C# – JSON object contains a trailing comma at the end which is not supported

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Problem

When you deserialize JSON with a “trailing comma”, you get the following error:

The JSON object contains a trailing comma at the end which is not supported in this mode. Change the reader options.

JSON properties are separated with commas. A trailing comma is one that has no properties after it. Here’s an example of a trailing comma:

{
    "id":123,
    "title":"Jurassic Park",
}
Code language: JSON / JSON with Comments (json)

This is technically invalid JSON (according to the official JSON spec), but it’s really not a good reason for deserialization to fail. You can update the serializer to allow trailing commas.

Solution

To allow trailing commas, set the JsonSerializerOptions.AllowTrailingCommas to true, like this:

using System.Text.Json;

var movieJson = "{\"id\":123,\"title\":\"Jurassic Park\",}";

var options = new JsonSerializerOptions()
{
    AllowTrailingCommas = true
};

var movie = JsonSerializer.Deserialize<Movie>(movieJson, options);
Code language: C# (cs)

Note: If you’re using ASP.NET Core, read how to change the JSON serialization settings.

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