Fix a ride or run in your browser, then send a clean copy to Strava, Garmin Connect, or wherever you log your training. It's free, and the file never gets uploaded.
Crop out a part you don't want, like a warm-up or the drive home you forgot to stop recording. Strava only lets you trim the start and end of a ride or run, so you need a tool like this to edit or cut something out of the middle. Drag across it, hit Cut, and the laps and totals sort themselves out.
Bad data is just as quick to clean up. Cap a heart rate spike from a dry strap, smooth a power dropout, or pull a wandering GPS point back onto the road. You can also change the device or sport, shift the start time, join two rides into one after a watch dies partway, or rescue a file that won't upload after a crash.
Jump straight to what you want to do:
Building something with FIT files? Read the FIT format reference for developers and AI agents.
Garmin, Wahoo, COROS, Suunto, Polar, Hammerhead, Zwift, Apple Watch through HealthFit, and anything else that writes a standard .FIT file.
FIT stands for Flexible and Interoperable Data Transfer, the format Garmin built to pack a whole workout into one small file. It records your position, heart rate, power, cadence, and more a few times a second, plus laps and a summary, so it holds far more than a plain GPX track. Nearly every watch and bike computer writes it, and Strava, Garmin Connect, and TrainingPeaks all read it, which is how it became the common language for activity data.
A few other places to view, fix, or convert activity files: