VRCX is a third-party, open-source desktop companion application for VRChat. It is not a mod; it runs alongside VRChat using the VRChat API. It is widely considered safe by the community (though use at your own discretion).
: The ID will be listed in the "Blueprint ID" text field. This links your local Unity project to the specific avatar entry in VRChat's database. how to get avatar id vrchat
The ID is everything after /avatars/