Upload your .FIT file to have it automatically analyzed by the tool. If any corruption is detected, you’ll see a repair button—click it to try fixing the file and then download the repaired version. If that doesn’t work, remember that the Merge Tool also includes a different type of repair feature that might help. If your file seems fine but you notice some items marked as invalid or highlighted in red, DON'T WORRY! This usually doesn’t mean your file is corrupted. Many of these fields are just undocumented by Garmin, and I’m gradually adding more information about them as users help identify what each field means. Any name field or message with a star (*) is not an officially documented FIT field and should be treated with caution.