AI Persuasive Email Writer
ILoveDotNet/ilovedotnet
Craft persuasive, goal-driven emails using AI. An agent skill from ILoveDotNet/ilovedotnet.
Generate, evaluate, and A/B test email subject lines for maximum open rates.
Install Email Subject Lines
$ npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install OpenClaudia/openclaudia-skills email-subject-lines --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/OpenClaudia/openclaudia-skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/email-subject-lines .claude/skills/email-subject-lines && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "email-subject-lines" agent skill from https://github.com/OpenClaudia/openclaudia-skills/tree/main/skills/email-subject-lines into .claude/skills/email-subject-lines/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "email-subject-lines", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/OpenClaudia/openclaudia-skills/tree/main/skills/email-subject-linesType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install OpenClaudia/openclaudia-skills email-subject-lines --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/OpenClaudia/openclaudia-skills.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/email-subject-lines .agents/skills/email-subject-lines && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "email-subject-lines" agent skill from https://github.com/OpenClaudia/openclaudia-skills/tree/main/skills/email-subject-lines into .agents/skills/email-subject-lines/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "email-subject-lines", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install OpenClaudia/openclaudia-skills email-subject-lines --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/OpenClaudia/openclaudia-skills.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/email-subject-lines .cursor/skills/email-subject-lines && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "email-subject-lines" agent skill from https://github.com/OpenClaudia/openclaudia-skills/tree/main/skills/email-subject-lines into .cursor/skills/email-subject-lines/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "email-subject-lines", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/OpenClaudia/openclaudia-skills.git --path skills/email-subject-lines--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install OpenClaudia/openclaudia-skills email-subject-lines --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/OpenClaudia/openclaudia-skills.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/email-subject-lines .gemini/skills/email-subject-lines && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "email-subject-lines" agent skill from https://github.com/OpenClaudia/openclaudia-skills/tree/main/skills/email-subject-lines into .gemini/skills/email-subject-lines/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "email-subject-lines", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install OpenClaudia/openclaudia-skills email-subject-linesInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/OpenClaudia/openclaudia-skills.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/email-subject-lines .github/skills/email-subject-lines && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "email-subject-lines" agent skill from https://github.com/OpenClaudia/openclaudia-skills/tree/main/skills/email-subject-lines into .github/skills/email-subject-lines/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "email-subject-lines", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install OpenClaudia/openclaudia-skills email-subject-lines --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/OpenClaudia/openclaudia-skills.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/email-subject-lines .opencode/skills/email-subject-lines && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "email-subject-lines" agent skill from https://github.com/OpenClaudia/openclaudia-skills/tree/main/skills/email-subject-lines into .opencode/skills/email-subject-lines/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "email-subject-lines", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
email-subject-lines- GitHub stars
- 713
- Token cost
- ~3.3k tokens
- SKILL.md length
- 1,544 words
- Files
- 1
- Skills in repo
- 74
- Repo updated
- First seen
- Licence
- MIT
At a glance
Generate, evaluate, and A/B test email subject lines for maximum open rates.
- Works in 11 steps: Curiosity Gap → Urgency → Personalization → …
- Phrases: email subject line
- SKILL.md covers Gathering Requirements, Character Length Optimization, Subject Line Formulas and Preview Text Pairing, plus 4 more sections
- Calls curl; reaches api.resend.com; needs RESEND_API_KEY
What it does
Email Subject Lines is an agent skill from OpenClaudia/openclaudia-skills. Generate, evaluate, and A/B test email subject lines for maximum open rates. Includes formulas for curiosity, urgency, personalization, and more. Trigger phrases: "email subject line", "subject line ideas", "email subject", "write subject lines", "A/B test subject lines", "improve open rates", "email open rate", "subject line formulas".
Its SKILL.md is about 3.3k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.
It sits in Marketing & SEO, covering A/B testing. The repository describes itself as: 77 open-source marketing skills for Claude Code, Codex, and other AI coding agents. SEO, content, email, ads, analytics, and growth. The licence is MIT.
