How Cailloux started

The starting point: nothing existed

On the big races there are chips, timing mats, tracking websites. Everyone knows where you are, to the second. It is comfortable.

On the small races — which is to say the vast majority — there is nothing. No tracking, no position, no splits. Your crew waits at the aid station with one single piece of information: “well… he'll turn up eventually.”

I looked for a tool. I tried a few. None of them did what I wanted: either it was built for organisers and their 4 000 race numbers, or it was a GPS beacon that flattened the battery in 3 hours.

What set it off: the Trail de la Chouffe

July 2026. I was due to run the Trail de la Chouffe, with a real support crew waiting for me at the aid stations. People who take a day off, who drive out, who set up a chair and a bowl of soup for you.

And those people were going to spend the day doing one single thing: wondering where I was.

I thought: I have to give them my pebbles.

Like Hansel and Gretel. I drop a marker at every checkpoint, they follow my trail. Except that instead of pebbles in a forest, they are check-ins in an app. And instead of birds eating everything, there is temperamental 4G — but we planned for that.

The real foundation: my paper cards

Before the app there was paper. For years, before every solo race, I made myself 2 small cards, laminated them, and slipped them into my jacket.

The first: the checkpoints, the distance marks, my expected arrival time, my departure time, and the cut-off. A colour code per aid station, to find the right line at a glance when your eyes no longer really work.

The second: nutrition, hour by hour. 0:45 bar. 1:30 half a MulleBarre. 2:30 gel. Because the one thing I am absolutely certain of is that I will never think to eat on my own.

The ancestor of Cailloux: 2 sheets of paper, a laminator and a lot of highlighter.

From the card to the app

Cailloux is nothing more than those 2 cards. I simply went through them, line by line, asking myself each time: what if the app could do a little more than the paper?

Expected time→ recalculated live from how far ahead or behind you actually are
Cut-off time→ an alert when it gets tight, before it is too late
The distance mark→ the altitude profile and the map, with your estimated position
The nutrition plan→ a notification at the appointed hour, even with the phone locked
The colour code→ kept. It was fine as it was.

Then I added what paper could never do, laminated or not: my crew sees the same thing I do, live, on their phone. They get a notification at every check-in. They know what time to take the bottles out of the bag.

And we can write to each other. A real message, short, that gets through even when a call would not. “Get the Coke ready.” 3 words that change the end of a race.

Why does it work with no signal? Because the paper card worked with no signal. That was the bar not to quietly lower: if the app is less reliable than a piece of plastic in a pocket, it is useless. So check-ins are kept on the phone and leave on their own as soon as the signal returns — and the nutrition reminders ring even in the middle of a dead zone. 🪨

And now?

The app exists, it runs, and it is free — version 1.0 came out on 31 August 2026, 1.1 on 5 October, and 1.2 has been in beta since 19 October. It was designed by someone who runs, for people who run — and above all for those who wait at the roadside with a folding chair and a flask.

It is not perfect. It still has bugs. But it already does better than my laminated sheet of paper, and honestly, that was my only goal to begin with.

Want to try it?

Any distance, any race, any support crew bored stiff at an aid station.

🪨 Build my race