Free FIT/TCX/GPX Diagnostic
Find out why a FIT, TCX, or GPX activity file fails to import — missing points, bad timestamps, GPS jumps, and checksum errors — privately in your browser.
Or drag and drop FIT, TCX, or GPX files here.
- No file selected.
How to diagnose an activity file
- Add one or more .fit, .tcx, or .gpx files.
- Review the report for each file: structural errors, timestamp problems, missing points, and GPS jumps.
- Download a combined text report to share with support or keep for your records.
What this tool checks and what it doesn't
This is a read-only diagnostic tool — it never modifies or repairs your file. For FIT files, it validates the file header, the whole-file checksum, and walks the record structure to find timestamp and position data; it does not decode every possible FIT field, and it reports (rather than guesses at) the rarer compressed-timestamp record format when encountered. For TCX and GPX, it reads every trackpoint's time, position, altitude, and heart rate.
Why use this privately?
Your activity file is parsed entirely in your browser and is never uploaded. That matters for GPS tracks, which can reveal home addresses and daily routines.
Common use cases
- Find out why a GPS watch export won't import into training software
- Spot GPS jumps or missing points before sharing an activity
- Check a FIT file's checksum without special desktop software
Frequently asked questions
Are my activity files uploaded?
No. Parsing and the diagnostic report are produced entirely in your browser.
Can this tool fix a broken file?
No. This is a diagnostic-only tool. It explains what's wrong so you know whether the file is worth trying to repair, but it never changes or exports a modified file.
What causes a FIT file to fail its checksum check?
Usually the file was truncated (an incomplete download or a device that stopped recording mid-write) or altered by a tool that didn't recompute the trailing CRC. A checksum mismatch means the file may be corrupted, not a certainty.
What is a GPS jump?
A sudden, implausible change in position between two closely-timed points — often a sign of a lost GPS signal or file corruption, though real vehicle segments can occasionally trigger this too.
Does this support every FIT file field?
No. It focuses on the fields needed to diagnose common import failures: timestamps, position, altitude, and heart rate. It does not interpret every possible message type in the FIT specification.