Today we are talking about Migrating from Newtonsoft.Json to System.Text.Json in .NET 8 can improve performance, reduce dependencies, and enhance security. However, the transition requires careful handling due to differences between the two libraries. This guide walks you through the key differences, migration steps, challenges, and solutions to help ensure a smooth migration.

Migrating from Newtonsoft.Json?
Before we dive into migration steps, let's briefly explore why you should consider moving to `System.Text.Json`:
Performance: `System.Text.Json` is optimized for speed and memory efficiency.
Security: It offers stricter character escaping to prevent injection attacks.
Built-in Support: `System.Text.Json` is the default serializer in ASP.NET Core and .NET 8.
Reduced Dependencies: Unlike `Newtonsoft.Json`, no external package installation is required.
Key Differences Between Newtonsoft.Json and System.Text.Json
1. Case Sensitivity
`System.Text.Json` is case-sensitive by default, whereas `Newtonsoft.Json` is case-insensitive.
Solution: Enable case-insensitive deserialization using `PropertyNameCaseInsensitive = true`.
2. Property Naming Policy
`System.Text.Json` uses camelCase by default.
Solution: Explicitly define property names using `[JsonPropertyName]` attributes.
3. Character Escaping
`System.Text.Json` escapes characters differently to improve security.
Solution: Test your output and update clients if necessary.
4. Comments & Trailing Commas
`System.Text.Json` does not support JSON comments and trailing commas by default.
Solution: Enable them with `JsonCommentHandling.Skip` and `AllowTrailingCommas = true`.
5. Custom Converters
The approach for writing custom converters differs between the two libraries.
Migration Steps
Step 1: Remove Newtonsoft.Json Dependency
If your project references `Newtonsoft.Json`, remove it:
dotnet remove package Newtonsoft.Json
Step 2: Update Serialization Attributes
Replace `Newtonsoft.Json` attributes with `System.Text.Json` equivalents.
Before (Newtonsoft.Json):
using Newtonsoft.Json;
public class Product
{
[JsonProperty("product_id")]
public int Id { get; set; }
[JsonProperty("product_name")]
public string Name { get; set; }
}
After (System.Text.Json):
using System.Text.Json.Serialization;
public class Product
{
[JsonPropertyName("product_id")]
public int Id { get; set; }
[JsonPropertyName("product_name")]
public string Name { get; set; }
}
Step 3: Configure JsonSerializerOptions
Set up serialization options for expected behaviour:
var options = new JsonSerializerOptions
{
PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
PropertyNameCaseInsensitive = true,
WriteIndented = true,
AllowTrailingCommas = true,
ReadCommentHandling = JsonCommentHandling.Skip
};
Step 4: Handle Enum Serialization
By default, `System.Text.Json` serializes enums as integers. To serialize them as strings:
[JsonConverter(typeof(JsonStringEnumConverter))]
public enum UserRole
{
Administrator,
StandardUser,
GuestAccount
}
If enum values differ from their property names, create a custom converter:
public class UserRoleConverter : JsonConverter<UserRole>
{
public override UserRole Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
string value = reader.GetString();
return value switch
{
"administrator" => UserRole.Administrator,
"standard_user" => UserRole.StandardUser,
"guest_account" => UserRole.GuestAccount,
_ => throw new JsonException($"Unknown UserRole: {value}")
};
}
public override void Write(Utf8JsonWriter writer, UserRole value, JsonSerializerOptions options)
{
string stringValue = value switch
{
UserRole.Administrator => "administrator",
UserRole.StandardUser => "standard_user",
UserRole.GuestAccount => "guest_account",
_ => throw new JsonException($"Unknown UserRole: {value}")
};
writer.WriteStringValue(stringValue);
}
}
Step 5: Implement Custom Converters
For types requiring special handling, implement a custom converter.
Example: Custom DateTime Converter
public class DateTimeConverter : JsonConverter<DateTime>
{
private const string Format = "yyyy-MM-dd";
public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
return DateTime.ParseExact(reader.GetString(), Format, CultureInfo.InvariantCulture);
}
public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
{
writer.WriteStringValue(value.ToString(Format));
}
}
Register the converter:
var options = new JsonSerializerOptions();
options.Converters.Add(new DateTimeConverter());
Step 6: Test Thoroughly
After migration, test your application thoroughly to ensure serialization and deserialization work as expected.
Common Challenges and Solutions
Challenge | Solution |
Case sensitivity issues | Enable PropertyNameCaseInsensitive = true |
Enum serialization differences | Use JsonStringEnumConverter or a custom converter |
Newtonsoft features missing | Implement custom converters for missing functionalities |
Performance optimization | Reuse JsonSerializerOptions instances to improve performance |
Pros and Cons of System.Text.Json
✅ Pros
Performance: Faster and more memory-efficient than `Newtonsoft.Json`.
Security: Provides better character escaping for XSS protection.
Integrated: Comes built into .NET, reducing external dependencies.
❌ Cons
Fewer features: Some features in `Newtonsoft.Json` (e.g., `JObject`, LINQ to JSON) are not directly available.
Stricter parsing: Does not support comments or trailing commas by default.
Final Thoughts
Migrating to `System.Text.Json` in .NET 8 is a worthwhile effort for performance and security improvements. While it requires careful adjustments, following the outlined steps and addressing common challenges can make the transition smooth. Test thoroughly, implement custom converters where needed, and enjoy the benefits of a more efficient JSON serialization library!
Have you started migrating? Share your experiences and challenges!
Comments