Case study
Sumzap: a group chat’s year, in three cards.
We designed, built and launched Sumzap, a web app that turns a WhatsApp group chat into a year in review, from a written spec to taking payments in two days.
Project record
The brief
Every December, apps tell you what you listened to and watched all year. Nobody did it for the group chat, which is where a lot of people’s year actually happens.
The constraints made it interesting: chats are deeply personal, so they couldn’t be uploaded; nearly everyone would arrive on a phone, from a link, with no app to install; and at £1.23, paying had to take one tap and running costs had to stay tiny.
What we built
1Private by design
Group chats are personal, so the chat file is never uploaded. The phone reads it and works out the stats in the browser. For the awards, only a small trimmed sample is sent, with phone numbers, emails, links and addresses stripped first, and it’s deleted straight after. Results delete themselves after 30 days.
2Funny, not cruel
An AI writes the awards and the verdict, picking the twelve that fit each group from a pool of 36. Guardrails keep it to affectionate British banter, steer clear of sensitive subjects, and soften the tone when a chat has been through something hard.
3Built to be shared
Each card is drawn as a Story-sized image that matches the screen exactly. One group link unlocks everything for everyone in the chat, and shared links show a proper preview in WhatsApp and LinkedIn.
4Payments in one tap
Apple Pay, Google Pay or card through Stripe, at £1.23. Consumer law consent is built into the checkout, receipts double as the written confirmation, and duplicate or orphaned payments are refunded automatically.
5Runs itself
An admin dashboard shows the funnel from visit to share, sales and failed uploads by day and by source. Offer codes handle free trials, price tests run behind a switch, and email alerts flag AI spend, error spikes and card disputes.
Under the bonnet
No servers to patch, nothing to scale by hand, and hosting that costs pennies until it needs to cost more.
What this means for your site
The same care goes into every site we build and look after: fast on a phone, careful with your customers’ data, and watched so problems are caught before your customers notice.