How can i configure JSON format indents in ASP.NET Core Web API

Question

.NET Core 2.2 and lower:

In your Startup.cs file, call the AddJsonOptions extension:

services.AddMvc()
    .AddJsonOptions(options =>
    {
        options.SerializerSettings.Formatting = Formatting.Indented;
    });

Note that this solution requires Newtonsoft.Json.

.NET Core 3.0 and higher:

In your Startup.cs file, call the AddJsonOptions extension:

services.AddMvc()
    .AddJsonOptions(options =>
    {
        options.JsonSerializerOptions.WriteIndented = true;
    });

As for switching the option based on environment, this answer should help.