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Toolkit · Subject Line Analyzer

Score your subject line — and see how it'll look in inbox.

Scoring across 7+ heuristics. Real inbox-preview mockups for Gmail desktop, Apple Mail mobile, and Outlook dark mode. Mobile-truncation visualizer. Auto-generated rewrite suggestions for the issues we flag.

Enter a subject line above

You'll see scoring on the left and inbox preview mockups on the right — exactly how recipients will see it across Gmail, Apple Mail, and Outlook.

Compare two subject lines side-by-side. We'll score both and tell you which is stronger.

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Tools & Platforms We Work With

100% JSS & Top Rated Plus on Upwork — personal founder’s profile + ReplyWorks agency 8+ years running B2B outbound No lock-in, month-to-month