Referral loop
A repeatable path where a user invites someone, that person gets value, then becomes able and motivated to invite the next user.
See it
What it is
A referral loop turns a successful user into the source of the next user: they encounter a reason to invite, share a link, the recipient gets value, and the cycle can repeat. Dropbox's classic referral program made the exchange concrete by giving 500 MB of extra storage to both sides, capped once the account had collected enough of them.
Reach for it when using the product naturally exposes someone else to it, or when users know peers with the same problem. Put the invitation after a moment of value, make the reward useful inside the product, and measure every step from invite shown to referred user activated.
Gotcha: a refer-a-friend page is not automatically a loop. If the new user never reaches the point where they can invite someone else, it is a one-time campaign. Cash-like rewards also attract self-referrals, duplicate accounts, and coupon sites, so eligibility and fraud checks belong in the design.
Ask AI for it
Design and implement a referral loop for [product]. Trigger the invite immediately after [verified value moment], issue a unique signed code using HMAC-SHA256, and give [approved reward] only after the referred account completes [activation event]. Instrument PostHog events for invite viewed, link copied, invite opened, signup completed, activation completed, and reward issued. Return the user flow, UI copy, data model, server-side validation logic, reward state machine, and tests for self-referral, duplicate accounts, replayed codes, refunds, and reward caps. Do not invent a reward or eligibility rule.