When your agent uses it
- Phrases: email subject line
- Subject line ideas
- Write subject lines
- A/B test subject lines
Example prompts
- “email subject line”
- “subject line ideas”
- “email subject”
- “/email-subject-lines”
Requirements
- A credential in RESEND_API_KEY
Workflow steps
11 steps, taken from the step headings in SKILL.md.
What it can do on your machine
Read from SKILL.md and the folder at commit 28bf209. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
Shell commands in SKILL.md call:
curl
From the folder's file list and the shell code blocks in SKILL.md.
Network
Hosts in commands or code, which the agent is likely to contact:
api.resend.com
Also links to:
resend.com
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names these keys or tokens, usually read from environment variables:
RESEND_API_KEY
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Email Subject Lines loads about 3.3k tokens when it runs. Until then it costs about 90 tokens; SKILL.md has 1,544 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check: notes
The automated check noted patterns worth knowing about, such as sudo or a known installer.
- NoteMentions a .env fileSKILL.md:259
source ~/.claude/.env.global 2>/dev/null - NoteMentions a .env fileSKILL.md:273
source ~/.claude/.env.global 2>/dev/null
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from OpenClaudia/openclaudia-skills at commit 28bf209, republished under its MIT licence (© OpenClaudia). 1,544 words, ~3,254 tokens.
Download SKILL.mdSave it as
.claude/skills/email-subject-lines/SKILL.md (or your agent's skills folder).- name
- email-subject-lines
- description
- Generate, evaluate, and A/B test email subject lines for maximum open rates. Includes formulas for curiosity, urgency, personalization, and more. Trigger phrases: "email subject line", "subject line ideas", "email subject", "write subject lines", "A/B test subject lines", "improve open rates", "email open rate", "subject line formulas".
Email Subject Lines Skill
You are an email subject line specialist. Your job is to generate high-performing subject lines that maximize open rates while maintaining trust and deliverability.
Gathering Requirements
Before generating subject lines, collect these inputs:
- Email purpose - Newsletter, promotional, transactional, nurture, announcement, etc.
- Content summary - What is the email about? (2-3 sentences)
- Audience - Who is receiving this? Segment details.
- Tone - Professional, casual, urgent, playful, mysterious.
- Brand voice - Any specific do's or don'ts?
- Historical data - Past subject lines that performed well or poorly (if available).
- Quantity needed - How many options? (Default: 10 options with 3 recommended A/B pairs)
Character Length Optimization
| Length | Characters | Use For | Why |
|---|---|---|---|
| Short | 20-30 chars | Mobile-first, curiosity-driven | Fully visible on all devices, punchy |
| Medium | 30-50 chars | Most email types (sweet spot) | Enough info without truncation |
| Long | 50-70 chars | Descriptive, B2B, newsletters | More context, but truncated on mobile |
| Very long | 70+ chars | Avoid | Truncated everywhere, looks spammy |
Target: 30-50 characters (6-10 words). This range is fully visible on mobile and desktop.
Mobile preview widths:
- iPhone: ~35-40 characters
- Android: ~33-43 characters
- Gmail app: ~40 characters
Subject Line Formulas
1. Curiosity Gap
Create an information gap that can only be closed by opening the email.
Pattern: Hint at valuable information without revealing it.
| Example | Why It Works |
|---|---|
| "The one metric you're probably ignoring" | Implies they are missing something important |
| "We analyzed 10K emails. Here's what we found." | Teases data without giving the answer |
| "This changed how I think about pricing" | Personal revelation without the detail |
| "The mistake killing your conversion rate" | Specific problem, unnamed solution |
| "I was wrong about cold email" | Contrarian + personal admission |
Rules:
- Do not be vague to the point of irrelevance ("You won't believe this!").
- The email body must deliver on the curiosity promise.
- Use sparingly; overuse trains subscribers to distrust.
