Email Subject Line Tester

Check a subject line's length, spam-trigger words, all caps and emoji use before you send a campaign.

Preview text (optional)

Characters: 41
Bytes (UTF-8): 41
Words: 7
Preview characters: –

41 characters: fits most inboxes fully
No emoji
No all-caps words
No exclamation marks
No common spam-trigger words found
No personalization tokenA first-name token (like {{first_name}}) often lifts open rates. Optional, not required.

What the checks cover

The tool runs your subject line against the checks email marketers watch most: length against common inbox widths, spam-trigger words, all-caps words, exclamation marks, emoji, and whether you've used a personalization token.

Length	What typically happens
Up to about 41 characters	Usually shows in full, desktop and mobile
42–60 characters	Fits most desktop inboxes; mobile often truncates
Over 60 characters	Commonly cut off in most inboxes

These are general figures based on common inbox widths, not a published spec from any one inbox provider, since exact truncation depends on device, font and screen size.

Using the checks

Front-load the important words. If it truncates on mobile, the first 30 or so characters are what a reader actually sees.
Spam-trigger words are a signal, not a verdict. One flagged word rarely sinks deliverability on its own; several together, especially with ALL CAPS or multiple exclamation marks, add up.
Use the preview text field to check it doesn't just repeat the subject line. It's prime space for a second idea, since most inboxes show both together.

Questions people ask

How long should an email subject line be?

Around 41 characters or fewer keeps it fully visible in most inboxes, desktop and mobile. Longer lines aren't wrong, just more likely to truncate before the interesting part.

Do spam-trigger words actually cause emails to go to spam?

They're one signal among many that spam filters weigh, alongside sender reputation, authentication (SPF, DKIM, DMARC) and engagement history. A single flagged word rarely matters much on its own.

Should I use emoji in subject lines?

They can help a subject line stand out, but some inboxes render them as a blank box, and using them in every campaign dulls the effect. Test with your own list rather than assuming either way.

What's preview text (the preheader)?

The line of text an inbox shows after the subject, pulled from the start of the email unless you set it explicitly. Most email platforms let you set it separately from the subject and body.

Last reviewed 30 September 2026.