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Nobody reads a whole subject line. Gmail on a phone shows the first 37 characters, Apple Mail on an iPhone 48, Outlook in the browser about 51. What comes after disappears behind an ellipsis. This subject line tester shows your subject line and preview text as four inboxes show them, and points out what a reader or spam filter notices: capitals, exclamation marks, words that smell of spam, preview text that repeats the subject.
The test runs in your browser. Your text goes to no server and we keep nothing. There is no score, because a good subject line depends on who reads it. You do see what the reader sees, and that is usually enough to make it better.
How many characters each inbox shows
| Inbox | Subject | Preview text | Note |
|---|---|---|---|
| Gmail app on a phone | 37 characters | 39 characters | On an iPhone 14; Android shows a few fewer |
| Apple Mail on an iPhone | 48 characters | 99 characters | Two lines of preview |
| Gmail in the browser | about 88 characters, with the preview | What is left | At a 1400 pixel window |
| Outlook in the browser | about 51 characters | By screen width | At a 1400 pixel window |
Measurements by EmailToolTester. The real limit depends on your device, font size and window width; the tester uses these figures as a guide.
A subject line that works and one that does not
- Length
- WorksThe key point in the first 37 characters
- Does not workA long sentence whose point comes after the cut
- Content
- WorksSays what is in the email
- Does not workPromises something the email does not deliver
- Tone
- WorksA plain sentence, as you would say it to a customer
- Does not workCAPITALS, three exclamation marks, FREE
- Preview
- WorksAdds a second reason to open
- Does not workEmpty, or the first line of your menu
- Tricks
- WorksNone
- Does not workRe: or Fwd: on an email that is no reply
How to use the tester
Type your subject line in the first field and your preview text in the second. The preview text is the short line next to or under the subject; in your newsletter tool it is called the preheader. Leave it empty and the inbox shows the first words of your email, often "View this email in your browser". Under the fields you see four inboxes with your text, and a list of what stands out. Adjust until the key point shows in every inbox.
What the signals mean
Too long means Gmail on a phone cuts your subject. Above 48 characters Apple Mail cuts too. Too short, under 12 characters, often says too little. Capitals across whole words and more than one exclamation mark read as shouting. Words like free, guaranteed or last chance stand out to readers and to some filters. An emoji is fine, but not as the only content. Re: or Fwd: on a newsletter is misleading. And preview text that repeats the subject wastes your second chance.
Why spam words weigh less than they used to
Spam filters today look mainly at who you are and how your readers respond. Gmail asks bulk senders to keep spam complaints under 0.3 percent, and checks whether your domain has SPF, DKIM and DMARC. A word like free will rarely block an email from a good sender. It still stands out to the reader, who decides whether to open or click spam. Email landing in spam? Read why emails go to spam and check your domain with our DMARC checker.
A subject line in five steps
- Say what is insideOne sentence about the content, not about yourself.
- Put the point firstWhat counts sits in the first 37 characters.
- Write the previewA second reason to open, not a repeat.
- Read it aloudDoes it sound like something you would say to a customer?
- Test and sendSend a test to Gmail and Outlook, on phone and laptop.
Subject line examples
| Kind of email | Subject line | Preview text |
|---|---|---|
| Newsletter | Three questions customers asked this month | And the answer that saves you time |
| Invitation | Workshop in Ghent on 12 March | Twenty seats, coffee included |
| Quote follow-up | Your quote for the new website | Two questions to wrap it up |
| Welcome email | Welcome, here is what to expect from us | One email a month, unsubscribe any time |
Each of these fits in 37 characters or puts the point before the cut. None promises anything the email does not do. How to build the rest of your email is in how to write a newsletter. Writing well is a craft: what copywriting is, our glossary explains.
A name or a question in your subject
A first name in the subject line stands out, as long as it is right. A list with empty or wrong names gives "Hi ," or a name in capitals, and that stands out more than you want. Set a fallback value in your tool, such as "Hi there". A question as subject works when the reader really wants the answer, and when the email gives it. Test both versions once on a small part of your list before sending them to everyone; most tools do this with an A/B test.
What the tester does not do
The tester does not predict an open rate. Since Apple Mail's privacy protection, opens are an unreliable number, because Apple loads emails in advance. Look at clicks, replies and unsubscribes instead. The tester also does not read your whole email: whether it lands in spam depends more on your domain, your list and your sending history than on your subject. Where your subject line fits a bigger plan is in email marketing strategy.
Have your newsletter written
Want someone else to write, test and send your subject lines and newsletters? See our email marketing services. Picking a tool first? Read create a newsletter for free or Mailchimp pricing. And if you write on LinkedIn, check your post with our LinkedIn post preview. A question about your own email? Send us a message.
Subject lines, the questions that remain
How long should a subject line be?
There is no hard limit, but Gmail on a phone shows 37 characters and Apple Mail 48. Put the point in the first 37.
What is preview text or a preheader?
The short line next to or under your subject in the inbox. You set it in your newsletter tool.
Can I put an emoji in my subject line?
Yes, if it adds something. An emoji counts as one character and looks a little different in each inbox.
Does the tester keep my text?
No. The test runs in your browser and sends nothing on.