Changing The Subject: The Best Free Tools for Email Subject Lines


Changing The Subject: The Best Free Tools for Email Subject Lines

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Kelly Jacobson
May 11, 2022

It’s no secret that email marketing is a key digital strategy for all industries, especially publishing. Everyone is sending email communications and newsletters, but it’s all about standing out from the rest. How do you increase email deliverability? How do you boost open and click-through rates?

If you want your email to be opened, first and foremost you need the best email marketing tools. Digital marketing tools for effective email subject lines are huge time-savers. The subject line is the first thing your recipients see, and it’s what determines if they’ll click to view more.

Mirabel’s Marketing Manager rounds up the top free email marketing tools for the best subject lines. From testing to generating, here are our top picks from around the internet:

Test Subject by Zurb

Test Subject by Zurb is an email subject line tool that tests its appearance on the most popular mobile devices. The goal is to avoid cutting off your subject line at an inopportune place in the copy.

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According to Zurb, “Most people … open an email based on two factors: The sender name and subject line. Mobile … devices often [shorten] subject lines and sender names, leading to sometimes hilarious but frequently disastrous results.”

This digital tool gives you a real-time look at how your sender name, subject line, and preview text will look on certain iPhone and Samsung models. The tool literally changes as you type, making it as instant as it gets.

Spam Check by Postmark

This free email subject line tool tests overall spam score. In a marketing world where email deliverability is key, avoiding the spam folder is Rule No. 1.

Spam Check by Postmark, a transactional email service for web apps, allows you to enter your subject line, preview text, and email message copy to see what may trigger spam filters. It’ll give you recommendations on how to avoid the spam filter, like adding headers.

Email Subject Line Grader by Net Atlantic

As a free digital tool, Email Subject Line Grader determines subject line type, whether it’s generic, how-to, or list. It calculates word and character count, noting:

  • “A subject line of six or seven words is ideal.”
  • “Research has shown that approximately 50 to 65 character length is ideal for email subject lines. However, most subject lines are between 40 and 50 characters.”

This tool also accounts for word mixture and balance, checking for copy with emotion, action, and power to entice recipients to open your email.

This free email subject line checker scores subject lines out of 100. It displays email deliverability and marketing results, adding and subtracting points based on email subject line best practices.

For example, The Newspaper Manager sent an email to remind virtual trade show attendees that our booth is open for business. Our subject line was: Join Us on Oct. 1 for the NNA Virtual Convention and Trade Show. Here’s how we did:

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It also gives you recommendations on how to create better email subject lines. For our example, it said, “Good job! Your subject line is close to meeting all industry standards.”

Email Subject Line Tester by CoSchedule

Complementing the popular Headline Analyzer by CoSchedule, a copywriting tool used for content marketing, is the Email Subject Line Tester. For “creating click-worthy subject lines,” this free email marketing tool also scores your subject line out of 100.

It calculates Words That Increase Opens, recommending at least three from their tried-and-true Word Bank. It also notifies you if you have Words That Decrease Opens, giving you another Word Bank of limiting writing opportunities.

The Email Subject Line Tester considers capitalization (Case) and the use of numbers (Numbers Present), suggesting capital letters and at least one number are email subject line best practices. It even takes into account word, character, and emoji count and shows you mobile and desktop previews.

Mizy by Automizy

Mizy’s free email subject line tester is top-tier. Why? This free email marketing tool doesn’t use old case studies, fake best practices, or company benchmarks.

Mizy is an artificial intelligence that continuously analyzes thousands of real email marketing campaigns. “She” determines email subject line best practices based on feedback from actual campaigns, noting what does and doesn’t work based on open and click-through rates.

According to their website, “Mizy utilizes deep learning to analyze tons of email campaigns and make predictions for you.”

“Based on this information, Mizy’s neurons restructure themselves from time to time as new data is arriving. So the model she uses is continuously changing and developing. She is continuously improving her ‘brain’ and always learning more and more.”

Scoring your subject line out of 100, Mizy gives you recommendations on how to improve your email subject lines based on real data.

Send Check It

This free email marketing tool compares your subject line “to 100,000+ other emails sent by marketers like you.”

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Send Check It gives you an overall letter grade (A to F) for your subject line and breaks it down:

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  • Scannability: “A measure of how easy-breezy it is to read your subject line.”
  • Reading Grade Level: “Reading Grade Level is a mixture of word choice, complexity and length. Writing at a lower level tends to generate more opens.”
  • Word and Character Count
  • Desktop and Mobile Previews
  • Sentiment Analysis: How your subject line makes recipients feel between positive, negative, and neutral
  • Reply or Forward Abbreviations: “Putting a fake RE: or FWD: at the beginning of your subject [line] … is not recommended unless you’re actually responding to an email. Many … anti-spam systems have [flagged] these as suspicious.”
  • Spammy Words: The word “free” is overused in email subject lines, and oftentimes it triggers spam filters. This free tool determines if any potential spammy words are found.
  • Tab Placement: Gmail offers the Primary, Social, and Promotions tabs. Words that incite a sense of urgency often push your email from the Primary to the Promotions tab, decreasing open and click-through rates. Exclamation points, too much capitalization, too many lowercase letters, and excessive punctuation can also push you into the Promotions tab.
  • Personalization: Personalizing your subject line with a first name, industry, title, interest, or geographic information can boost open rates.
  • Emojis: According to their website, “2.5% of [subject lines] contain an emoji,” as an eye-catcher.
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These images from Send Check It demonstrate how well our subject line (Join Us on Oct. 1 for the NNA Virtual Convention and Trade Show) did.

The Omnisend Email Subject Line Tester

Boost your open rates with the Omnisend Email Subject Line Tester. This free email marketing tool grades your subject line out of 100%. It considers word and character count; helpful and negative words (with a link to a list of words to increase open rates); spam folder alerts, including spammy words and characters, as well as excessive punctuation; scannability; and mobile and desktop previews.


Pivoting away from subject line checkers is ActiveCampaign’s free email subject line generator. Its process is simple: “Choose a keyword category (Benefit, Topic, or Pain-Point), then enter your keyword. Click ‘generate subject lines’ to get a list of ideas for your next great subject line!”

If you’d prefer different options, hit “Generate more suggestions.” This digital tool combines keyword research and email marketing to create a customizable shortcut for your next campaign — no surprise for a multifunctional automation software, like Mirabel’s Marketing Manager, that combines email marketing and CRM.

If you’re looking to test email subject lines, plenty of free digital marketing tools can help. Test, check the results, and repeat. It’s an effective yet simple strategy to boost open rates and email deliverability.

For more information about the basics of email marketing, download the free white paper from Mirabel’s Marketing Manager.


Watch an overview to learn how B2B marketing automation by Mirabel Technologies can help you increase traffic, optimize your funnel, drive more leads, improve conversions, and boost ROI — at a price you can afford!

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