Trim a FIT file
Load the file and open Trim. Move the start and end handles under the speed and heart-rate charts. Points outside the range are removed, distance starts again from zero, and elapsed time, moving time, distance, average and max heart rate, power, cadence, speed and elevation are recalculated for the session and each lap. Upload the result to Garmin Connect, Strava, TrainingPeaks or intervals.icu.
Repair a corrupt FIT file
When Garmin Connect or Strava says a file is corrupt, the device usually stopped writing halfway: low battery, a crash or full memory. Repair keeps everything readable up to the break, drops broken records and timestamps, adds the missing lap, session and activity messages, and rebuilds the header and checksum.
Combine two FIT files
Load both files and open Merge. Points are sorted by time, distance carries on across the join, laps from both files are kept and one session covers the whole activity.
Questions
Are my files uploaded anywhere?
No. The editor is JavaScript running in this tab. Once the page has loaded it works offline.
Will heart rate, power and GPS survive?
Yes. The editor works record by record and copies every field it doesn't change byte for byte, including developer fields written by Connect IQ apps.
Where do I get the .fit file?
From Garmin Connect on the web (activity → ⚙ → Export Original), Strava (⋯ → Export Original) or straight from the watch over USB. Step by step: how to download a FIT file.
Which devices are supported?
Anything that writes FIT activity files: Garmin, Wahoo, Coros, Hammerhead, Bryton, Suunto exports, Zwift and MyWhoosh.