Craft subject lines with confidence! Our free tester checks your subject line against best practices to spot weak spots and help you create emails that get opened. Enter your subject line in the box below to see how it stacks up.
Are you Shakespeare? Because thou hast conquered the inbox.
What data did we consider when building our subject line tester
Here’s a look at the best practices we considered when building our subject line builder, as well as the data that backs it up. Our subject line tester assesses your subject line based on:
Length
Mobile devices show the first 30 characters of a subject line. You can go longer if necessary, but try to keep the main message in the first 30 characters so everyone can see it
Reading level
The Flesch-Kincaid readability test measures how easy text is to read. Since people often scan their inbox, subject lines should be easy to read
Helpful words
Our subject line research identified keywords that correlate with higher opens. We’ll tell you if your subject line includes them
Negative words
Our subject line research identified keywords that correlate with higher opens. We’ll let you know if your subject line includes them
Capitalization
All-caps subject lines are a big no-no since they may be flagged by spam filters. Some audiences may also react better to either sentence case or mixed case subject lines. Test yours to find out
Numbers
Our research shows that using numbers in subject lines can improve open rates
Emojis
Our research shows that using emojis in subject lines improves open rates in some industries by up to 6.4%
Questions
Research shows that subject lines with question marks get higher than average opens
Personalization
Using personalization in a subject line can help it stand out in the inbox
Need subject line inspiration? Get 500+ free examples
Get endless subject line inspiration with our subject line swipe file. It contains over 500 example subject lines from successful campaigns.
You’ll access proven subject lines for welcome emails, surveys, abandoned carts and more. Plus we cover 7 different industries and 12 months' worth of special occasions.
How our email subject line checker works
Our subject line tester checks whether your subject line uses best practices that are thought to improve open rates. We give you an overall score and break down the analysis so you can see exactly where you stand out and can improve.
FAQs about email subject line optimization
What is an email subject line tester?
An email subject line tester is a tool that analyzes your subject line to predict its effectiveness. It does this by showing which best practices your subject line uses and which it ignores.
How will this help my email marketing?
More effective subject lines boost open rates. An increase in open rates will typically lead to an increase in other metrics like click-through rate and orders.
Does the email subject line tester use my data?
The email subject line tester doesn’t use any data beyond the subject line you input into the tester. We delete the subject line data immediately.
What about adding emojis to your email subject lines?
Adding emojis to your email subject can be an effective way to boost your email open rate. However, the ultimate impact depends on your industry and audience. Find out more about how emojis impact open rate here.
What is subject line A/B testing?
Subject line A/B testing is when you compare the performance of two different subject lines for the same email.
Typically, you’ll send each email to a small percentage of your subject, track which one gets the most opens, and then send the winner to the rest of your list to maximize campaign opens.
You can also send each version of the email to 50% of your list and then use the results to guide your future campaigns. This method is useful if you have a list that is too small to get reliable data when sending to a percentage of it, or if you want to send your email at a specific time.
Is this subject line tester free to use?
Yes, the email subject line tester is completely free to use.