ASP.NET  

Understanding the Difference Between Web.config and App.config in .NET Applications

In .NET development, configuration files are essential for defining application behavior, managing database connections, implementing security rules, and customizing runtime settings.

Two of the most important configuration files used by developers are:

  • Web.config — used in ASP.NET Web Applications

  • App.config — used in Desktop, Console, and WPF Applications

Although both serve the purpose of application configuration, they are designed for different environments and have unique roles in how applications are executed and deployed.

What is Web.config?

Web.config is a configuration file used exclusively in ASP.NET web applications. It defines web-specific settings related to authentication, session management, database connectivity, caching, and custom error handling.

🔹 Key Purposes

  • Define database connection strings

  • Configure authentication and security rules

  • Manage sessions and caching

  • Handle custom error pages

  • Specify URL routing and rewriting rules

Example: Web.config

<configuration>
  <connectionStrings>
    <add name="dbConn"
         connectionString="Data Source=SQLSERVER;Initial Catalog=MyDB;User ID=sa;Password=123"
         providerName="System.Data.SqlClient" />
  </connectionStrings>

  <system.web>
    <authentication mode="Forms" />
    <customErrors mode="On" />
    <sessionState timeout="20"/>
  </system.web>
</configuration>

Execution
Web.config is managed by IIS (Internet Information Services) at runtime.
It supports multiple environment-specific files like Web.Debug.config and Web.Release.config.

What is App.config?

App.config is used in desktop-based or service-based applications such as Windows Forms, Console Apps, WPF Apps, and Windows Services. It contains global configuration settings that help customize an application’s behavior without modifying the source code.

🔹 Key Purposes

  • Define API endpoints and database connections

  • Manage logging configurations and file paths

  • Control application-level settings like intervals, retries, or themes

  • Integrate third-party library configurations

Example: App.config

<configuration>
  <appSettings>
    <add key="ApiUrl" value="https://api.myapp.com"/>
    <add key="EmailSupport" value="[email protected]"/>
  </appSettings>

  <connectionStrings>
    <add name="dbConn"
         connectionString="Data Source=SQLSERVER;Initial Catalog=MyDB;Integrated Security=True" />
  </connectionStrings>
</configuration>

Execution

When the project is compiled, App.config is automatically renamed to MyApp.exe.config and placed alongside the executable file in the build directory.

Membership not found