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SKILL.md
npx skills add inference-sh/skills --skill email-design
Email marketing design with layout patterns, subject line formulas, and deliverability rules. Covers welcome sequences, promotional emails, transactional templates, and mobile optimization. Use for: email marketing, newsletter design, drip campaigns, email templates, transactional emails. Triggers: email design, email template, email marketing, newsletter design, email layout, email campaign, drip campaign, welcome email, promotional email, transactional email, email subject line, email header image, email banner
npx skills add inference-sh/skills --skill email-design
Install the belt CLI skill:
npx skills add belt-sh/cli
Design high-converting marketing emails with AI-generated visuals via inference.sh CLI.
Requires inference.sh CLI (
belt). Install instructions
| Constraint | Value | Why |
|---|---|---|
| Max width | 600px | Gmail, Outlook rendering standard |
| Mobile width | 320-414px | Responsive fallback |
| Single column | Preferred | Better mobile rendering |
| Two column | Use sparingly | Breaks on many clients |
| Image width | 600px max, 300px for 2-col | Retina: provide 2x (1200px) |
| Font size (body) | 14-16px | Below 14px is hard to read on mobile |
| Font size (heading) | 22-28px | Must be scannable |
| Line height | 1.5 | Readability on all devices |
The most effective email layout funnels attention to a single CTA:
| Formula | Example | Open Rate Impact |
|---|---|---|
| Number + benefit | "5 ways to cut your build time in half" | High |
| Question | "Are you still deploying on Fridays?" | High |
| How-to | "How to automate your reports in 3 steps" | Medium-High |
| Urgency (genuine) | "Last day: 30% off annual plans" | High (if real) |
| Personalized | "[Name], your weekly report is ready" | Very High |
| Curiosity gap | "The one feature our users can't stop talking about" | Medium-High |
| Rule | Value |
|---|---|
| Length | 30-50 characters (mobile truncates at ~35) |
| Preview text | First 40-100 chars after subject — design this intentionally |
| Emoji | Max 1, at start or end, test with your audience |
| ALL CAPS | Never — triggers spam filters |
| Spam trigger words | Avoid: "free", "act now", "limited time", "click here" in subject |
| Personalization | [First name] in subject lifts open rates 20%+ |
The preview text appears after the subject line in the inbox. Don't waste it.
| Element | Content |
|---|---|
| Subject | "Welcome to [Product] — here's what's next" |
| Header | Brand image or product screenshot |
| Body | 3-4 sentences: what they signed up for, what to expect, one quick win |
| CTA | "Complete your setup" or "Try your first [action]" |
| Timing | Immediately after signup |
| Element | Content |
|---|---|
| Subject | Benefit-focused, urgency if real |
| Header | Hero image showing the offer/outcome |
| Body | Problem → solution → offer → deadline |
| CTA | "Get 30% Off" or "Start Free Trial" |
| Urgency | Real deadline, not fake scarcity |
| Element | Content |
|---|---|
| Subject | "New: [Feature name] is here" |
| Header | Screenshot or visual of the feature |
| Body | What's new, why it matters, how to use it |
| CTA | "Try [feature]" |
| Rule | Why |
|---|---|
| Clear purpose in subject | "Your order #1234 is confirmed" |
| Minimal design | Don't confuse with marketing |
| Key info above the fold | Order number, amount, date |
| No promotional content (mostly) | CAN-SPAM allows some, but keep minimal |
| Rule | Value |
|---|---|
| Width | 200-300px, not full width |
| Height | 44-50px minimum (tap target) |
| Color | High contrast with background |
| Text | Action verb + outcome: "Start Free Trial" |
| Shape | Rounded corners (4-8px border-radius) |
| Placement | Above the fold, repeated at bottom for long emails |
| Quantity | ONE primary CTA per email |
HTML buttons render differently across email clients. Use the "bulletproof button" technique (VML for Outlook, HTML/CSS for everything else):
| Rule | Why |
|---|---|
| Single column layout | Multi-column breaks on mobile |
| Font minimum 14px | Smaller is unreadable |
| CTA button minimum 44px tall | Apple/Android tap target |
| Images scale to 100% width | Prevent horizontal scroll |
| Stack elements vertically | Side-by-side breaks on narrow screens |
| Test on Gmail app, Apple Mail, Outlook | The big 3 email clients |
60%+ of emails are opened on mobile. Design mobile-first.
| Factor | Rule |
|---|---|
| Image-to-text ratio | Max 40% images, 60% text (spam filters flag image-heavy emails) |
| Alt text on images | Always — images blocked by default in many clients |
| Unsubscribe link | Required by law (CAN-SPAM, GDPR) — make it easy to find |
| From name | Recognizable person or brand name |
| Reply-to | Real address, not no-reply@ (hurts deliverability) |
| List hygiene | Remove bounces, clean inactive subscribers quarterly |
| SPF/DKIM/DMARC | Technical authentication — set up once, critical for inbox |
| Mistake | Problem | Fix |
|---|---|---|
| No preview text | Shows "View in browser" or random code | Set preview text intentionally |
| Image-only emails | Blocked images = blank email + spam risk | 60%+ text, alt text on images |
| Multiple CTAs | Decision paralysis, lower click rate | One primary CTA per email |
| Tiny text | Unreadable on mobile | Minimum 14px body, 22px headings |
| no-reply@ sender | Hurts deliverability, feels impersonal | Use real reply address |
| No mobile testing | Broken layout for 60%+ of readers | Test on Gmail app + Apple Mail |
| Missing unsubscribe | Illegal (CAN-SPAM) + spam complaints | Clear unsubscribe link in footer |
| Over-designing | Email clients render CSS inconsistently | Simple layouts, inline styles |
| Fake urgency | Erodes trust, trains users to ignore | Only use real deadlines |
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