2. Urgency
Create time pressure that motivates immediate action.
| Example | Type |
|---|---|
| "Last day: 40% off ends at midnight" | Deadline |
| "Only 12 spots left for the workshop" | Scarcity |
| "Price increases tomorrow" | Price urgency |
| "Your trial expires in 48 hours" | Expiration |
| "Flash sale: 6 hours only" | Time-limited |
Rules:
- Urgency must be real. Fake urgency destroys trust permanently.
- Do not use urgency in every email. Reserve for genuine time-sensitive offers.
- Avoid all-caps urgency words (LAST CHANCE, HURRY).
- Pair with a specific deadline, not vague "soon" language.
3. Personalization
Use subscriber data to make the subject feel individually crafted.
| Example | Data Used |
|---|---|
| "[Name], your weekly marketing digest" | First name |
| "New SEO tips for [Company]" | Company name |
| "Based on your interest in [Topic]..." | Behavioral data |
| "Your [City] marketing event this Thursday" | Location |
| "[Name], you left items in your cart" | Name + behavior |
Rules:
- Personalization boosts open rates by 10-20% on average.
- Do not overuse first names. If every email starts with "[Name]," it loses effect.
- Always set fallback values for empty merge fields ("there" instead of blank).
- Use behavioral personalization (what they clicked/viewed) over demographic when possible.
4. Question
Pose a question the reader wants answered.
| Example | Type |
|---|---|
| "Are you making this SEO mistake?" | Self-diagnosis |
| "What's your content strategy for Q2?" | Planning prompt |
| "Ready to double your email list?" | Aspirational |
| "Which pricing model is right for you?" | Choice |
| "Can you write a landing page in 30 min?" | Challenge |
Rules:
- Questions should be answerable only by opening the email.
- Avoid yes/no questions where the answer is obvious.
- Rhetorical questions ("Want to make more money?") feel spammy.
- The best questions imply a knowledge gap the reader wants to close.
5. Number/Listicle
Include a specific number for concreteness and scannability.
| Example | Why It Works |
|---|---|
| "7 email templates that convert" | Promise of a defined, scannable list |
| "3 things I'd change about my launch" | Small number = quick read |
| "We grew 247% in 90 days" | Specific result = credibility |
| "5-minute fix for your homepage copy" | Number quantifies the effort |
| "11 subject line formulas (steal these)" | Odd numbers outperform even |
Rules:
- Odd numbers (3, 5, 7, 9, 11) tend to outperform even numbers.
- Specific numbers (247%) outperform round numbers (250%).
- Use digits, not words ("7" not "seven") for visual impact in the inbox.
- Keep lists short for emails (3-9 items); save long lists for blog posts.
6. How-To
Promise a practical, actionable skill or outcome.
| Example | Structure |
|---|---|
| "How to write emails that actually get replies" | How to [outcome] |
| "How I got 1K subscribers in 30 days" | How I [result] in [timeframe] |
| "How to fix your bounce rate in 10 minutes" | How to [fix problem] in [time] |
| "How top founders write investor updates" | How [authority] [does thing] |
Rules:
- "How to" subjects set a learning expectation. The email must teach.
- Pair with a specific, measurable outcome when possible.
- Avoid vague how-to's ("How to improve your marketing").
7. Controversy/Contrarian
Challenge a widely held belief to provoke engagement.
| Example | Convention Challenged |
|---|---|
| "Stop writing blog posts" | Content marketing = blog posts |
| "Email marketing is dead (here's what replaced it)" | Channel relevance |
| "Why I stopped A/B testing" | Testing = always good |
| "Your best customers don't read your emails" | Email engagement = loyalty |
| "Forget about SEO for 6 months" | SEO is always important |
Rules:
- You must back up the contrarian claim in the email body.
- Do not be contrarian for shock value alone. Have a genuine insight.
- This formula generates high opens AND high unsubscribes. Use intentionally.
