About

A small set of tools for activity files, run by one independent developer.

Why it exists

Fixing or joining an activity file usually means either buying desktop software for a one-off problem or uploading the file, with your home location in it, to someone's server. Neither is necessary. A FIT file is small and the work is simple enough for a browser to do on its own.

How it is built

The FIT reader and writer were written for this site from the published protocol description. The code was written with the help of AI coding tools and is covered by automated tests, including checks against real device recordings and against a separate open-source decoder. The guides were drafted with AI assistance and their platform-specific steps were checked against the official help pages listed at the end of each one.

Nobody here claims to have tested every device or every platform. Where something has not been verified, the page says so.

How it is paid for

The tools are free. The site costs almost nothing to run because your browser does the work. If that changes, for instance if advertising or paid extras are added, this page and the privacy pagewill say exactly what changed.