how to get value from appsettings.json

appsettings.json

configuration management

.NET Core

application settings

JSON parsing

how to get value from appsettings.json

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C# & .NET

Introduction

In .NET Core and .NET 5+, appsettings.json replaces the older web.config and app.config XML files for application configuration. The framework provides a built-in configuration system that reads appsettings.json at startup and makes values available through dependency injection. You access values using IConfiguration for raw key-value lookups or the strongly-typed Options pattern for structured settings.

The appsettings.json File

json

1{
2  "ConnectionStrings": {
3    "DefaultConnection": "Server=localhost;Database=MyApp;Trusted_Connection=True;"
4  },
5  "Logging": {
6    "LogLevel": {
7      "Default": "Information"
8    }
9  },
10  "AppSettings": {
11    "ApiKey": "abc123",
12    "MaxRetries": 3,
13    "BaseUrl": "https://api.example.com",
14    "Features": {
15      "EnableCaching": true,
16      "CacheDurationMinutes": 30
17    }
18  }
19}

Method 1: IConfiguration (Direct Access)

Inject IConfiguration and read values using section-colon-key notation:

csharp

1public class HomeController : Controller
2{
3    private readonly IConfiguration _config;
4
5    public HomeController(IConfiguration configuration)
6    {
7        _config = configuration;
8    }
9
10    public IActionResult Index()
11    {
12        // Read a simple value
13        string apiKey = _config["AppSettings:ApiKey"];  // "abc123"
14
15        // Read a nested value
16        bool caching = _config.GetValue<bool>("AppSettings:Features:EnableCaching");  // true
17
18        // Read with a default fallback
19        int retries = _config.GetValue<int>("AppSettings:MaxRetries", 5);  // 3
20
21        // Read connection string (shortcut)
22        string connStr = _config.GetConnectionString("DefaultConnection");
23
24        return View();
25    }
26}

The colon : separates nested sections. GetValue<T> handles type conversion automatically.

Method 2: Options Pattern (Recommended)

Bind a configuration section to a strongly-typed class:

csharp

1// 1. Define the settings class
2public class AppSettings
3{
4    public string ApiKey { get; set; }
5    public int MaxRetries { get; set; }
6    public string BaseUrl { get; set; }
7    public FeatureSettings Features { get; set; }
8}
9
10public class FeatureSettings
11{
12    public bool EnableCaching { get; set; }
13    public int CacheDurationMinutes { get; set; }
14}

csharp

// 2. Register in Program.cs (or Startup.cs)
builder.Services.Configure<AppSettings>(
    builder.Configuration.GetSection("AppSettings"));

csharp

1// 3. Inject IOptions<T> in your class
2public class MyService
3{
4    private readonly AppSettings _settings;
5
6    public MyService(IOptions<AppSettings> options)
7    {
8        _settings = options.Value;
9    }
10
11    public void DoWork()
12    {
13        Console.WriteLine(_settings.ApiKey);           // "abc123"
14        Console.WriteLine(_settings.MaxRetries);       // 3
15        Console.WriteLine(_settings.Features.EnableCaching);  // true
16    }
17}

Method 3: Bind to a Class Manually

csharp

1// In Program.cs or a service
2var settings = new AppSettings();
3builder.Configuration.GetSection("AppSettings").Bind(settings);
4
5// Or use Get<T>()
6var settings = builder.Configuration
7    .GetSection("AppSettings")
8    .Get<AppSettings>();

Environment-Specific Settings

.NET automatically loads environment-specific overrides:

appsettings.json                    ← base settings
appsettings.Development.json        ← overrides for Development
appsettings.Production.json         ← overrides for Production

json

1// appsettings.Development.json
2{
3  "AppSettings": {
4    "ApiKey": "dev-key-123",
5    "BaseUrl": "https://dev-api.example.com"
6  }
7}

The environment is determined by the ASPNETCORE_ENVIRONMENT environment variable. Later files override earlier ones — only the keys you specify are overridden, not the entire section.

Reading Arrays

json

{
  "AllowedHosts": ["example.com", "api.example.com", "admin.example.com"]
}

csharp

1// Access by index
2string first = _config["AllowedHosts:0"];  // "example.com"
3
4// Bind to a list
5var hosts = _config.GetSection("AllowedHosts").Get<List<string>>();

IOptionsSnapshot vs IOptionsMonitor

csharp

1// IOptions<T> — singleton, read once at startup
2public MyService(IOptions<AppSettings> options)
3
4// IOptionsSnapshot<T> — scoped, re-reads per request (good for web apps)
5public MyService(IOptionsSnapshot<AppSettings> options)
6
7// IOptionsMonitor<T> — singleton but detects changes via OnChange callback
8public MyService(IOptionsMonitor<AppSettings> monitor)
9{
10    monitor.OnChange(newSettings =>
11    {
12        Console.WriteLine($"Settings changed: {newSettings.ApiKey}");
13    });
14}

Use IOptionsSnapshot when you want updated values per request without restarting. Use IOptionsMonitor for long-running services that need to react to config changes.

Reading in Program.cs (Before DI)

csharp

1var builder = WebApplication.CreateBuilder(args);
2
3// Access configuration before building the app
4string apiKey = builder.Configuration["AppSettings:ApiKey"];
5
6// Or bind to a class
7var settings = builder.Configuration
8    .GetSection("AppSettings")
9    .Get<AppSettings>();

Common Pitfalls

Null values: _config["NonExistent:Key"] returns null, not an exception. Always check for null or use GetValue<T>("key", defaultValue) with a fallback.
Case sensitivity: Configuration keys are case-insensitive in .NET. _config["appsettings:apikey"] works the same as _config["AppSettings:ApiKey"].
Secrets in appsettings.json: Never store passwords or API keys in appsettings.json for production. Use User Secrets (dotnet user-secrets), environment variables, or Azure Key Vault instead.
Forgetting to register Options: IOptions<T> injection fails with a DI error if you forget builder.Services.Configure<T>(section) in Program.cs.
IOptions is singleton: IOptions<T> reads the value once and caches it forever. If you edit appsettings.json at runtime, use IOptionsSnapshot<T> or IOptionsMonitor<T> to pick up changes.

Summary

Use IConfiguration["Section:Key"] for quick, one-off value access
Use the Options pattern (IOptions<T>) for structured, type-safe settings
Connection strings have a shortcut: _config.GetConnectionString("Name")
Environment-specific files (appsettings.{Environment}.json) override base settings automatically
Use IOptionsSnapshot<T> for per-request reload or IOptionsMonitor<T> for change notifications
Never store secrets in appsettings.json — use User Secrets or environment variables

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Data Structures & Algorithms practice on Codemia

Step through 300+ coding interview problems with animated visualisers that show the data structure changing as the code runs. The Blind 75 are free.

Practice algorithms

how to get value from appsettings.json

Data Structures & Algorithms practice on Codemia

Introduction

The appsettings.json File

Method 1: IConfiguration (Direct Access)

Method 2: Options Pattern (Recommended)

Method 3: Bind to a Class Manually

Environment-Specific Settings

Reading Arrays

IOptionsSnapshot vs IOptionsMonitor

Reading in Program.cs (Before DI)

Common Pitfalls

Summary

Related reading

OOD Fundamentals

Data Structures & Algorithms practice on Codemia