When one intended ride or run ends up recorded as two or three separate .fit files, battery died and the device restarted, you accidentally hit stop / start at a coffee stop, the head unit recorded the coffee break as its own activity, this tool stitches them back into a single continuous FIT file. Two modes: stitch (treat as one continuous effort with no gap) or preserve (keep the real timestamps, gaps and all). Runs entirely in your browser, no upload.
Two or more files from the same intended activity. They’ll auto-sort by start time. You can reorder or remove any after upload.
or
Sorted oldest first. Use ▲ / ▼ to reorder, ✕ to remove. Gaps between files are shown below each row.
What to do with the time between the end of one file and the start of the next.
This tool covers the sequential case: one activity split across two or more files in time. If you’re trying to combine data recorded simultaneously on two or more devices (e.g. one head unit has power + HR, another has power + Stryd running power + Moxy SmO2), that’s the parallel-merge case and it needs clock alignment, sampling-rate matching, per-field conflict resolution, and developer-field preservation.
That belongs on Grepiac where merges can be saved to your athlete profile and replayed on future activities. It’s coming as part of the Grepiac data-tools build.
Scope & honesty notes
