Email Subject Line Tester

The subject line does two jobs before your email earns a single read: it must get past spam filters, and it must win the open in a crowded inbox. This tester scores both dimensions at once, checking the measurable traits that correlate with strong open rates and flagging the ones that correlate with the junk folder — all recalculated live as you type, so you can iterate on drafts in seconds.

The checks, and why they matter: length of 30–50 characters earns the largest share of the score, because that range displays fully on both desktop and mobile clients (phones often cut at 35–40, so front-load the hook). Three to nine words keeps the promise scannable. Spam trigger phrases — 'act now', 'buy now', 'click here', 'limited time', 'winner', 'guarantee', '100%' and their kin — are counted because filters and, worse, trained human reflexes treat them as noise. ALL-CAPS words read as shouting and are a classic filter signal. Personalization — a simple 'you' or 'your' — reliably lifts opens by making the line about the reader rather than the sender. And emoji are counted with a light touch: one can add warmth and stand out in a text-only inbox; a row of them looks like spam.

The score compares drafts, not destinies — deliverability also rides on your sender reputation, list hygiene and email content. Use the tester to shortlist two or three strong candidates, then let an A/B test on a slice of your real list pick the winner. Over a year of campaigns, that habit compounds into meaningfully more reach from the same list.