What this subject line tester checks
The subject line is the highest-leverage sentence in any email — it decides whether the rest gets read. This tester scores your draft against the factors that measurably affect opens and deliverability: character length versus mobile display limits, a dictionary of common spam trigger phrases, all-caps ratio, exclamation-mark density, and positive patterns like numbers and questions. The score updates on every keystroke, so you can iterate in seconds instead of waiting for campaign stats.
Each finding explains itself. Rather than a bare number, you see exactly which element helped or hurt, and what to change.
How to test a subject line
- Type or paste your subject line into the field.
- Read the score and the individual findings beneath the meter.
- Edit and watch the score respond until the major issues clear.
- Test 2–3 strong variants and A/B them in your email platform.
Patterns that consistently perform
High-performing subject lines tend to share traits: they are specific (“3 changes to your March invoice” beats “Important update”), they front-load the key words so truncation does not kill the meaning, and they match the email body — trust compounds across sends. Once the subject passes, run the body copy through the Email Spam Checker before you hit send.