Subject Line Lab includes pricing or quota commentary; at least one code block. At roughly 1,606 words the SKILL.md is on the longer end of the catalog distribution.
Subject Line Lab sits in the Science & Research category under the science-misc sub-topic in the ClaudSkills catalog. There are 10 related skills indexed alongside it; comparing a few before installing usually reveals which fits your workflow best.
These notes are auto-generated from features detected in the SKILL.md file and from this catalog's structure — they aren't part of the source repository.
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.
Subject Line Lab is a community-contributed Claude Code skill in the science-misc sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/subject-line-lab/ and loads when your prompt matches the skill's trigger.
When to invoke it: Use when the user asks to "generate subject line variants", "pre-score my subject lines", or "will this subject get truncated / trigger spam filters"; produces a labeled subject + preheader variant set and a per-variant heuristic pre-score card — spam-trigger flags, length/truncation across desktop + mobile, emoji-count, and the inbox preview render (from-name + subject + preheader) — before any test is run. Not for the body copy or CTA — use email-creative-builder; not for the A/B test design or significance read — use send-experiment-designer; not for the goal-weighted EQS or the S1/S2/N1/D1 vetoes — use email-quality-auditor.
The Subject Line Lab Claude Code skill is built for researchers, data scientists, academics, and analysts working with complex data and scientific literature. It's part of ClaudSkills (also referred to as Claude Skills or Claude Code Skills) — the open community-curated registry of 153,000+ SKILL.md files for Anthropic's Claude Code agent and the wider Claude ecosystem (Claude API, Claude Agent SDK).
mkdir -p ~/.claude/skills/subject-line-lab curl -L https://claudskills.com/skills/subject-line-lab/SKILL.md \ -o ~/.claude/skills/subject-line-lab/SKILL.md
Or just download SKILL.md directly and drop it into ~/.claude/skills/subject-line-lab/. Claude Code auto-discovers it on next session.
Skills live at ~/.claude/skills/subject-line-lab/SKILL.md on macOS/Linux, or %USERPROFILE%\.claude\skills\subject-line-lab\SKILL.md on Windows. See the full install guide for step-by-step instructions.
Open @claudskills_bot on Telegram, tap Open Desktop App, and the desktop app installs this skill for you. Or share the bot link with a colleague — they get the same one-tap install. Learn more →
The ClaudSkills desktop app installs any skill directly into ~/.claude/skills/ with one click — no terminal required. Pro starts at $9/mo or $149 lifetime.
For the full experience including quality scoring and one-click install features for each skill — upgrade to Pro.
SKILL.md from the source repository to ~/.claude/skills/subject-line-lab/SKILL.md and restart Claude Code. Both flows are detailed at claudskills.com/install/.SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. Subject Line Lab is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Science & Research category. Learn more at /learn/what-is-a-claude-skill/.If you reference this skill in a blog post, paper, or documentation, you can cite it as:
@misc{subject-line-lab-2026,
author = {aaron-he-zhu},
title = {Subject Line Lab [Claude Code skill]},
year = {2026},
publisher = {ClaudSkills},
url = {https://claudskills.com/skills/subject-line-lab/}
}Grade A · scanned 2026-07-18 — free static scan against the OWASP Agentic Skills Top 10.
The scan flagged 1 of 10 categories (filesystem), including lower-severity patterns. Patterns shown inside code fences are weighted as examples rather than instructions — read the grading methodology for what this does and does not guarantee.
Browse all Science & Research skills in the ClaudSkills registry, or explore these other picks from the same category:
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SKILL.md files, not affiliated with, endorsed by, or sponsored by Anthropic.