10 Best Subject Line Tester Tools to Boost Email Open Rate

Isn’t it annoying when you have everything perfectly lined up to send out a mail, only to be stopped in your tracks by a lack of a great subject line? Given that subject lines decide whether a mail is opened or sent packed to the trash, it is essential that you get them right.

This simple line has so much magic to it, that if you get it right, you can knock your email campaigns out of the Hogwarts’ park!

Don’t believe in magic?

Then we will let these numbers speak:

  • The word “Sales” increases the open rate by 4% while “Sale” decreases it by 2%
  • Email subject lines that were personalized by including a name boosted open rates by 29.3%
  • 68% of email recipients report email as spam based solely on the subject line
  • Subject lines with 1-5 words have a 16% open rate, 6-10 words have a 21% open rate and 11-15 words have a 14% open rate.

Your subject line has to be simple yet intriguing, has to be packed with power words, should not be too long, etc. for your prospect to open the mail.

That is quite a task, isn’t it? To get the balance just right.

But let’s say, you do.

The next question that comes up is, “Is the subject line that is crafted good enough?”

You are just a little unsure if it is good enough to send out to your prospects. Maybe, you wish you could send out a mail with that subject line, check whether it works or not and travel back in time to change it.

Well, unless you lived in a Richard Curtis movie, that is not possible. 

Enter, Subject Line Tester Tools.

Subject Line Tester Tools can be used to analyze your email subject lines and give you feedback on how effective they are. Here are some of the best email subject line tester tools that will help make your email subject lines irresistible.

Best Email Subject Line Tester Tools in 2022


Refine by Moosend is an AI-powered email subject line tester tool that will show you the open rates of your subject line and compare it to industry standards. Refine’s best feature is that it will provide you advice on how to increase open rates through personalization and make the most of your character limit.

screenshot of landing page of Refine, the free subject line tester

What the tool does: Analyze and compare the rating of your subject line to the industry standard.

How to test: Choose your industry first, then type your subject line into the tab.

Price: Free


Mailmeteor is one of the fastest subject line tester tools which would give you a score based on checks made at multiple levels: length, number of words, number of topic mark and exclamation points, presence of emojis or spam words. Its best part is that it provides alternative subject lines using GPT-3.

Screenshot of Email Subject Line Tester Tools - Mailmeteor

What the tool does: After analyzing your subject line, Mailmeteor gives it a score.

How to test: Enter your subject line in the tab

Price: Free

Test Subject                                                                                                                                    

Ever wondered how the mail you send is displayed in your prospect’s phone? In case you hadn’t realized, it varies from device to device. This tool shows you how your subject line is displayed on different mobile phones.

Screenshot of Email Subject Line Tester Tools - Test Subject

What the tool does: Show how your mail is displayed on different mobile phones

How to test: Enter your subject line in the tab

Price: FREE

Email Subject Line Grader

This is one of the simplest Subject line tester tools out there. The tool analyzes your subject line based on many factors to determine how captivating it is in the eyes of your prospects. All you have to do is enter your line in the tab and it gives its opinion based on the type of subject line along with a rough assessment based on your subject line’s:

  • Word mixture and Balance
  • Word count
  • Character count
  • Power words
Screenshot of Email Subject Line Tester Tools - Email subject line grader

What the tool does: Give a score after assessing your subject line

How to test: Enter your subject line in the tab

Price: FREE


Subjectline.com is Mr. No-nonsense when it comes to testing email subject lines. This tool helps marketers to test any subject line. The results are based on over a billion email messages that have been sent and tracked via subjectline.com’s partners and clients. It evaluates filtering and deliverability issues, if any, as well as marketing and performance-related concerns.

Screenshot of Email Subject Line Tester Tools - SubjectLine.com

What the tool does: A thorough assessment of the subject line

How to test: Enter your details and fill out the form to view the results

Price: FREE

Email Subject Line Tester

Email Subject Line Tester is a powerful and easy-to-use tool that helps you check if your subject lines contain words that are considered spammy.

The tool checks for different parameters, such as reading level, sentiment, and personalization, and gives you a score out of 100 based on which you can decide to use or change the line.

Screenshot of Email Subject Line Tester Tools - Email Subject Line Tester

What the tool does: Analyzes your subject line to see if there are spam words

How to test: Enter the subject line and simply click ‘Test Subject Now’

Price: FREE


This tool ensures that your subject lines do not contain any trigger words that might make it get marked as spam by one of those filters used by your prospects After spending so much time and efforts on your mail, the last thing you want is for it to be tossed down the trash because the spam filters assumed your mail to be spam.

Screenshot of Email Subject Line Tester Tools - IsnotSPAM

What the tool does: Analyzes subject lines to ensure it is spam free

How to test: Send a mail of your content to the mail address mentioned to get a detailed report of your content.

Price: FREE

EMV Analyzer

English language has about 20% of words that can be classified as Emotional Marketing Value (EMV) Words. These are words that invoke an intellectual or empathetic or spiritual side of the readers. This tool gives an analysis of your subject line based on the EMV.

Screenshot of Email Subject Line Tester Tools - EMV Analyzer

What the tool does: Analyze your subject line based on its Emotional Marketing Value

How to test: Enter your subject line in the tab

Price: FREE

Hemingway App

Ernest Hemingway was known for his straightforward writing style. “The lady doth protest too much” in a Shakespearean play would become “She is opposing it strongly” in an Ernest Hemingway novel. The tool does exactly that. It analyzes how an intermediate Homosapien comprehends your subject line (Can an average Joe understand what you are saying)

Screenshot of Email Subject Line Tester Tools - Hemingway App

What the tool does: Points out the complexities in your text

How to test: Copy-paste your content into the tab

Price: FREE

Headline Analyzer

The Headline Analyzer tool by Coschedule is one of the must-have tools when it comes to subject line testing. The tool while it was built for headlines of articles and blogs, it works just as fine for our purpose of testing email subject lines. It gives an overall assessment along with tips on how the article can be improved in terms of structure, grammar, and word placement, making it a handy tool to get subject lines right.

Screenshot of Email Subject Line Tester Tools - Headline Analyzer

What the tool does: Analyzes headlines

How to test: Enter your subject line, and fill in the sign-up form to get your results

Price: FREE


Well, now you know what we know. Isn’t technology just splendid? A tool to test this, an app to improve that. Hope you use these tools to create attention-capturing subject lines for your cold emails. And do let us know about your experience in the comments below. To conclude, we’d like to leave you with a few ground rules you should keep in mind when writing subject lines:

  • Don’t make promises you can’t keep
  • Don’t write something solely to get their attention
  • Don’t talk about something in the subject line and then write something else inside the email
  • Shed the formality
  • In pursuit of being clever, don’t be vague

That’s all folks.

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