- Works best for thought leadership and newsletter content.
Preview Text Pairing
Every subject line needs a paired preview text. These work together as a unit.
Show full SKILL.md (653 more words)Show less
Pairing Strategies
| Strategy | Subject Line | Preview Text |
|---|---|---|
| Continuation | "We analyzed 10K emails." | "The #1 pattern surprised us." |
| Context | "Big news from our team" | "We're launching something we've worked on for 6 months." |
| Benefit | "Your September marketing plan" | "Templates, calendar, and posting schedule inside." |
| Contrast | "This email has no CTA." | "Just one question I'd love your answer to." |
| Social proof | "The email strategy behind $2M ARR" | "How Acme grew revenue with a 5-email sequence." |
Preview Text Rules
- Keep preview text between 40-90 characters.
- Never repeat the subject line.
- Never leave it blank (ESPs pull body text, which often includes "View in browser").
- Use it to add information the subject line cannot fit.
- End with a complete thought. Truncated preview text looks broken.
A/B Testing Recommendations
What to Test
| Element | Priority | Expected Impact |
|---|---|---|
| Subject line copy | High | 10-30% difference in open rate |
| Personalization vs. no personalization | High | 5-20% lift |
| Emoji vs. no emoji | Medium | 2-10% change (audience-dependent) |
| Preview text variations | Medium | 5-15% impact on open rate |
| Subject length (short vs. medium) | Medium | 5-10% difference |
| Question vs. statement | Low-Medium | 3-8% difference |
| Capitalization style | Low | 1-5% difference |
A/B Test Setup Rules
- Test one variable at a time. If you test subject line AND preview text simultaneously, you cannot attribute the result.
- Minimum sample size: 1,000 per variant for statistical significance.
- Wait time: At least 4 hours before declaring a winner. 24 hours is better.
- Winner threshold: Declare a winner only with 95%+ statistical confidence.
- Document results. Track what won and by how much. Build a subject line playbook.
Recommended First A/B Tests
Run these tests in order to build baseline data:
- Curiosity vs. Direct - "The one thing you're missing" vs. "3 ways to improve your CTR"
- With name vs. Without - "[Name], your weekly tips" vs. "Your weekly marketing tips"
- Short vs. Medium - "New from [Brand]" vs. "[Brand]'s new feature saves 2 hours/week"
- Emoji vs. No emoji - "Your Q2 marketing plan" vs. "Your Q2 marketing plan [calendar emoji]"
Spam Trigger Avoidance
Words and Phrases to Avoid
These trigger spam filters or reduce trust:
High risk: FREE, Act now, Limited time offer, You've been selected, Congratulations, No obligation, Click here, Buy now, Order now, Don't delete, Urgent, Winner
Medium risk: Guarantee, No risk, Double your, Earn $, Discount, Lowest price, One time, Special promotion, Call now, Apply now, Deal
Low risk (use sparingly): Reminder, Exclusive, New, Announcing, Introducing, Sale
Formatting to Avoid
- ALL CAPS in subject line
- Multiple exclamation marks (!!!)
- $$ or other currency symbols in subject
- Re: or Fwd: when not an actual reply/forward
- Excessive emojis (more than 1-2)
- Misleading subject lines that do not match email content
Sending A/B Tests via Resend API (Optional)
If the RESEND_API_KEY environment variable is set, you can send A/B test emails directly from
the CLI using the Resend API. This allows you to test subject line
variants with real recipients and measure actual open rates.
This is entirely optional. The skill works without it and will generate subject lines, preview text, and A/B test recommendations regardless of whether Resend is configured.
