Stable Digital

Email Subject Line Tester

Paste your subject line and get an instant score based on length, spam-trigger words, personalisation, and urgency.

What this tool does

Scores a subject line before you send it — length, clarity, spam triggers, and open-rate signals. Paste a subject line in; get a score and specific fixes out.

How to use it

Bring the subject line of your next campaign, or your last one. Test a couple of variants against each other — the comparison is usually more revealing than any single score.

Why this matters

The subject line decides whether the rest of your email exists at all. A weak one can halve your open rate, which halves everything downstream — clicks, bookings, sales — for the same effort and cost.

How we close this gap

Our Email Marketing product writes, tests and sends your campaigns for you, with every send measured and the next one improved by it.