# Create Test-Ready Email Subject Lines

Weak subject lines can waste email test cells and obscure a useful offer. This skill creates and ranks subject and preheader variants with clear heuristic flags before a campaign test.

## Install

```bash
npx skillstore add aaron-he-zhu/subject-line-lab
```

## Metadata

- Status: approved
- Slug: aaron-he-zhu-subject-line-lab
- Version: 19.0.0
- Author version: 19.0.0
- Skillstore revision: r2
- Version status: valid
- Tree hash: d577458e0d2638f5371defaf8007f92a4925a7e37905dd04fe35495c45a5dd36
- Author: aaron-he-zhu
- GitHub username: aaron-he-zhu
- License: Apache-2.0
- Repository: https://github.com/aaron-he-zhu/aaron-marketing-skills/tree/main/email/engage/subject-line-lab
- Ref: 0715a6e09ea875c8e28cb705ce87cc83045e69c1
- Supported tools: Claude, Codex, Claude Code
- Audit status: complete
- Agent install advisory: allowed
- Manual install advisory: allowed
- Artifact signature: available
- Audit attestation: unavailable
- Human verification: not\_verified
- Risk factors: filesystem, external\_commands, network
- Quality score: 78
- Quality tier: bronze
- Public page: https://skillstore.pages.dev/skills/aaron-he-zhu-subject-line-lab
- Manifest: https://skillstore.pages.dev/api/skills/aaron-he-zhu-subject-line-lab/manifest

## Capabilities

- Generates three to eight subject and preheader variants with stable IDs and angle labels.
- Counts subject and preheader characters for desktop and mobile truncation checks.
- Flags common subject-level spam patterns, including all-caps runs and deceptive prefixes.
- Counts emojis and applies different guidance for promotional and cold-outbound emails.
- Renders from-name, subject, and preheader as an estimated inbox preview.
- Ranks variants and explains which candidates should advance to testing.

## Use Cases

- Prepare a promotion test: Create and rank subject and preheader options before a promotional campaign test.
- Review cold outreach: Check B2B outreach subjects for truncation, emoji use, and misleading patterns.
- Improve a newsletter launch: Compare newsletter subject options and preview the recipient inbox view.

## Prompt Templates

### Check one subject line

```
Pre-score this subject line and preheader for a newsletter: [subject] / [preheader]. From-name: [name].
```

### Generate promotion options

```
Generate five subject-line and preheader variants for [offer] in promo mode. Use from-name [name] and rank them by heuristic pre-score.
```

### Review candidate list

```
Pre-score these six subject lines for desktop and mobile truncation, spam patterns, emoji count, and inbox preview. Mode: [promo or cold]. From-name: [name]. Candidates: [list].
```

### Create a test-ready shortlist

```
Generate eight distinct subject and preheader variants for [offer]. Use [promo, cold, or newsletter] mode. Mark measured and estimated checks, cut weak options, and provide a ranked shortlist for an A/B test.
```

## Limitations

- It provides heuristic flags, not mailbox-provider inbox-placement decisions.
- It does not write email body copy, CTAs, or complete deliverability audits.
- It cannot validate claims, prices, discounts, or scarcity without user-provided evidence.
- Inbox rendering varies by email client, device, and recipient settings.

## Best Practices

- Provide the offer, audience, mode, and from-name before generating variants.
- Treat spam and truncation results as estimates, then validate with campaign results.
- Use one variable per test cell after selecting the ranked shortlist.

## Anti Patterns

- Do not present a clean heuristic pre-score as an inbox-placement guarantee.
- Do not invent discounts, statistics, scarcity, or personalization claims.
- Do not use this skill as a substitute for body-copy review or full deliverability testing.

## Security Audit

- Audited at: 2026-07-27T11:45:28.008\+00:00
- Summary: All 53 static detections are false positives caused by Markdown code spans and relative documentation links. The skill gives local email-writing guidance, labels heuristics as estimates, treats imported material as untrusted, and requires confirmation before saving memory. No prompt injection, data exfiltration, command execution, or unsafe filesystem behavior was found.

## Stats

- Views: 1
- Downloads: 7
- Favorites: 0
- Popularity score: 0