When will you use this?

You need this before writing any ASP.NET Core code — same as installing Visual Studio before opening a project.

• Every .NET backend job expects you to run dotnet new and dotnet run on day one.
• Interviewers often ask you to explain Program.cs and what Kestrel does.

Real-world: Power BI-style analytics API

The Analytics team building Power BI-style analytics API uses Launch Settings and Configuration to open the right localhost port and Development environment locally. business analysts never see the C# code — they just get a fast, reliable KPI reports and filtered data export.

Production-style code

// Properties/launchSettings.json — applicationUrl
// appsettings.json
{
  "ConnectionStrings": {
    "Default": "Server=.;Database=ShopNest;Trusted_Connection=True;"
  },
  "Logging": { "LogLevel": { "Default": "Information" } }
}

What happens in production: In Power BI-style analytics API, a solid Launch Settings and Configuration foundation lets the team ship KPI reports and filtered data export on schedule without environment surprises.

Lesson example (start here)

Copy this smaller example first. Once it works, compare it with the real-world code above.

// Properties/launchSettings.json — applicationUrl
// appsettings.json
{
  "ConnectionStrings": {
    "Default": "Server=.;Database=ShopNest;Trusted_Connection=True;"
  },
  "Logging": { "LogLevel": { "Default": "Information" } }
}

Line-by-line walkthrough

How it works (big picture)

• launchSettings applies only locally.
• appsettings.Development.json overrides settings when ASPNETCORE_ENVIRONMENT=Development.

Do this on your computer

1. Open launchSettings.json and note the https URL.
2. Run the app and match the browser URL.
3. Add a custom key in appsettings.json and read it in Program.cs with builder.Configuration.
4. Read the real-world section and name which part of the app uses this topic.
5. Run the example locally with dotnet run and confirm the same behavior.
6. Change one value in the example (route, text, or connection string) and predict what will happen before you save.

Experiments — try changing this

• Change a string or route in the example and save — watch the browser or Swagger response update.
• Break the code on purpose (remove a semicolon), read the error message, then fix it.

Remember

launchSettings = local URLs and profiles. appsettings = configuration per environment. Never commit real passwords.

Common questions