ApiAttributes.cs

using System;

namespace Documentation
{
    [AttributeUsage(AttributeTargets.Method)]
    public class ApiMethodAttribute : Attribute
    {
    }

    public class ApiDescriptionAttribute : Attribute
    {
        public ApiDescriptionAttribute(string description)
        {
            Description = description;
        }

        public string Description { get; }
    }

    [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.ReturnValue)]
    public class ApiIntValidationAttribute : Attribute
    {
        public ApiIntValidationAttribute(int minValue, int maxValue)
        {
            MaxValue = maxValue;
            MinValue = minValue;
        }

        public int? MaxValue { get; }
        public int? MinValue { get; }
    }

    [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.ReturnValue)]
    public class ApiRequiredAttribute : Attribute
    {
        public ApiRequiredAttribute(bool required = true)
        {
            Required = required;
        }

        public bool Required { get; }
    }
}