Email subject line tester

The six things this tester scores

Your subject line starts at 100 and loses points for each pattern that makes a cold email look like a broadcast. Character length is checked first: anything over sixty characters takes the single largest deduction, because that is roughly where mobile clients stop showing the line, and anything under twelve characters takes a small one for being too vague to earn a click.

Word count is scored separately from character count, because a short line can still be a long sentence. Ten words or more is penalised; three to seven is the shape that reads like a note from a colleague. Salesy vocabulary is the heaviest penalty of all when it stacks — free, guarantee, act now, limited time, urgent, discount and their neighbours each add to it.

The last three checks are formatting and intent: ALL-CAPS words, exclamation marks or doubled punctuation, and whether a merge token such as a company or first-name placeholder is present. A line that is entirely lowercase and free of sales words earns an explicit note, because lowercase reads as typed-by-a-human rather than assembled by a tool.

Turning the number into an edit

The panel lists every deduction with the fix attached, so work the list top-down — the heaviest penalty is almost always the fastest win. Re-score after each change; the line usually crosses into the clean band after one or two edits rather than a rewrite.

80 and above

Send it. The line is short, specific, unpunctuated and free of sales vocabulary. Spend your remaining effort on the first sentence of the body instead.

55 to 79

One structural problem, usually length or a single salesy word. Cut the line to under fifty characters or swap the offending word and re-score.

Below 55

Several penalties are compounding — typically a long line that also shouts or promises. Start again from the one thing you know about this specific recipient and write six words.

Why open rate is the weakest metric you have

Open tracking works by loading a pixel, and mail clients now pre-fetch or block images on the recipient's behalf. That means opens are inflated by machines that never read anything and suppressed by privacy settings on people who did. A subject line that lifts your reported open rate has not necessarily reached one extra human.

So use this score the way it is intended: as a check that the line is not actively working against you. Judge the campaign on replies and booked meetings, which no proxy can fake, and treat a strong subject as the thing that buys you the chance to be judged on those at all.

A subject line only works once the mail arrives

None of this applies to a message sitting in a spam folder, and the subject is a small part of that decision. Authentication records, mailbox warmup, per-mailbox daily volume and list hygiene decide placement long before wording does. If your lines score well and opens are still flat, audit the sending setup with the deliverability checker and publish the records the SPF, DKIM and DMARC generator produces before changing another word.