Note on migrating Web API controllers from ASP.NET 4.x to ASP.NET Core: JSON object casing changes by default

When migrating Web API controllers from ASP.NET 4.x to ASP.NET Core, you may notice that JSON property casing changes by default. ASP.NET 4.x used PascalCase for serialized object properties; ASP.NET Core's default JSON serializer (based on Newtonsoft.Json) switched to camelCase.

Here's an example of how the results look like:

// ASP.NET 4.x
public class Product {
    public string ProductName { get; set; }
}

// JSON output:
{ "ProductName": "Keyboard" }

// ASP.NET Core default
{ "productName": "Keyboard" }

This can surprise client applications expecting the old casing. To restore the previous behavior, configure JSON options in Startup.cs:

services.AddMvc()
    .AddJsonOptions(options =>
    {
        options.SerializerSettings.ContractResolver =
            new DefaultContractResolver();
    });

The above setting restores PascalCase naming. For new APIs, using camelCase is generally preferred because it matches common JavaScript conventions, but for migrated clients, explicit configuration avoids breaking changes.