Comparing the Performance of System.Text.Json and Newtonsoft.Json in .NET Core

Erick McCollum | 01 Mar 2020

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Along with the release of .NET Core 3.0 came a new namespace for working with JSON data: System.Text.Json. Prior to this, the primary API for working with JSON data in .NET was through the use of Newtonsoft’s Json.NET, a third-party package. However, with the introduction of System.Text.Json comes a new, built-in way to work with JSON data.

In this article, I will be comparing the performance of basic JSON serialization using both the System.Text.Json and Newtonsoft.Json APIs.

Performance Test Overview

I will be performing a very basic performance test using a .NET Core 3.1 console application. Within this console application, I have created a minimal “Note” class that contains three properties: “Id” (integer), “Title” (string), and “NoteText” (string). Please find a code snippet of the “Note” class below:

    class Note 
        public int Id { get; set; } 
        public string Title { get; set; } 
        public string NoteText { get; set; } 
        public Note() {} 
        public Note(int id, string title, string text) 
            this.Id = id; 
            this.Title = title; 
            this.NoteText = text; 

I will create one million (1,000,000) instances of this “Note” class, and then add them to a List object. Then, I will use both the System.Text.Json and Newtonsoft.Json APIs to serialize this List to a JSON string ten times each. I will capture timings during each serialization process. Therefore, at the end of this test I will have ten performance timings for both the System.Text.Json and Newtonsoft.Json APIs.

Below is a code snippet showing how the list will be serialized, and how the timings will be captured, for both the System.Text.Json and Newtonsoft.Json APIs:

    public static int SysJsonSerializeTimer(List<Note> noteList) 
        Stopwatch sw; 
        sw = Stopwatch.StartNew(); 
        return (int)sw.ElapsedMilliseconds; 
    public static int NsJsonSerializeTimer(List<Note> noteList) 
        Stopwatch sw; 
        sw = Stopwatch.StartNew(); 
        return (int)sw.ElapsedMilliseconds; 

The full code used for this performance test may be found in my GitHub repository at the following link: SerializationWithSystemTextJson.


The performance results from this console application may be seen below:

    1              1293                     2058 
    2              654                      1570 
    3              879                      1202 
    4              907                      1342 
    5              955                      1220 
    6              892                      1208 
    7              921                      1214 
    8              922                      1288 
    9              895                      1219 
    10             884                      1229 

    AVG            920.2                    1355 

As can be seen above, the System.Text.Json API performs better than the Newtonsoft.Json API in all ten iterations of this basic performance test. On average, the System.Text.Json API completed the JSON serialization process in about 68% of the time that it took the Newtonsoft.Json API to serialize the same data. This means that there was a 32% (about 1.3x) performance improvement when using the new System.Text.Json namespace.


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