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Cold email subject line checker

The subject line helps decide whether a cold email is opened, and this checker tests yours against the habits that get emails ignored or filtered. It runs in your browser, so nothing you type leaves the page.

Updated November 2026

Type a subject line to check it

    The checker tests nine things in every cold email subject line

    • The length check flags anything over 40 characters, because a phone inbox cuts long subject lines short.
    • The word count check flags lines of more than nine words.
    • The spam word check flags advertising and scam wording such as "free", "guarantee" or "act now".
    • The fake reply check flags a "Re:" or "Fwd:" on a first email, which suggests a conversation that never took place.
    • The capitals and punctuation check counts words in capitals, repeated exclamation marks and emoji against the line.
    • The title case check flags a capital on every word, which reads like an ad.
    • The placeholder check flags a leftover {{company}} or [First name], which tells the reader the email was automated.
    • The money check flags prices and percentages, which can make a subject line look like an ad.
    • The specific to the reader check gives credit to a line that names their business.

    A good cold email subject line reads like a colleague wrote it

    The patterns below suit business-to-business outreach. Each one is an illustrative example to adapt.

    • A question about them works well, as in "Question about [Company]'s [area]".
    • The topic can simply be stated, as in "[Company] and [what you do]".
    • A short observation can be the subject, as in "Your booking page on a phone".
    • The next step suits a follow-up better than a first email, as in "Quick call on Thursday?".

    A short line in lower case, such as "idea for [company]", is perfectly acceptable. It looks like a real email, which is the whole point.

    Some subject lines break the law as well as the reader's trust

    The FTC's CAN-SPAM compliance guide says a subject line must accurately reflect the content of the message, and the law makes no exception for business-to-business email. The examples below fail the reader, and the first fails the rule too.

    • "Re: our conversation" misleads when the two of you have never spoken.
    • "URGENT: last chance to grow your revenue!!!" reads as an ad from its first word.
    • "Partnership Opportunity For Your Business" is vague and written in title case.
    • "Hi {{first_name}}" shows a placeholder that never filled.

    The subject line earns the open, and the first line and the ask earn the reply. The guide to following up on a cold email covers what happens after the first message.

    Questions

    How long should a cold email subject line be?
    The checker treats 40 characters as its target, because a longer line is cut short in many phone inboxes. It also flags lines of more than nine words.
    Should a cold email subject line name their company?
    A subject line that names their company shows the email is about them, and the checker gives credit for it.
    Is it acceptable to start a cold email subject with Re:?
    No. A Re: on a first email suggests an earlier conversation that never happened, and the FTC says a subject line must accurately reflect the content of the message.
    Which words should a cold email subject line avoid?
    The checker flags advertising and scam wording such as free, guarantee, act now, limited time, winner and urgent, along with capitals and repeated exclamation marks.
    Does the subject line affect deliverability?
    The subject line is one part of what a spam filter reads, and a line full of advertising words also puts readers off. The checker flags those words so they can come out.