nadekobot/src/NadekoBot/_common/JsonConverters/NumberToStringConverter.cs

using System.Globalization;
using System.Text.Json;
using System.Text.Json.Serialization;

public class NumberToStringConverter : JsonConverter<object>
{
    public override bool CanConvert(Type typeToConvert)
        => typeof(string) == typeToConvert;

    public override object Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        switch (reader.TokenType)
        {
            case JsonTokenType.Number:
                return reader.TryGetInt64(out var l)
                    ? l.ToString()
                    : reader.GetDouble().ToString(CultureInfo.InvariantCulture);
            case JsonTokenType.String:
                return reader.GetString() ?? string.Empty;
            default:
                {
                    using var document = JsonDocument.ParseValue(ref reader);
                    return document.RootElement.Clone().ToString();
                }
        }
    }
    
    public override void Write(Utf8JsonWriter writer, object value, JsonSerializerOptions options)
        => writer.WriteStringValue(value.ToString());
}