Firebase db rules for social app with profiles and posts

rules.json

{
  "rules": {
    ".read": true,
      
    "profiles": {
      "$user_id": {
        ".read": true,
        ".write": "$user_id === auth.uid"
      }
    },
    
    "posts": {
      "$post": {
        ".read": true,
        ".write": "!data.exists() && newData.child('userId').val() === auth.uid"
      }
    }
  }
}