Newtonsoft.Json vs System.Text.Json — A Senior Developer’s Perspective

After spending over years on building enterprise-scale .NET applications, I’ve learned that choosing the right JSON serialization library can make or break your application’s performance and maintainability.

Well, the well-known package or defaults right now are Newtonsoft.Json and System.Text.Json. I’ll share my experience with both Newtonsoft.Json and System.Text.Json, helping you make an informed decision for your next project!

JSON Handling in .NET

When I started developing with .NET, Newtonsoft.Json (Json.NET) was the de facto standard. It was everywhere — from small projects to large enterprise applications. Microsoft even used it as the default JSON serializer in ASP.NET Web API and ASP.NET Core (until version 3.0*). But with the introduction of System.Text.Json in .NET Core 3.0, everything changed!

In 2023, I was leading a team working on a high-traffic microservices application processing millions of JSON messages daily and we were using Newtonsoft.Json because, well, that’s what we’d always used. right? But we started noticing memory pressure issues during peak loads. This led us to go down the path that eventually resulted in a migration to System.Text.Json

Performance Difference

After using both libraries, let me break down why System.Text.Json often performs better in a way that makes sense for developers at all levels.

The Speed Difference

JSON processing is like moving boxes (data) from a delivery truck (JSON string) into a warehouse (your application). Here’s how each library handles this:

Newtonsoft.Json (The Traditional Approach)

public class Customer
{
    public string Name { get; set; }
    public string Email { get; set; }
}

string jsonData = @"{
    'name': 'John Doe',
    'email': 'john@example.com'
}";

var customer = JsonConvert.DeserializeObject(jsonData);

What happens behind the scenes:

• Creates temporary string copies of the data
• Allocates memory multiple times during processing
• Needs to convert between different string formats

It’s like unpacking the delivery truck, putting everything in a temporary storage area (or in a ground), then moving it to its final location — more steps — more time — more resources!!

System.Text.Json (The Modern Approach)

using var jsonDocument = JsonDocument.Parse(jsonData);
var root = jsonDocument.RootElement;

var customer = new Customer
{
    Name = root.GetProperty("name").GetString(),
    Email = root.GetProperty("email").GetString()
};

What happens behind the scenes:

• Works directly with the raw JSON data
• Minimizes temporary copies
• Processes data more efficiently in its original format

It’s like having a direct conveyor belt from the truck to the exact shelf in the warehouse — fewer steps, faster delivery.

Impact on the Project!

General example. let’s say we have an e-commerce project, we process thousands of orders per minute. Here’s what we saw

— Small Payload (Single Order — 1KB)

• Newtonsoft.Json: 0.1ms
• System.Text.Json: 0.06ms
• Difference: Not noticeable for single operations

— Large Payload (Batch of 10,000 Orders — 10MB)

• Newtonsoft.Json: 850ms
• System.Text.Json: 520ms
• Difference: Very noticeable in batch processing

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you must be thinking! if a library exists then there must be a use-case! right? uhm you are correct here’s how you can use it efficiently!

When to Use Each Library!

Choose System.Text.Json When:

• Building new .NET Core/5+ applications
• Processing large amounts of data
• Working with microservices
• Need maximum performance
• Dealing with simple, well-defined data structures

// Efficient batch processing
public async Task ProcessOrderBatch(string[] orderJsons)
{
    var options = new JsonSerializerOptions
    {
        PropertyNameCaseInsensitive = true
    }; //part of a life for me..lol

    foreach (var json in orderJsons)
    {
        var order = JsonSerializer.Deserialize(json, options);
        await ProcessOrder(order);
    }
}

Stick with Newtonsoft.Json When:

• Working with legacy .NET applications
• Need complex JSON manipulation
• Using dynamic JSON structures
• Require specific JSON.NET features
• Have existing code heavily dependent on Newtonsoft.Json

// Example of dynamic JSON handling
public void ProcessDynamicData(string json)
{
    dynamic data = JObject.Parse(json);
    if (data.type == "special")
    {
        Console.WriteLine($"Found special data: {data.value}");
    }
}

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My Opinions if it matters!

1. Data Handling

// System.Text.Json
var options = new JsonSerializerOptions
{
    // Use this for consistent date formatting
    DateTimeNamingPolicy = JsonNamingPolicy.CamelCase,
    PropertyNamingPolicy = JsonNamingPolicy.CamelCase
};

// Newtonsoft.Json
var settings = new JsonSerializerSettings
{
    DateFormatHandling = DateFormatHandling.IsoDateFormat
};

2. Case Sensitivity

// System.Text.Json
var options = new JsonSerializerOptions
{
    PropertyNameCaseInsensitive = true  // Make it case insensitive
};

// Newtonsoft.Json
var settings = new JsonSerializerSettings
{
    ContractResolver = new CamelCasePropertyNamesContractResolver()
};

3. Best Practices

here are some crucial best practices:

1. Configuration Management

Always centralize your JSON serialization configuration!

example:

public static class JsonConfig
{
    public static readonly JsonSerializerOptions DefaultOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        WriteIndented = false,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
        NumberHandling = JsonNumberHandling.AllowReadingFromString,
        Converters =
        {
            new JsonStringEnumConverter(JsonNamingPolicy.CamelCase),
            new HighPerformanceDateConverter(),
        }
    };

    public static readonly JsonSerializerOptions ApiOptions = new(DefaultOptions)
    {
        WriteIndented = true,
        Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
    };
}

2. Error Handling Strategies

One area where almost all developers stumble is error handling!

example:

public class JsonHelper
{
    public static T DeserializeWithFallback(string json, T defaultValue = default)
    {
        try
        {
            return JsonSerializer.Deserialize(json, JsonConfig.DefaultOptions);
        }
        catch (JsonException ex)
        {
            // Log the error with context
            _logger.LogError(ex, "JSON Deserialization failed for type {Type}. Content: {Json}", 
                typeof(T).Name, json.Length > 100 ? json[..100] + "..." : json);
                
            return defaultValue;
        }
    }
}

4. Making the Switch

If you’re considering moving from Newtonsoft.Json to System.Text.Json:

Start Small

// Begin with simple DTOs
public class SimpleOrder
{
    public string OrderId { get; set; }
    public decimal Amount { get; set; }
}

// Test both serializers
var order = new SimpleOrder { OrderId = "12345", Amount = 99.99m };

// Old way
var oldJson = JsonConvert.SerializeObject(order);

// New way
var newJson = JsonSerializer.Serialize(order);

// Compare results
Console.WriteLine(oldJson == newJson); // Should be true

Gradual Migration

• Start with new features
• Test thoroughly
• Keep both libraries during the transition
• Document any behavioral differences

Conclusion

After working with both libraries, I’ve learned that there’s no one-size-fits-all solution. The choice between Newtonsoft.Json and System.Text.Json should be based on your specific needs, team expertise, and project constraints!

My preference for new projects! I lean towards System.Text.Json for its performance benefits and modern design. However, I maintain a healthy respect for Newtonsoft.Json’s rich feature set and handling dynamic cases ecosystem.

The best tool isn’t always the fastest one — it’s the one that best fits your project’s needs and your team’s expertise

Those who wanna say Thanks | Buy me a Coffee🖤

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Author’s Corner:

A senior .NET developer with years of experience in financial and AI applications, specializing in high-performance distributed systems and Blazor applications.

#dotnet #optimization #serialization #newtonsoft #microsoft