Migration tools like System.Text.Json 's source generator can help, but many teams have simply decided: if it ain't broke, don't fix it.

Enables validation of JSON data against a defined schema using the IsValid method. Usage Context Json.NET - Newtonsoft

public override void WriteJson(JsonWriter writer, DateTime value, JsonSerializer serializer) => writer.WriteValue((value - new DateTime(1970, 1, 1)).TotalSeconds); public override DateTime ReadJson(JsonReader reader, Type objectType, DateTime existingValue, bool hasExistingValue, JsonSerializer serializer) => new DateTime(1970, 1, 1).AddSeconds(Convert.ToDouble(reader.Value));