Free Email Subject Line Tester
Check length against mobile truncation, spot trigger phrases, and catch the punctuation and capitalisation habits that make a subject line read as promotional.
Runs entirely in your browser. Nothing you type is sent to us or stored.
Type a subject line to see it scored.
Why subject line length matters
Desktop clients typically show sixty characters or more, but most email is opened on a phone, where the visible portion is often closer to forty. Anything past that is truncated. This does not mean short is always better \u2014 it means the words that carry the meaning should come first, so a truncated subject still says something useful.
The habits worth breaking
Subject lines are weighted more heavily than body copy by filters, so trigger phrases cost more here. Multiple exclamation marks, mostly-capital text, and currency or discount figures all push a subject toward the promotional tab even when the message itself is legitimate.
The one to avoid entirely is opening with \u201cRe:\u201d or \u201cFwd:\u201d on a message that is neither. It is deceptive, it damages trust the moment the recipient opens it, and in many jurisdictions it breaches the rule against misleading subject lines. This tool flags it as a critical issue for that reason.
About this tester.
How subject lines are scored and what the score is worth.
How long should an email subject line be?
Aim for roughly 30 to 50 characters. Desktop clients show more, but most email is read on a phone where the visible portion is often around forty characters. The practical rule is not to be short but to front-load — put the words carrying the meaning first, so a truncated subject still communicates something.
Do emoji in subject lines hurt deliverability?
One emoji is generally fine and can help a subject stand out in a crowded inbox. Several read as promotional and are flagged here for that reason. The bigger risk is mismatch: an emoji that does not fit the message or the audience reduces trust more than it gains attention.
Why is starting with "Re:" flagged as critical?
Because it is deceptive. Prefixing a subject with Re: or Fwd: on a message that is not a reply is an attempt to make a cold message look like an ongoing conversation. It damages trust the instant the recipient opens it, and in many jurisdictions it breaches the rule against misleading subject lines in commercial email.
Should I personalise the subject line?
Usually yes. Merge fields drawn from your own list data generally improve open rates, and they have the side benefit of making messages non-identical across a campaign, which is its own small deliverability gain. The tool recognises merge field syntax and notes it as a positive.
A good subject line still needs to arrive.
Subject lines only matter for messages that reach the inbox. Email.biz.pk handles the authentication, distribution and pacing that get them there.
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