All 17 ASP.NET Core Middleware & Request Pipeline questions
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What's the difference between app.Use, app.Run, and app.Map in configuring the middleware pipeline?

Intermediate

Answer

app.Use adds middleware that can call next() to continue the pipeline (non-terminal). app.Run adds terminal middleware that never calls next() -- it always ends the pipeline at that point. app.Map (and MapWhen) branches the pipeline based on a request path or predicate, letting you build entirely separate sub-pipelines for different routes, such as a distinct branch for /admin requests.
app.Map("/admin", adminApp => {
    adminApp.UseMiddleware<AdminAuthMiddleware>();
    adminApp.Run(async context => await context.Response.WriteAsync("Admin area"));
});

app.Run(async context => await context.Response.WriteAsync("Main app"));
Real-world example An application branches its pipeline with app.Map("/health") to serve a lightweight health check response without running through the full authentication and logging middleware stack used by the main application routes.

Common follow-ups: How does MapWhen differ from Map for conditional branching?;Can branched pipelines rejoin the main pipeline afterward?

Health Checks & Readiness/Liveness Probes;Global Exception Handling & Middleware
All 17 ASP.NET Core Middleware & Request Pipeline questions