Stamplyn

Stamplyn started as one of my co-founders’ ideas: an app to book a whole trip in one place, from the flights and the hotel to museum tickets and getting around. That’s how we started building it, with stamps as one feature among many.

The more research I did, the less I believed in it. Plenty of apps had tried to be the one place for all your bookings, and many of them failed. And I doubted people would trust a new app with all of theirs. The stamps were the part no one else had, so I proposed dropping everything else and building only them, and the team backed it. Rick Rubin calls himself a reducer rather than a producer. It’s what I try to be on a new product.

Three of us write the code, all with AI coding agents, and I plan the work. I break each feature into issues, each with a brief an agent can work from: what to build, how it should behave, and when it’s done. I size each piece for whoever picks it up, then review and merge the pull requests. I take on some of the hardest parts myself, but not all of them: hard problems are how a team gets better, so I hand them out too.

A stamp app is only as good as its map, and I didn’t want anyone writing cities by hand. So I built a pipeline that maps a whole country in one command. It starts from Wikidata, the open database behind Wikipedia: every museum, monastery, waterfall, old town, famous street, stadium and race track with coordinates, minus the airports, train stations and anything demolished. OpenStreetMap adds each place’s outline, and Wikivoyage’s “See” lists let in small places Wikipedia barely covers.

Gemma 4, Google’s open model, keeps or drops each place, picks its icon and chooses its name, but only from the names Wikidata already has, and code checks every one. Code, not the model, decides the rest: how famous a place is, from how many Wikipedia languages cover it and how often it’s read; which of the four stamp materials it gets, from paper to holographic; which album it belongs to; and how close you have to be to collect it. A lake counts from anywhere along its shore, and a mountain from the viewpoints that look at it.

Claude agents reviewed the result country by country and cross-checked each other’s calls. Memorials stay in, but quietly, with no points and no confetti, while politically hostile sites and areas under travel warnings are left out. That’s how Stamplyn covers most of the world: over 40,000 landmarks in over 2,000 albums, for a few cents of model time per country.

Every landmark also has a line or two about it, written by Claude Haiku and checked against the place’s Wikipedia article by Claude Sonnet. Audits of random samples found a detail off in about one line in 20 at worst, and none about the wrong place.

The best-known places have their own illustrated stamp, over 1,500 so far, all in one ink-and-wash style. I tried Gemini, Ming Image, Recraft and Meta’s Muse Image on the same 20 landmarks, and Muse got buildings right most often, at about a cent a picture. Words alone kept failing on complicated buildings, so a Claude Sonnet agent now describes each place from a photo of it, Muse draws from that description, and another Sonnet agent compares the drawing with the photo. Where that still goes wrong, Gemini 3 Pro Image redraws straight from the photo, changing only the style.

Then people checked them. We split the pictures between us by country and compared each one with the real place, on a review page I built for it. I marked about one in six of mine as wrong, and a flagged picture goes back to be drawn again, from a photo.

The Wonders, like the Colosseum or Mount Fuji, open to a stamp of their own, with gold-foil lettering that catches the light as you tilt your phone, and a depth map, made with Depth Anything, so the near parts of the picture shift more than the far ones.

Stamplyn is built with Expo and React Native, for iPhone and Android, and I wanted it to feel at home on the phone, not like a website inside an app. So I spent a lot of time studying apps that do: how they respond to a touch, and where they use a sound or a haptic. On iPhone it uses Apple’s new Liquid Glass look.

I designed Stamplyn too: the name, the icon of a stamp with its corner peeled back, and the screens.