max:value

• The field under validation must be less than or equal to a maximum value.Strings and numerics are evaluated in the same fashion as the size rule.

data = %{
    name: "john",
    age: 20
}
rules = [
    %{
      field: "name",
      validate: ["max:10"]
    },
    %{
      field: "age",
      validate: ["max:40"]
    }
  ]