Check a FIT file is your Garmin activity file corrupt? Find out in a few seconds

What the check looks at

• Structure

  The header, the data size it announces, the CRC checksum at the end, a last message cut in the middle, damaged bytes, extra bytes after the end.

• Summary

  Whether the session and activity messages exist, as they would if the activity was saved normally, and whether laps and totals agree.

• Times

  Points dated before 2000 or in the future, times going backwards, long holes in the recording without a pause.

• Positions and sensors

  GPS points at 0°, 0°, outside the globe or jumping across the map; heart rate above 240 bpm, power above 2,500 W.

• Sport

  A sport that does not match the speed of the activity, such as a ride saved as a run.

• File type

  Whether the file is an activity at all: courses, settings or health files are recognised as such.

Reading the verdict

“No problem found” means the file follows the FIT protocol and every check passed. If an app still refuses it, the reason is elsewhere: a duplicate of an activity already imported is the most common one.

“Readable, with data problems” means the file opens but some values are wrong (GPS jumps, spikes, a hole). Apps usually import it, with wrong numbers.

“Damaged file” means at least one problem that usually makes an upload fail. The repairs are proposed right below the diagnosis, on the same page.

Example: a run from a watch that ran out of battery

This is what the check finds on the sample file “Run from a crashed watch” offered above the drop zone:

Wrong data size in the header

The watch stopped before closing the file.

Incomplete last message

The last bytes belong to a record that was never finished.

Session summary missing

No distance or duration was saved for the activity.

Activity message missing

The file was never closed as an activity.

All four are repairable: the file is rewritten with the right size and checksum, and the summary is rebuilt from the 1,800 recorded points.

Questions