A Json.NET JsonConverter that can handle converting the following values into boolean values: true, false, yes, no, y, n, 1, 0.

BooleanJsonConverter.cs

using System;
using Newtonsoft.Json;

namespace JsonConverters
{
    /// <summary>
    /// Handles converting JSON string values into a C# boolean data type.
    /// </summary>
    public class BooleanJsonConverter : JsonConverter
    {
        #region Overrides of JsonConverter

        /// <summary>
        /// Determines whether this instance can convert the specified object type.
        /// </summary>
        /// <param name="objectType">Type of the object.</param>
        /// <returns>
        /// <c>true</c> if this instance can convert the specified object type; otherwise, <c>false</c>.
        /// </returns>
        public override bool CanConvert( Type objectType )
        {
            // Handle only boolean types.
            return objectType == typeof( bool );
        }

        /// <summary>
        /// Reads the JSON representation of the object.
        /// </summary>
        /// <param name="reader">The <see cref="T:Newtonsoft.Json.JsonReader"/> to read from.</param>
        /// <param name="objectType">Type of the object.</param>
        /// <param name="existingValue">The existing value of object being read.</param>
        /// <param name="serializer">The calling serializer.</param>
        /// <returns>
        /// The object value.
        /// </returns>
        public override object ReadJson( JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer )
        {
            switch ( reader.Value.ToString().ToLower().Trim() )
            {
                case "true":
                case "yes":
                case "y":
                case "1":
                    return true;
                case "false":
                case "no":
                case "n":
                case "0":
                    return false;
            }

            // If we reach here, we're pretty much going to throw an error so let's let Json.NET throw it's pretty-fied error message.
            return new JsonSerializer().Deserialize( reader, objectType );
        }

        /// <summary>
        /// Specifies that this converter will not participate in writing results.
        /// </summary>
        public override bool CanWrite { get { return false; } }

        /// <summary>
        /// Writes the JSON representation of the object.
        /// </summary>
        /// <param name="writer">The <see cref="T:Newtonsoft.Json.JsonWriter"/> to write to.</param><param name="value">The value.</param><param name="serializer">The calling serializer.</param>
        public override void WriteJson( JsonWriter writer, object value, JsonSerializer serializer )
        {
        }

        #endregion Overrides of JsonConverter
    }
}

If you try this:

namespace ConsoleApp1
{
    public class BooleanJsonConverter {...}

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine($"\"true\" -> {JsonConvert.DeserializeObject<bool>("true")}");
            try
            {
                Console.WriteLine($"\"yes\" -> {JsonConvert.DeserializeObject<bool>("yes", new BooleanJsonConverter())}");
            }
            catch (Exception e)
            {
                Console.WriteLine($"Exception: {e}");
            }
      }
}

You will get this:

"true" -> True
Exception: Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: y. Path '', line 0, position 0.
   at Newtonsoft.Json.JsonTextReader.ParseValue()
   at Newtonsoft.Json.JsonTextReader.Read()
   at Newtonsoft.Json.JsonReader.ReadForType(JsonContract contract, Boolean hasConverter)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonConverter[] converters)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonConverter[] converters)
   at ConsoleApp1.Program.Main(String[] args) in C:\Users\ryanj\PersonalDev\ConsoleApp1\ConsoleApp1\Program.cs:line 247

which is exactly the same failure mode as described by this SO post, for which this very Gist was proposed as a solution.

You are trying t o deserialize the input yes into a bool. This is not a valid JSON string. Try it with "yes" instead:

bool yes = JsonConvert.DeserializeObject<bool>("\"yes\"", new BooleanJsonConverter())

It worked for me in my case and as I implemented it in a .net 6 service I added it to program.cs so that it would work for all requests. Thank you very much for sharing this.

var builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers().AddNewtonsoftJson(options => { options.SerializerSettings.Converters.Add(new BooleanJsonConverter()); });