Do you check your API serialisation format?

Most REST APIs serialise/deserialise to and from JSON format. To perform this serialisation, a .NET web application typically relies on either Newtonsoft.Json or System.Text.Json.

Modern .NET applications prefer System.Text.Json over Newtonsoft.Json - which is commonly found in earlier versions of .NET and .NET Framework projects. This, however, may break in certain usages.

This issue needs to be addressed when migrating projects from .NET Framework to modern .NET. The primary reason for switching to System.Text.Json is its faster performance and lower memory usage compared to Newtonsoft.Json. However, it also breaks compatibility and lacks some features found in Newtonsoft.Json.

The differences

This Microsoft documentation contains a compiled list of differences between System.Text.Json and Newtonsoft.Json.

Notable Things to Check

• ⚠️ Default Serialisation Property Name Casing
  Since .NET Core 3.0, the default behaviour for JSON property name serialisation has switched to camelCase, whereas earlier versions followed the class's property names as-is (usually in PascalCase). Couple of options to address this when migrating controllers from legacy endpoints while maintaining compatibility:
  • Option A: Implement a per-controller override for migrated legacy APIs to maintain the same behaviour by setting JsonSerializerOptions.PropertyNamingPolicy = null, e.g., via a custom attribute using ActionFilterAttribute.
  • Option B: Apply a global JSON serialisation override to retain JsonSerializerOptions.PropertyNamingPolicy = null.
• ⚠️ No Support for JSON Patch Documents
  Deserialisation of JSON Patch documents might fail due to lack of support for JSON Path queries, e.g., commonly used in legacy PATCH endpoints.
• ⚠️ Limited OData Support
  OData might not work as expected when using System.Text.Json. See more: Example issues.
• ⚠️ Limited Support for Date Formats
  While System.Text.Json supports the ISO 8601-1:2019 format for date and time components, Newtonsoft.Json accommodates a broader range of date-time strings. For example, System.Text.Json cannot deserialise the format 8:00am February, 24 2024.