8 Email Subject Line Testers to Elevate Your Open Rates

ByMohamed Natheem


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Are you sending valuable emails to your audience but don’t get the engagement and open rates you deserve?

Your subject line may be to blame.

An average person receives around 121 emails every day. If you want to be noticed, you have to stand out. Writing a great subject line is one of the ways to do that.

In this article, you will know the best free email subject line testers you can use to improve your email open rates.

Table of contents

What is an email subject line tester?

Email subject line grader is a tool that helps you optimize your email subject lines to ensure your emails are opened. Such software contain predefined criteria to analyze and improve your subject lines, which are:

  • Emotional sentiment: This feature tells you whether your subject line feels positive or negative. It essentially shows you how emotional your subject line is.

  • Spam words: Subject line testers tell you if you’ve unknowingly used spam words. Often, spammers use spam words to boost open rates.

  • Length: Since user inboxes have limited width, you should not make your subject line too long or short. Email subject line testers will tell you if it is too short or long.

So these are a few properties you can optimize with subject line testers. You will also see many other features unique to different tools. So let’s explore the best email subject line testers and what they offer.

Free email subject line testers you can try now

1. Send Check It

Send Check It compares your subject line with 100,000+ other emails sent by marketers. So it has enough data to tell you what works and doesn't.

Send Check It - email subject line test score

The tool grades your email subject line and provides a few suggestions that help you improve further.

Scannability: Gives you a measure of how easy it is to read your subject line.

Send Check It - email subject line scannability score

Reading grade level: This feature tells the subject line's reading grade level.

Send Check It - email subject line readability grade

Length: Tells you if your subject line has an optimal length and how to improve it if it doesn't.

Send Check It - email subject line length test

Preview: This lets you see a preview of your subject line on different devices.

Sentiment analysis: Tells you if your subject line sounds positive, negative, or neutral.

Send Check It - email subject line sentiment analysis

Spammy words: This shows if your subject line contains popular spam words.

Send Check It - email subject line spam test

Others such as the use of symbols, all-caps, emojis, personalization, and more.

Send Check It is free to use, and you can check as many subject lines as you need.

2. CoSchedule

CoSchedule - Email subject line score

CoSchedule is a visually pleasing subject line tester. It uses a variety of graphics to rate your subject line and suggests ways to improve them.

Words that increase opens: As the name suggests, it shows you if you’re using words that decrease opens.

Words that decrease opens: This shows you if you’re using words, the increase opens so that you can use them in future subject lines as well.

CoSchedule - Email subject line tester

Case: Tell you which case your subject line is in and whether it can get good open rates.

Preview: This shows how your subject line will look on computers and smartphones.

CoSchedule - Email subject line preview

Counts: You can also see your current character, word, and emoji count. It will also show you the optimal count to improve your current one.

CoSchedule - email subject line tests character count

CoSchedule’s subject line tester is free, but you must sign up with your company profile before using the tool.

Write winning subject lines with our free ebook

Proven subject line framework to get higher opens

3. Email Subject Line Grader

Email Subject Line Grader has a few special quirks, like telling you your subject line's type. Here are a few notable features of the tool:

Subject line type: This tells you whether your subject line sounds too generic. And it'll suggest different formats to help your emails stand out.

Email Subject Line Grader shows subject line type

Counts: This will show you your current character and word counts and what is the optimal length so you can optimize.

Word mixture and balance: This will score the sentimental value of words in your email subject line.

Sentimental value of words

This tool is free to use and pretty basic. But features like subject type are a strong reason to try this tool.

4. Omnisend

Omnisend email subject line tester is a simple tool that’ll show you just enough data to get the job done.

Ratings: This will rate your subject line from 0 to 100% to show where your subject line currently stands.

Omnisend rates email subject line

Length: This shows your current character and word length and what are the optimal industry lengths.

Omnisend tests email subject line length

Wording: This tells if your subject line contains helpful and negative words. It will also highlight them so you can use other words instead.

Omnisend tests the usage of words in your email subject line

Scannability: This will analyze capitalization and numbers in your subject line and recommend optimizing those factors and improving the overall email design.

Omnisend tests the readability of your email subject line

This tool is free to use, and no sign-up is required before usage.

5. Moosend's subject line tester

Moosend's email subject line tester

Moosend subject line tester differs from competitors due to its industry and subscribers categorization.

Categorization: Select your industry and subscribers count to niche down your results.

Personalization: Tells if your subject line lacks personalization and what to do next.

And other relevant suggestions.

Recommendations from Moosend's email subject line tester

It is free to use, and you can test as many subject lines as you need.

6. Mailmeteor

Mailmeteor's subject line testing tool scores your email subject line as like any other tool but what makes it unique is its use of GPT-3.

Subject line tester and generator from Mailmeteor

GPT-3 suggestions: Mailmeteor comes with a subject line generator powered by GPT-3 that accepts the subject line and gives better alternate suggestions.

It is free to use, and no login is required.

7. Grademyemail by Netcore

Netcore's subject line tester

Grademyemail is another AI subject line generator and grading tool. It helps create and test email subject lines. You can get all the details about your subject line as you get from any other tool. The only drawback of this tool is that it currently works well for ecommerce brands.

8. TestSubject by Zurb

TestSubject by Zurb

TestSubject is a simple tool that lets you preview your name, subject line, and preheader text on different platforms. This tool aims to help avoid embarrassing situations caused by incomplete subject line rendering. So go ahead and use this tool if you want your subject line to communicate its intended message.

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The best way to deal with a disaster is by avoiding it. So, use the email subject line testers mentioned in this guide to improve your email clicks and open rates.

However, writing great subject lines isn't the only way to improve open rates. You can tell your users to whitelist your email or use a recognizable brand name. Check out our guide on open rates and click-through rates to find out more such tips.

What you should do next

Hey there, thanks for reading till the end. Here are 3 ways we can help you grow your business:

  1. Talk to an email expert. Need someone to take your email marketing to the next level? Mailmodo’s experts are here for you. Schedule a 30-minute email consultation. Don’t worry, it’s on the house. Book a meet here.
  2. Send emails that bring higher conversions. Mailmodo is an ESP that helps you to create and send app-like interactive emails with forms, carts, calendars, games, and other widgets for higher conversions. Get started for free.
  3. Get smarter with our email resources. Explore all our knowledge base here and learn about email marketing, marketing strategies, best practices, growth hacks, case studies, templates, and more. Access guides here.

What should you do next?

Thanks for reading till the end. Here are 3 ways we can help you grow your business:


Get smarter with our email resources

Explore our email marketing guides, ebooks and other resources to master email marketing.


Do better email marketing with Mailmodo

Send app-like interactive emails with forms, carts, calendars, games, etc. to boost email ROI.


Talk to an email expert

Get a 30-min. free email consultation with a Mailmodo expert to optimize your email marketing.

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