May 2024 — December 2024 · Web · Product · Fullstack Software Engineer @ Callback
Callback is a Tokyo-based startup building a loyalty platform for independent restaurants. As fullstack software engineer, I designed and shipped both the consumer-facing app and the enterprise dashboard.
Designed and built the company's main Next.js/TypeScript site with user-facing leaderboard — grew weekly active users from 25 to 250 in three months. Designed and implemented social features: user profile creation, friend connections, friend activity map, and in-app engagement flows. Built an enterprise dashboard with data visualisations, Stripe payouts, and automated Twilio-mailed reports — increased partner retention by 200%. Orchestrated on GCP Cloud Run with CI/CD pipelines and Docker.
Callback is a loyalty platform but the consumer app doesn't open onto a stamp wallet. I led with a friend activity map instead, because seeing who else has been to your favourite spot, or that a friend stamped somewhere you'd been meaning to try, gives you a reason to open the app on a day with nothing to claim. Filter pills along the bottom let you flip between just yourself, a specific friend, or everyone you follow.
Most loyalty apps treat earned stamps as a private ledger inside a wallet UI. I gave them the Letterboxd treatment instead: a public-feeling collection page, organised by venue, with visit counts. A stamp stops being proof of a transaction and becomes a piece of someone's taste. That changes what the page is for (showing off, not cashing in) and who the audience is (the user's friends, not the operator's till).
The other half of Callback is the restaurant operator. Most loyalty SaaS gives operators a screen per concern: CRM, rewards, payouts, identity, mailer scheduling, analytics. The Callback dashboard is three tabs: My Stamp, Customers, Rewards. Customer counts and recency live on Customers; reward design, claim counts, and the next payout number sit together on Rewards; the store's identity lives inside My Stamp. A non-technical operator can hold three tabs in their head. Fifteen makes them learn the product first, and most won't.