JoinContest creates a participant record for the calling user without an organiser being involved, and only in a contest whose visibility lets people in on their own. The contest decides whether such self-joined participants compete officially.

In a team contest the captain joins on behalf of the team, naming the members who compete. The roster must fit the contest's team size, and a member can be on only one roster in a contest. Until the team starts the contest, the captain can call it again to change the roster.