pg_isready mandatory parameters?

I found this in PG14 ==>

bash-4.4$ ./pg_isready --version
pg_isready (PostgreSQL) 14.2
bash-4.4$ ./pg_isready
/var/run/postgresql:5432 - no attempt
bash-4.4$ ./pg_isready -h localhost
localhost:5432 - no attempt
bash-4.4$ ./pg_isready -h localhost -p 5432
localhost:5432 - no attempt
bash-4.4$ ./pg_isready -h localhost -p 5432 -d postgres
localhost:5432 - no attempt
bash-4.4$ ./pg_isready -h localhost -p 5432 -d postgres -U postgres
localhost:5432 - accepting connections

I always thought all parameters are optional? No?

Thanks,
Markus