Preview how a subject line and preheader may truncate on mobile or desktop, check length and punctuation, and get practical editing prompts. This is a transparent writing heuristic — not a deliverability or spam-filter guarantee.
The score rewards clear, mobile-friendly length and flags patterns that can look shouty or promotional. It cannot predict opens, inbox placement or individual audience preferences. Test a few honest variants with your own subscribers, then keep the version that earns engagement without misleading anyone.