when it comes to your email campaign is that the images and other media in your email loads correctly regardless of whether the reader uses a phone or laptop, whether the reader uses yahoo or Gmail.

  3. Preview email design and layout
    Prior to sending your email it is crucial that you check your formatting in your email design. The first impression is the most important one, so if customers already decided to open your email, but then the formatting is off, it might leave you with a bad reputation. Also don’t forget to adjust your email design to be mobile compatible as many subscribers check their emails on their phone.

  4. Check sender reputation
    You need to watch out for your sender scores before sending out emails because your subscriber’s email service uses algorithms to check for different factors that puts your email to the spam folder. Reputation of the sender is one factor, which is why you should use a tool that checks for this.

  5. Subscriber verification
    You should use a tool that shows you whether the email is sent to a valid email address or an invalid one. If you keep on sending emails to an invalid email address it is going to cost you money and time, and it will have an effect on your opening rate.  It can also be bad for your reputation and therefore make your emails look like spam.

Use AI to write high-performing marketing copy faster. 10x faster.

Test neuroflash's AI copywriter with the free plan.

More To Explore

Content Creation

New Professional Plan – ChatGPT Pricing

What is the new ChatGPT price and what does it offer? What’s next for the popular chatbot? In this article you will learn what changes with the new price and how you can react to these changes.

Content Creation

ChatGPT Update: The new ChatGPT Professional

ChatGPT Professional is the new feature of the well-known and popular ChatGPT. In this article you will learn what to expect from ChatGPT Professional and how to get access to the new plan.

Test your magic pen in action:

Step 1: Choose a text type
Step 2: Enter briefing

No more writer's block


Use our AI to generate new content within seconds for free.