ASP.NET appsettings.json

last modified April 3, 2025

In this article, we explore the appsettings.json file in ASP.NET 8. This file is the primary way to store configuration settings in modern ASP.NET applications.

ASP.NET provides a flexible configuration system that works with various sources. The appsettings.json file is the default JSON-based configuration file in .NET.

Basic Definition

The appsettings.json file is a JSON configuration file used in ASP.NET Core and .NET applications. It stores application settings in a structured format.

Configuration values in appsettings.json can be accessed throughout the application. The file supports hierarchical data organization through JSON objects and arrays.

ASP.NET automatically loads appsettings.json during application startup. Environment-specific versions like appsettings.Development.json can override settings based on the current environment.

ASP.NET appsettings.json Example

The following example demonstrates how to use appsettings.json in an ASP.NET 8 application with a Web API controller.

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "AppSettings": {
    "ApiKey": "abc123xyz456",
    "MaxItems": 100,
    "FeatureFlags": {
      "EnableNewSearch": true,
      "EnableExperimentalApi": false
    },
    "AllowedOrigins": [
      "https://example.com",
      "https://test.example.com"
    ]
  }
}

This appsettings.json file contains standard logging configuration and custom application settings. The AppSettings section demonstrates various configuration value types.

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllers();

// Bind configuration to a strongly-typed class
builder.Services.Configure<AppSettings>(
    builder.Configuration.GetSection("AppSettings"));

var app = builder.Build();

app.MapControllers();
app.Run();

This Program.cs sets up the application and binds the AppSettings section to a strongly-typed configuration class. The Configure method enables dependency injection of settings.

public class AppSettings
{
    public string ApiKey { get; set; }
    public int MaxItems { get; set; }
    public FeatureFlags FeatureFlags { get; set; }
    public string[] AllowedOrigins { get; set; }
}

public class FeatureFlags
{
    public bool EnableNewSearch { get; set; }
    public bool EnableExperimentalApi { get; set; }
}

This strongly-typed configuration class mirrors the structure of the AppSettings section in appsettings.json. Nested objects are represented as separate classes.

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Options;

[ApiController]
[Route("api/[controller]")]
public class SettingsController : ControllerBase
{
    private readonly AppSettings _settings;

    public SettingsController(IOptions<AppSettings> settings)
    {
        _settings = settings.Value;
    }

    [HttpGet]
    public IActionResult GetSettings()
    {
        return Ok(new
        {
            _settings.ApiKey,
            _settings.MaxItems,
            _settings.FeatureFlags,
            _settings.AllowedOrigins
        });
    }

    [HttpGet("feature-flags")]
    public IActionResult GetFeatureFlags()
    {
        return Ok(_settings.FeatureFlags);
    }
}

This controller demonstrates two ways to access configuration settings. The constructor injects the strongly-typed AppSettings via IOptions<T>.

The first action returns all settings, while the second focuses on feature flags. The IOptions<T> pattern provides type-safe access to configuration values.

The example shows how to organize complex configuration in appsettings.json and access it throughout the application. Strongly-typed configuration improves code safety and maintainability.

Source

Microsoft ASP.NET Configuration Documentation

In this article, we have explored the appsettings.json file in ASP.NET 8. This powerful configuration system supports both simple and complex application settings.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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