gpx.studio is an online free GPX viewer and editor with lots of features :
- visualize multiple files in different colors and aided by many different maps (cycling, hiking, satellite, Strava heatmap overlay, etc)
- edit traces by adding, inserting, moving or deleting points
- reverse traces
- simplify traces
- add timestamps to a file
- view, add, edit and remove waypoints
- automatically add elevation data to traces if missing
- merge multiple files, extending time, heart rate, cadence and temperature data where needed
- extract segments from traces and perform any other action while maintaining the segments' structure within files
- save the result on your computer or to your Google Drive™ to get a shareable link and code to embed the map on your website