BYTETOOLS

Email Subject Line Checker

Check where your email subject line gets cut off in Gmail, Outlook and iPhone Mail, and see which spam-trigger words, capitals and punctuation could hurt it.

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Characters
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Words
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Pixel width
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Score

Enter a subject line above to see where it truncates and what might trip a spam filter.

The score is a transparent rule-of-thumb built from length, capitalisation, punctuation and a list of commonly cited spam-trigger phrases — no real spam filter is consulted, and no single word gets a message blocked on its own. Your subject line is analysed in your browser and never sent anywhere.

What is the Email Subject Line Checker?

Subject lines fail in two ways: they get cut off, or they read like spam. This checker measures yours in characters, words and rendered pixels, then shows exactly where it truncates in four common inboxes — Gmail on desktop and mobile, Outlook on desktop and iPhone Mail in portrait — with the lost text struck through.

  • Character, word and pixel-width measurement using canvas text metrics
  • Truncation previews for Gmail desktop and mobile, Outlook and iPhone Mail
  • All-caps ratio, repeated punctuation, exclamation and emoji counts
  • Checks against a built-in list of commonly cited spam-trigger phrases
  • Transparent score from 0 to 100 with every issue explained in plain English
  • Highlights engaging words already present, plus a copyable report

How to use the Email Subject Line Checker

  1. 1

    Type or paste the subject line you plan to send.

  2. 2

    Check the character count, word count and rendered pixel width.

  3. 3

    Look at the four inbox previews to see where each client cuts the line off.

  4. 4

    Work through the flagged issues — capitals, punctuation, emoji and spam wording.

  5. 5

    Copy the full report once the score looks right.

About the Email Subject Line Checker

Subject lines fail in two ways: they get cut off, or they read like spam. This checker measures yours in characters, words and rendered pixels, then shows exactly where it truncates in four common inboxes — Gmail on desktop and mobile, Outlook on desktop and iPhone Mail in portrait — with the lost text struck through.

It then works through the deliverability basics: the proportion of capitals, repeated punctuation, exclamation marks, emoji count, stray leading or trailing whitespace, a misleading Re: or Fwd: prefix, and matches against a built-in list of commonly cited spam-trigger phrases. Every finding is written out in plain English rather than hidden behind a grade.

The score from 0 to 100 is a transparent rule of thumb built from those same checks — no real spam filter is consulted, and no single word gets a message blocked on its own. Your subject line is analysed in your browser and never sent anywhere, so unreleased campaigns are safe to paste in.

Frequently asked questions

How long should an email subject line be?

Around 30 to 50 characters is the safe range, because that survives on mobile where most people read first. Gmail on desktop shows roughly 70 characters and Outlook about 60, so anything longer is effectively invisible to a large share of your list.

What words trigger spam filters in a subject line?

Phrases promising free money, urgency or guaranteed results are the classic ones — free gift, act now, risk free, limited time, guaranteed, work from home. This tool flags matches against a list of commonly cited phrases so you can rewrite them.

Why do subject lines get cut off on mobile?

Mobile inbox lists show a single line in a narrow column, so there is only room for about 30 to 35 characters before the text is truncated. Front-load the message so the important words survive that cut on every device.

Do emoji in a subject line hurt open rates?

One well-chosen emoji is usually fine and can help a line stand out, but several together look promotional and may not render identically in every client. The checker counts them and flags a subject line carrying more than two.

Is the score an actual spam-filter result?

No. It is a transparent rule of thumb calculated from length, capitalisation, punctuation, emoji and known trigger phrases, all of which are shown to you. Real filters weigh sender reputation, authentication and body content far more heavily than the subject.

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