appsettingsjson

appsettings.json is a conventional JSON file used by .NET applications, especially ASP.NET Core, to store configuration data at runtime. When an application starts, the built-in configuration system reads the file and exposes its values through the IConfiguration interface. This enables code to access settings using hierarchical keys such as "Logging:LogLevel:Default" or "ConnectionStrings:DefaultConnection".

The file uses standard JSON syntax and supports sections as objects, with nested objects and arrays. For example:

{ "Logging": { "LogLevel": { "Default": "Information", "Microsoft": "Warning" } }, "ConnectionStrings": { "DefaultConnection": "Server=...;Database=...;User Id=...;" } }

In typical projects, there is also environment-specific configuration: appsettings.Development.json, appsettings.Staging.json, appsettings.Production.json. The runtime loads the base file first and then applies overrides from the environment-specific file, environment variables, and command-line arguments, in that order, so later sources win.

To use the values, developers commonly bind a section to a POCO using the Options pattern, for example, services.Configure<MySettings>(Configuration.GetSection("MySettings")), or read values directly from IConfiguration.

Security and deployment notes: appsettings.json is suitable for non-sensitive defaults but should not store secrets in production. Use user secrets during development or a dedicated secret store (environment variables, Azure Key Vault, etc.) for sensitive data.