Membership of the pg_monitor role is sufficient for the vast majority of this tool's capabilities to work:

CREATE USER pgnow_user WITH PASSWORD 'Y0uRp@s$w0rD';
GRANT pg_monitor TO pgnow_user;

In a small number of places, users with greater permissions will see additional information:

• Generating a generic explain plan, even though the query isn't executed, is only possible when the user has permissions as if they were going to execute that query.
• When exploring vacuum health, information about the data size consumed by dead vs alive tuples is only available for tables the user can select from, even though data isn't actually read.
• pgNow can analyse the pg_hba.conf file to identify security concerns; only a superuser has access to this data.