A GPS track contains your home address to the meter. This page states exactly what stays on your device, what leaves it, and how to check it yourself.
Your files are never transmitted. Decoding and analysis run in JavaScript, in your browser, on your device. There is no server to receive them. This is not a policy, it is an absence of infrastructure.
In practice: you can cut your internet connection once the page has loaded, drop your files, and the analysis will work. Only the weather will fail, which is precisely the proof that it is the only thing going out.
| Data | Sent? |
|---|---|
| Your watch file | Never. Read from disk by the browser, analyzed in memory. |
| Your GPS track | Never. |
| Heart rate, paces, power | Never. |
| Max heart rate, threshold pace, race times entered | Never. Kept in memory for the session, and lost when the tab is closed. |
| The generated file | Never by the tool. Only you copy or download it, and what you do with it next is up to you. |
| Route midpoint, rounded | Yes, if weather is enabled. See below. |
| Visit statistics | Yes, anonymous. Cloudflare Web Analytics counts page views, with no cookie and no persistent identifier. Nothing about your files or your workouts. |
A watch's temperature sensor is worn on the wrist and warmed by the body: it reads 3 to 8 °C too high and ignores humidity and wind. Yet heat is the main confounding factor in cardiac drift. Without the real temperature, poor form gets blamed for what is only the normal thermal cost.
The request is therefore built so that it is useless as location data:
The start point is your home. The midpoint is some random place, unrelated to where you sleep.
That is about 1.1 km of resolution. Weather is a regional phenomenon: nothing is lost in accuracy, and the request no longer points to an identifiable place.
No heart rate, no pace, no track, no identifier, no cookie. A rounded latitude, a rounded longitude, a date. The full request looks like this:
https://archive-api.open-meteo.com/v1/archive ?latitude=48.87&longitude=2.34 &start_date=2026-09-23&end_date=2026-09-23 &hourly=temperature_2m,relative_humidity_2m,wind_speed_10m
The recipient is Open-Meteo, an open weather service. The feature can be turned off from a drop-down menu on the home page, and the tool keeps working without it.
The first and last points of a track reveal your front door. The tool removes 250 meters by default, at both start and finish, before any analysis and before any export. The setting can be changed, and an option removes coordinates entirely while keeping the elevation profile, paces and heart rate.
Audience measurement uses Cloudflare Web Analytics: no cookie, no persistent identifier, and no data from your files. It counts page views, countries, traffic sources and device types, never a person.
Do not take our word for it. Open your browser's developer tools (F12), Network tab, then drop a file. You will see the page loading, the audience measurement request to cloudflareinsights.com and, if weather is enabled, one request to open-meteo.com. Nothing else. No request contains the content of your file.
The source code is open, under the MIT license: what the page does can be read line by line.
Since no personal data is collected or stored, there is no record to access, correct or delete: closing the tab erases everything. For any question, the GitHub repository above lets you open a discussion.