Check for Resend API Key
source ~/.claude/.env.global 2>/dev/null
if [ -z "$RESEND_API_KEY" ]; then
echo "RESEND_API_KEY is not set. A/B test emails will not be sent."
else
echo "RESEND_API_KEY is configured. Ready to send A/B test emails."
fiSending an A/B Test (Different Subject Lines, Same Content)
Use the Resend batch endpoint to send the same email body with different subject lines to different segments of your list. Split your recipient list into equal groups:
source ~/.claude/.env.global 2>/dev/null
curl -X POST https://api.resend.com/emails/batch \
-H "Authorization: Bearer ${RESEND_API_KEY}" \
-H "Content-Type: application/json" \
-d '{
"emails": [
{
"from": "Your Name <you@yourdomain.com>",
"to": ["segment-a-recipient1@example.com", "segment-a-recipient2@example.com"],
"subject": "Subject Line Variant A",
"html": "<p>Same email body for both variants</p>"
},
{
"from": "Your Name <you@yourdomain.com>",
"to": ["segment-b-recipient1@example.com", "segment-b-recipient2@example.com"],
"subject": "Subject Line Variant B",
"html": "<p>Same email body for both variants</p>"
}
]
}'Keep the email body identical between variants so that any difference in engagement can be
attributed to the subject line. Track the returned id values to compare open and click
rates in your Resend dashboard.
Output Format
For every subject line request, deliver:
1. Subject Line Options (10-15)
Organized by formula type with character count:
CURIOSITY
1. "The one metric you're probably ignoring" (42 chars)
Preview: "It's not open rate, click rate, or revenue."
2. "We tested 5 CTA buttons. One crushed the rest." (48 chars)
Preview: "The winner increased clicks by 37%."
URGENCY
3. ...2. Top 3 Recommendations
Ranked by predicted open rate with reasoning.
3. A/B Test Pairs
3 recommended A/B pairs with hypothesis for each:
Test 1: Curiosity vs. Direct
A: "The one metric you're probably ignoring"
B: "3 email metrics that predict revenue"
Hypothesis: Curiosity will drive higher opens; direct will drive higher clicks.4. Subject Lines to Avoid
Flag any user-suggested subject lines that are weak, spammy, or misleading, with reasons.
© OpenClaudia, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
Just SKILL.md in skills/email-subject-lines of OpenClaudia/openclaudia-skills.
Open the folder on GitHubat commit 28bf209
Compare with similar skills
Email Subject Lines next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Email Subject Lines this skillOpenClaudia/openclaudia-skills | 713 | — | ~3.3k | Automated safety check: Notes | MIT | |
| AI Persuasive Email WriterILoveDotNet/ilovedotnet | 155 | — | ~3k | Automated safety check: Pass | CC0-1.0 | |
| Ads Copywriterclaude-office-skills/skills | 505 | — | ~2.1k | Automated safety check: Pass | MIT | |
| Memstack Marketing Facebook Adcwinvestments/memstack | 423 | — | ~2.6k | Automated safety check: Pass | Proprietary | |
| Ab Testingcoreyhaines31/marketingskills | 54k | 3 repos | ~3.1k | Automated safety check: Pass | MIT | |
| AnalyticsNexus-JPF/note-companion | 870 | 7 repos | ~2.2k | Automated safety check: Pass | MIT |
Similar skills
Ads Copywriter
claude-office-skills/skills
Multi-platform ad copy generation for Google Ads, Meta/Facebook, TikTok, LinkedIn with A/B testing variants
Memstack Marketing Facebook Ad
cwinvestments/memstack
A skill your agent uses when the user says 'facebook ad', 'FB ad', 'Meta ad', 'Instagram ad', or needs social media ad copy with targeting, creative direction, and A/B test plans for Meta Ads Manager.
Ab Testing
coreyhaines31/marketingskills
When the user wants to plan, design, or implement an A/B test or experiment, or build a growth experimentation program.
Analytics
Nexus-JPF/note-companion
When the user wants to set up, improve, or audit analytics tracking and measurement.
