Design referral programs and viral growth loops. Use when asked to create referral systems, viral mechanics, word-of-mouth campaigns, or growth loops.
Library skill — the default version is maintained in GitHub; edits you make live in your own clone.
Design effective referral programs and viral loops that drive sustainable growth.
Only the referrer gets rewarded.
Best for: - Products with strong organic word-of-mouth - Low-friction signups where the referred user needs no extra motivation - Cost-sensitive businesses
Examples: - Uber: "$10 credit for every friend you refer" - Amazon Associates: Commission on referred purchases
Template:
Refer a friend and get [reward].
Share your unique link: [referral_url]
Both referrer and referred user get rewarded.
Best for: - Products requiring activation effort from new users - Competitive markets where new users need a nudge - Subscription businesses
Examples: - Dropbox: Both get 500MB extra storage - Airbnb: Referrer gets $25 credit, friend gets $40 off first stay - PayPal: Both get $10 when friend makes first transaction
Template:
Give [friend_reward], get [referrer_reward].
Share your link and you both win: [referral_url]
Rewards increase with number of successful referrals.
Example tier structure: | Referrals | Reward | |-----------|--------| | 1 | Free month | | 3 | Exclusive feature unlock | | 5 | Premium plan for 3 months | | 10 | Lifetime premium access | | 25 | Cash payout or swag box |
Best for: - Creating power referrers / ambassadors - Products with passionate user bases - Building a referral leaderboard culture
The viral coefficient (K-factor) determines whether your referral loop is self-sustaining.
K = i * c
Where:
i = number of invites sent per user
c = conversion rate of each invite
If K > 1: viral growth (each user brings more than one new user)
If K < 1: referrals supplement but don't replace other acquisition
Users send an average of 5 invites (i = 5)
15% of invites convert to signups (c = 0.15)
K = 5 * 0.15 = 0.75
With 1,000 initial users:
- Cycle 1: 1,000 * 0.75 = 750 new users
- Cycle 2: 750 * 0.75 = 563 new users
- Cycle 3: 563 * 0.75 = 422 new users
- Total after 10 cycles: ~3,570 additional users from referrals
The speed of the viral loop matters as much as K:
Effective growth = K / cycle_time
A K of 0.5 with a 1-day cycle > K of 0.8 with a 30-day cycle
| Lever | Action |
|---|---|
| Increase invites (i) | Make sharing frictionless, prompt at key moments |
| Increase conversion (c) | Better landing page, stronger incentive, social proof |
| Reduce cycle time | Instant reward delivery, real-time notifications |
Pros: High conversion, personal, trackable Cons: Lower volume, requires email access
Template:
Subject: I thought you'd like [Product] -- here's [reward] to try it
Hey [Name],
I've been using [Product] for [time] and it's been great for [specific benefit].
I wanted to share my referral link so you can get [friend_reward]:
[referral_url]
[Your name]
Pros: High reach, low effort, viral potential Cons: Lower conversion rate, less personal
Platform-specific templates:
Twitter/X:
I just [achievement/milestone] with @Product! If you want to try it,
use my link and we both get [reward]: [referral_url]
LinkedIn:
I've been using [Product] to [professional benefit] and the results
have been impressive: [specific metric].
If you're looking for [solution], here's my referral link
(we both get [reward]): [referral_url]
WhatsApp/SMS:
Hey! I've been using [Product] and really like it. They have a
referral deal -- we both get [reward] if you sign up through my link:
[referral_url]
Pros: Highest intent, contextual, frictionless Cons: Only reaches existing users
Best practices: - Show referral prompt after a success moment (completed task, achievement, positive outcome) - Pre-populate sharing message - Show referral progress and rewards earned - Add referral widget to account/settings page
| Method | Pros | Cons |
|---|---|---|
| Unique link | Frictionless, works in any channel | Harder to share verbally |
| Referral code | Easy to remember, shareable verbally | Extra step at signup |
| Both | Maximum flexibility | More complex to implement |
The page a referred user sees when they click the referral link.
[Hero Section]
- Headline: "[Referrer's name] invited you to [Product]"
- Subheadline: "Sign up now and get [friend_reward]"
- CTA button: "Claim your [reward]"
[Social Proof]
- "[Referrer's name] and X others use [Product]"
- Logos of known customers
- Key metric: "Trusted by X users"
[Value Proposition]
- 3 key benefits with icons
- Brief product description
[How It Works]
- Step 1: Sign up (takes 30 seconds)
- Step 2: [Key activation action]
- Step 3: Enjoy [reward] + the product
[CTA Repeat]
- "Join [Referrer's name] on [Product]"
- Urgency: "This offer expires in [X days]"
[FAQ]
- When do I get my reward?
- What does [Product] do?
- Is there a catch?
| Decision | Options |
|---|---|
| Reward type | Cash, credit, product features, swag, charity donation |
| Reward timing | On signup, on activation, on first purchase |
| Reward amount | Test multiple amounts; higher is not always better |
| Expiration | Referral links expire after X days? Rewards expire? |
| Limit | Max referrals per user per month? |
| Eligibility | All users or only paid/active users? |
Subject: You have [X] invites waiting
Hey [Name],
Did you know you can give your friends [reward] and get [reward] for yourself?
You've invited [0/N] friends so far. Share your link:
[referral_url]
Here's what [Product] users are saying:
"[Testimonial]" -- [Customer name]
Subject: [Referrer] sent you a gift -- [reward] inside
Hey there!
[Referrer's name] thinks you'd love [Product], so they're giving you [reward] to try it.
[CTA: Claim your reward]
What is [Product]?
[1-sentence description]
What you'll get:
- [Benefit 1]
- [Benefit 2]
- [Benefit 3]
- Plus [friend_reward] from [Referrer's name]
This offer expires in [X] days.
Subject: [Friend's name] just signed up -- you earned [reward]!
Great news, [Name]!
[Friend's name] accepted your invitation and signed up for [Product].
Your [reward] has been added to your account.
Keep sharing: you've referred [X] friends so far.
[referral_url]
[Show progress toward next tier if using tiered rewards]
| Metric | Formula | Good Benchmark |
|---|---|---|
| Participation rate | Users who share / total users | 15-25% |
| Shares per user | Total shares / participating users | 3-5 |
| Click-through rate | Link clicks / shares | 20-40% |
| Conversion rate | Signups / link clicks | 10-25% |
| Viral coefficient (K) | Invites * conversion rate | 0.3-0.7 typical |
| Viral cycle time | Avg days from invite to new user's first invite | 1-7 days |
| Referral revenue | Revenue from referred users | Track separately |
| CAC via referral | Reward cost / acquired users | Compare to paid CAC |