// Write or rewrite transactional and growth emails (invitations, onboarding, referrals, re-engagement) using startup email copy principles from YC/Airbnb. Use when asked to "write an email", "rewrite this email", "invitation email", "onboarding email", or when reviewing email copy for conversion.
Audit and improve marketing copy aimed at engineers — READMEs, landing pages, feature pages, tweets, launch posts. Based on Michael Seibel's YC pitch framework adapted for developer tools. Use when asked to "review copy", "audit the homepage", "improve the README", "check the marketing", or when writing new marketing content for a dev tool.
Review code changes, a plan, a live page (running dev server), or a local HTML file with crit inline comments. Use when asked to review code, a plan, a diff, or a running web app, when you want structured human feedback on your work, or when authoring crit comments programmatically. Covers the interactive review loop plus crit comment, crit share, and GitHub PR sync.
Use when validating a feature request, user feedback, or product idea. Generates Mom Test-style questions that ask about past behavior instead of hypothetical futures. Use when asked to "validate this idea", "mom test questions", "interview questions for this feature", or given a feature request to evaluate.
Generate multiple design explorations for a UI feature, each inspired by a different company's design language. Spawns parallel agents that research a company's style, then implement a standalone HTML prototype. Use when asked to "explore designs", "design options", "compare UI approaches", or "design sprint".
| name | startup-email |
| description | Write or rewrite transactional and growth emails (invitations, onboarding, referrals, re-engagement) using startup email copy principles from YC/Airbnb. Use when asked to "write an email", "rewrite this email", "invitation email", "onboarding email", or when reviewing email copy for conversion. |
Write transactional and growth emails that convert. Based on patterns from YC-backed companies: Airbnb's referral email (Gustaf Alstromer), Dropbox's referral program (Drew Houston), and invitation emails from Stripe, Linear, and Brex.
Every email competes with 50 others in an inbox. You get the subject line and one preview sentence to earn the open. You get the headline and one paragraph to earn the click. Everything else is noise.
The highest-converting referral email ever measured at Airbnb followed this exact structure:
{Person} invited you to {Product} (personal, from a human, not a brand){Person} via {Product} (feels like a forwarded message, not marketing){Person} sent you $40 for your first trip!On Airbnb since 2009). Builds trust — a real person you know vouches for this.Dropbox referrals drove 35% of daily signups at peak. The key insight: emails tied to a specific shared folder ("Alex wants to share 'Q3 Designs' with you") converted far better than abstract product invitations. When Dropbox A/B tested reward amounts, doubling the free storage didn't double conversions — the social trigger (friend's name + shared content) mattered more than the incentive.
Apply this: If the invitation has context (a workspace, a project, a review), name it. {Name} invited you to join {Org} beats {Name} invited you to {Product}.
Brex A/B tested their invite emails and found that removing all feature descriptions and keeping only the social invitation increased click-through rates. Linear follows the same pattern — one line of context, one button, nothing else.
For developer tools especially: under 50 words in the body. Developers scan, they don't read marketing.
| Do | Don't |
|---|---|
| Lead with a person's name | Lead with your product name |
| State the action: "invited you", "shared with you" | Use passive voice: "You've been invited" |
| Keep under 40 characters — 6 words or fewer (mobile truncation at ~50, but shorter wins) | Add brackets, emojis, or ALL CAPS |
| Make it feel like a notification, not marketing | Use "Re:" or "Fwd:" tricks |
Pattern: {Name} {action} you to {thing} — this reads as a personal notification in every inbox.
Use {Person} via {Product}, not {Product} alone. The "via" pattern:
The headline is the subject line expanded, not repeated. It should:
Pattern: {First name} invited you to join {Org}!
One paragraph. Two sentences maximum. It must:
Just accept by **May 22, 2026** to join as a member.Don't:
The body copy should make sense to someone who has never visited your site. The inviter is vouching for your product to their colleague — write copy worthy of that trust.
One button. One action. Nothing else.
Accept invitation not Go to dashboardBelow a divider, show the inviter as a real person:
On {Product} since {month year} — mirrors Airbnb's pattern, builds trustThis section answers the unconscious question: "Is this legit?" A real photo and a tenure date say yes.
Minimal. One line: "If you didn't expect this email, you can safely ignore it."
Don't:
The hidden preview text that appears after the subject in inbox list views. Without it, email clients pull the first visible text (often your logo text or "View in browser").
Add a hidden div as the first element in <body>:
<div style="display: none; max-height: 0; overflow: hidden;">
{First name} invited you to join {Org} — accept by {date}
</div>
Keep it under 100 characters. It should reinforce the subject line, not repeat it.
Not about copy, but these prevent your good copy from rendering as garbage:
lang="en" on <html> — accessibility<meta name="viewport" content="width=device-width, initial-scale=1.0"> — mobile rendering<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> — character encodingrole="presentation" on layout tables — screen readers<style> blockstext_body and html_body — plaintext fallback for terminal clients and accessibility toolsSpam triggers — avoid these in subject and body:
no-reply@ with no SPF/DKIM/DMARCDesign killers:
Trust destroyers:
Paul Graham's test: if you wouldn't send it to yourself, don't send it.
When writing or reviewing an email, verify:
{Person} via {Product} pattern