subject-line-lab

# Subject Line Lab Generates a labeled subject-line + preheader variant set and **heuristically pre-scores** each variant — spam-trigger flags, desktop + mobile length/truncation, emoji count, and the rendered inbox preview (from-name + subject + preheader) — so weak candidates are cut *before* they burn a test cell. This is the pre-test bench for the SEND **E (Engagement)** lever: it sharpens the subject/preheader unit that `email-creative-builder` drafts and hands the ranked survivors, each with a stable variant id, to `send-experiment-designer`. **Scope guard**: this skill drafts and pre-scores subject + preheader variants only. It does not write the body copy or CTA ([email-creative-builder](../email-creative-builder/SKILL.md)), design the A/B / send-time test or read out significance ([send-experiment-designer](../../deliver/send-experiment-designer/SKILL.md)), run the full deliverability spam-content scan ([deliverability-qa](../../setup/deliverability-qa/SKILL.md)), or compute any SEND dimension score. The heuristic pre-score is a **flag, never a verdict**: [email-quality-auditor](../../deliver/email-quality-auditor/SKILL.md) owns the goal-weighted EQS and all four vetoes (S1/S2/N1/D1). ## Quick Start ``` Pre-score these 6 subject lines for truncation + spam triggers, from-name [Sender], promo mode: [paste] ``` ``` Generate 5 subject-line variants + preheaders for [offer], cold-outbound mode, and rank them by pre-score ``` ``` Show the inbox preview (from-name + ...