Email Subject Line Tester
Check your subject line and preheader against simple guidelines: length, mobile cut-off, capitals, punctuation, emojis, personalization and common spam-trigger phrases. Your text stays in your browser.
Desktop inbox preview
Mobile preview
Previews are approximate. Many phone inboxes show about 40 characters of the subject; the exact cut-off depends on the app, the screen and the font.
Type a subject line to see its score and checklist.
How the Score Works
The score adds up points from the rules below. They are guidelines, not predictions of your open rate: test subject lines with your own list.
- Length (20 points): 20 to 50 characters gets 20; 10 to 60 gets 10.
- Words (5 points): 3 to 9 words.
- No ALL-CAPS words (15 points). Common acronyms such as SEO or ROI are allowed.
- Exclamation marks (15 points): none gets 15, one gets 10.
- Question marks (5 points): one at most.
- Spam-trigger phrases (20 points): none gets 20, one gets 5.
- Personalization token such as {first_name} or *|FNAME|* (10 points).
- Emojis (5 points): one at most.
- Preheader text that differs from the subject (5 points).
Subject Line Questions, Answered
What is a good length for an email subject line?
There is no single right length. A common guideline is about 20 to 50 characters, because many phone inboxes cut the subject at roughly 40 characters. Whatever the length, put the most important words first so they are seen even if the end is cut off.
Should I use emojis in subject lines?
One emoji can help a subject stand out, but it can also look out of place for some brands and audiences, and emojis do not show the same way in every inbox. This tool flags more than one emoji as a guideline. Test with your own list before you rely on them.
Do spam words really send emails to spam?
Modern spam filters look at many signals, such as sender reputation, authentication (SPF, DKIM, DMARC) and how readers engage, not just the words in the subject. A single phrase rarely decides it, but pushy wording, all capitals and lots of exclamation marks can add up and can put readers off. The phrase list here is a guideline, not a list of banned words.
What is preheader text?
Preheader text is the short preview line many inboxes show next to or below the subject. If you do not set it, the inbox usually shows the first text in your email, which may be a 'view in browser' link. Use it to add to the subject rather than repeat it.
How should I A/B test subject lines?
Change one thing at a time, such as length, a question versus a statement, or personalization, and send each version to a random part of your list at the same time. Use a test group big enough to give a clear result, and judge the winner on the goal you care about, such as clicks or sales, not opens alone, since some mail apps report opens unreliably.
Want Emails People Open and Act On?
TML plans, writes and tests email campaigns, from subject lines to the offer and the follow-up.