A better stack for your Firebase Rules - Bolt example

rules.bolt

// Indicates if a user is logged in
imLoggedIn() {
  auth != null
}

// Checks for the correc user id
myUidIs(uid) {
  imLoggedIn() && auth.uid == uid
}

// Checks if user is the server
imServer() { 
  myUidIs('SERVER')
}

// User Profile type
type User {
  displayName: String,
  age: Number
} 

// Adds server read access to all profiles at once (allows search)
path /users { read() { imServer() } }

// User rules for read and write
path /users/{userId} is User {
  read() { myUidIs(userId) }
  write() { myUidIs(userId) || imServer() }  
}