Firebase Simple Security Rule Example.js

{
  "rules" : {
    "$user_id" : {
      ".read" : "auth.uid == $user_id", // can read if $user_id matches current user
      ".write" : "auth.uid == $user_id", // can read if $user_id matches current user
      ".validate" : "newData.val().isString()" // new data must be string
    }
  }
}