8 Email Subject Line Testers to Elevate Your Open Rates

author image

Written by: Mailmodo


Facebook logo
Linkedin logo
Twitter logo
Whatsapp logo
Pinterest logo
mail logo
copy link

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.

If you’re struggling with writing great subject lines, this guide shares the top email subject line testers to help you power through them.

Table of contents

What is an email subject line tester?

Email subject line tester is software that helps you optimize your email subject lines to improve their clickability factor. Such softwares 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 let you know if you’ve used spam words unknowingly. 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 8 best email subject line testers and what they’ve to offer.

Top 8 email subject line testers in 2022

Here are the top 8 email subject line testers (in no particular order):

1. Send Check It

1. Send Check It Homepage

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 what doesn’t. Here are the highlighting features of Send Check It:

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

  • Reading grade level: This feature tells you your reading grade level. If your subject line has a 5th-grade reading level, that means 5th-grade students can understand your subject line.

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

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

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

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

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

2. CoSchedule

2. Co Schedule Homepage

CoSchedule is a visually pleasing subject line tester. It uses many diagrams to rate your subject line and suggests ways to improve them. Here are notable features of CoSchedule:

  • 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.

  • 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.

  • 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’s subject line tester is free to use, but you’ve to sign up with your company profile before using the tool.

3. Email Subject Line Grader

3. Email Subject Line Grader Homepage

Email Subject Line Grader has a few special quirks, like telling you your subject line's “Subject Type.” Here are a few notable features:

  • Subject line type: This tells you whether your subject line sounds too generic. Instead, it’ll suggest different formats that are not used often so you can stand out.

  • 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 show the percentage of emotional words in your subject line.

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

4. Omnisend

4. Omnisend Homepage

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

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

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

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

  • Scannability: This will analyze capitalization and numbers in your subject line and recommend how to optimize those factors and improve the overall email design.

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

5. Moosend subject line tester

5. Moosend subject line tester Homepage

Moosend subject line tester differs from competitors due to its industry and subscribers categorization. Here are the notable features:

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

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

  • Segmentation: Gives you ideas on segmenting your subject line to get high conversions.

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

6. TestSubject

6. TestSubject Homepage

TestSubject lets you preview your name, subject line, and preheader text on different platforms. This tool aims to help avoid cringe-worthy 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.

7. IsNotSpam

7. IsNotSpam Homepage

IsNotSpam is a spam checker that'll check your email content (including subject lines) to predict whether it will trigger spam filters. Chances of genuine emails ending in spam aren't zero since your emails may contain spam trigger words. So use this free tool to identify if your email content is spammy and how to improve it.

8. Subject Line

8. Subject Line Hompeage

As the name suggests, Subject Line is a tool dedicated entirely to testing subject lines. This tool will score your subject line out of 100 points and tell you its rationale. This is a completely free-to-use tool.


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

However, writing great subject lines isn't the only way to improve open and click-through rates. You can tell your users to whitelist your email. Create engaging content so users will be excited to receive them. 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. Sign up now and send 10k free emails/month. Sign up here.
  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.