A Mario Universalis project / Case study
Mario Kart
World Guessr.
I launched Mario Kart World Guessr on 21 June 2025, shortly after Mario Kart World came out. With people exploring the new game, it felt like a good time to try a simple idea: could you find where a screenshot was taken on its map?
As with many of my personal projects, this was supposed to be a quick little thing. It got a little out of hand.
- My role
- Solo design, development & maintenance
- Launched
- games played
- 65,360
- accounts created
- 1,510
- photos
- 1,700
- published contributors
- 140
Figures recorded in September 2026. You can play without an account. Accounts and players are not the same thing.
One photo. A whole map to search.
The idea follows the familiar geography-game loop: look at a photo, explore the map, place a marker, and get a score based on the distance from the actual location.
Here, the world is Mario Kart World. I use React Leaflet with a custom map and CRS.Simple. This coordinate system lets me use a map that does not represent the Earth, while keeping Leaflet's zoom and panning controls.
The loop is short: observe, search, make a decision, and find out how far off you were. Or, occasionally, how surprisingly close.
A community behind the camera.
Players can submit their own photos and mark where they took them. That means the game's collection can grow beyond the images I add myself.
Submissions go through a review process before publication. GitHub Issues are part of that review and validation system, rather than the entire moderation process.
- 01Submit a photo
- 02Mark its location
- 03Review and validate
- 04Publish in the game
- community photos submitted
- 1,480
- community photos published
- 1,700
- people who submitted a photo
- 150
- people with a published photo
- 140
Figures recorded in September 2026.
A place for the photographers, too.
Photographers can create albums, pick their favourite photos, put their work on display, and share the collection.
Their images become more than material for the next round. Albums give people a way to explore a collection through the eyes of the person who took the photos.
Something to come back to.
Over time, I added game modes, leaderboards, achievements, unlockable characters, and notifications.
The daily challenge automatically selects 5 different photos each day. It gives players a fresh selection to explore, without requiring me to curate a new set every morning.
Built and maintained on my own.
The frontend uses React and Vite, with React Leaflet for the interactive map. The backend runs on vanilla PHP, with MariaDB for data and ImageKit for images.
I develop and maintain the project alone. Community contributions grow its content, while feedback and actual usage help me decide what to work on next.
Further than I expected.
The game found its way beyond France. I have seen French, English, German and Japanese videos and players. That is an observation, not a country-by-country audience measurement.
Coming across a Japanese video of someone playing a game I built on my own at home is still pretty funny.
When a side project becomes a product.
Mario Kart World Guessr is probably the personal project of mine that feels most like a real product.
At first, decisions mostly came from what I wanted to build. Now they also come from usage, contributions, feedback, and the behaviours I observe.
There is still plenty of room for my own ideas. But what players actually do with the game now matters as much as what I originally imagined for them.