ASP.NET - Using appsettings.json Overrides

Overrides let multiple configuration files layer values on top of each other. The base appsettings.json loads first, and environment-specific files apply changes without repeating everything. This keeps configuration clean and prevents duplication.

Base Configuration Layer
appsettings.json holds default values that apply everywhere. This file usually contains non-sensitive information such as logging, connection placeholders and feature toggles. These values stay active unless another configuration file replaces them.

Environment Override Files
Files such as appsettings.Development.json or appsettings.Production.json contain settings that overwrite the base file. ASP.NET Core loads these automatically according to the environment name. Only changed values need to be included; the rest are inherited from the base file.

Load Order and Priority
Configuration loads in a sequence. appsettings.json loads first, then the environment file, then environment variables, then user secrets if enabled. Later sources always overwrite earlier ones. This makes it easy to override only what is required for a deployment.

Selective Replacement
Overrides can change individual keys instead of replacing the entire section. This makes configuration flexible; developers can flip a single value, like a log level or feature flag, without touching unrelated settings.

Why Overrides Matter
Overrides let one codebase serve many environments safely. Teams can use debug settings locally, stricter rules in production and experimental options in staging without editing source files. This supports reliable deployment pipelines and protects sensitive data.

Example

appsettings.json

{
  "Logging": { "LogLevel": { "Default": "Information" }},
  "FeatureA": { "Enabled": false }
}

appsettings.Development.json

{
  "Logging": { "LogLevel": { "Default": "Debug" }},
  "FeatureA": { "Enabled": true }
}

Program.cs

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => $"FeatureA: {builder.Configuration["FeatureA:Enabled"]}");
app.Run();

Output in Development:

FeatureA: true