Ad Test Designer
aaron-he-zhu/aaron-marketing-skills
A skill your agent uses when the user asks to "design an A/B test", "set up a creative/landing test", "run an incrementality test", or "is this result statistically and practically material?"…
More from OpenClaudia/openclaudia-skills
All 74 skills in this repoCompetitor Traffic Report
OpenClaudia/openclaudia-skills
Build an interactive competitive-traffic report for any company and its rivals — monthly visits (SimilarWeb), organic search traffic and Domain Rating (Ahrefs) — as one self-contained HTML page with…
Geo Difficulty
OpenClaudia/openclaudia-skills
Score how hard a keyword is to rank for in the AI-search era — page-level URL Rating of real competitors (not just domain DR), Ahrefs keyword difficulty, and whether a given site already ranks or is…
Gsc Portfolio Audit
OpenClaudia/openclaudia-skills
Audit EVERY Google Search Console property at once — rank all sites by clicks and impressions with period-over-period deltas, then diff keywords per site to surface what is newly ranking, rising…
Similarweb Traffic
OpenClaudia/openclaudia-skills
Fetch website traffic estimates (monthly visits, traffic sources, top countries, keywords, engagement, ranks) for any domain from SimilarWeb.
Ahrefs Python
OpenClaudia/openclaudia-skills
Manages Ahrefs API usage in Python using ahrefs-python library.
Ab Test Setup
OpenClaudia/openclaudia-skills
Design, plan, and analyze A/B tests with statistical rigor. An agent skill from OpenClaudia/openclaudia-skills.
Related
Categories
Questions about Email Subject Lines
What does Email Subject Lines do?
Generate, evaluate, and A/B test email subject lines for maximum open rates. Email Subject Lines is an agent skill from OpenClaudia/openclaudia-skills. Generate, evaluate, and A/B test email subject lines for maximum open rates.
When should I use Email Subject Lines?
Email Subject Lines fits situations like: phrases: email subject line; subject line ideas; write subject lines; A/B test subject lines.
How do I install Email Subject Lines in Claude Code?
Run `npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a claude-code`. Or copy the skill folder (skills/email-subject-lines in OpenClaudia/openclaudia-skills) into .claude/skills/email-subject-lines in your project. Claude Code loads it when a task matches its description.
How do I install Email Subject Lines in Codex?
Run `npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a codex`. Or copy the skill folder (skills/email-subject-lines in OpenClaudia/openclaudia-skills) into .agents/skills/email-subject-lines in your project. Codex loads it when a task matches its description.
Can I use Email Subject Lines in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add OpenClaudia/openclaudia-skills --skill email-subject-lines -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/email-subject-lines, .gemini/skills/email-subject-lines, .github/skills/email-subject-lines and .opencode/skills/email-subject-lines in your project.
What does Email Subject Lines need to run?
Going by SKILL.md and its folder, Email Subject Lines needs the command-line tools its instructions call (curl) and credentials named RESEND_API_KEY. Our summary lists: A credential in RESEND_API_KEY.
Does Email Subject Lines access the network?
SKILL.md names 2 domains. In commands or code: api.resend.com; the agent is likely to contact it when it follows the instructions. As links in the text: resend.com. This is read from the text; nothing was executed.
Is Email Subject Lines safe to install?
Our automated static check of SKILL.md found notes only (mentions a .env file), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.
What licence does Email Subject Lines use?
Email Subject Lines is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Email Subject Lines use?
About 3.3k tokens (SKILL.md is roughly 13k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to Email Subject Lines?
Skills that share tags, products or a category with Email Subject Lines: AI Persuasive Email Writer (ILoveDotNet/ilovedotnet, 155 stars), Ads Copywriter (claude-office-skills/skills, 505 stars), Memstack Marketing Facebook Ad (cwinvestments/memstack, 423 stars) and Ab Testing (coreyhaines31/marketingskills, 54k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Email Subject Lines?
OpenClaudia (a GitHub organization) maintains it in OpenClaudia/openclaudia-skills, which has 713 GitHub stars. The repository holds 74 skills in this directory. The repository was last updated on September 18, 2026.
Source: OpenClaudia/openclaudia-skills on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.