Convert FIT (device activity file) to TCX

Lap splits are how most training logs make sense of a workout — the hard interval versus the recovery jog, the climb versus the descent — and TCX is the one format on this site that carries that structure through a conversion without any loss. Pull a FIT file off a bike computer or watch and every lap marker it recorded is preserved as a real lap element in the output, not flattened into a single continuous track or reduced to a column of numbers. TCX was built by Garmin for exactly this purpose, so the shape maps cleanly: trackpoints keep their position, elevation, timestamp, heart rate, cadence, and power, second-resolution timestamps replace the FIT file's millisecond precision, and the only channel that doesn't survive is temperature, which TCX's schema has no element for. Because TCX is aimed at training platforms rather than general mapping tools, its element ordering is stricter than GPX's — Garmin Connect and similar validators check for schema-correct sequencing, and this tool writes TCX that conforms to it, so a converted file should import cleanly rather than bouncing back with a validation error. All of the parsing and rewriting happens locally, in a Web Worker inside your own browser tab; the FIT file is never transmitted anywhere, which matters if the activity in question is a route you'd rather not hand to a third-party server just to get a different file extension. If your reason for converting is to keep a lap-by-lap training record intact — interval sets, structured workouts, anything where the boundaries between efforts matter — TCX is the correct target, and this tool produces it for free on files up to 25 MB.