Short Links
VRChat has several ways users can share links to instances, users, and groups.
Canonically, the URLs that many people will use are those they see in their browser, starting with https://vrchat.com/home/....
But there are other URLs for users, groups, worlds, and instances that offer brevity.
Each of the following describes an HTTP GET request, where VRChat replies with an HTTP 302 Found and the target URL in the Location header of the response.
Users
https://vrch.at/<userId> redirects to https://vrchat.com/home/user/<userId>
Worlds
https://vrch.at/<worldId> redirects to https://vrchat.com/home/world/<worldId>
Instances
https://vrch.at/<shortName> redirects to https://vrchat.com/i/<shortName>
https://vrchat.com/i/<shortName> redirects to https://vrchat.com/home/launch?worldId=<worldId>&instanceId=<instanceId>&shortName=<shortName>
Groups
https://vrc.group/<groupCodeAndDisc> redirects to https://vrchat.com/api/1/groups/redirect/<groupCodeAndDisc>
https://vrchat.com/api/1/groups/redirect/<groupCodeAndDisc> redirects to https://vrchat.com/home/group/<groupId>
This last one is actually programmatically useful, as it can be used to resolve a group code with discriminator to the group's ID without having to use the 'search groups' API endpoint.
Ex.: GET https://vrchat.com/api/1/groups/redirect/VRCHAT.0000 redirects to https://vrchat.com/home/group/grp_7ccb6ca3-cd36-4dab-9ab1-7bcf08d794e4