Difference between Use, Run, Map?

In .NET Core Middleware pipeline, Use, Run, and Map control how request flows through middleware.

Think of them like traffic controllers 🚦

1. Use() — Continue to Next Middleware

Use() can call next middleware in pipeline.

Example

app.Use(async (context, next) =>
{
    Console.WriteLine("Middleware 1 - Before");

    await next();

    Console.WriteLine("Middleware 1 - After");
});

app.Use(async (context, next) =>
{
    Console.WriteLine("Middleware 2");

    await next();
});

Output

Middleware 1 - Before
Middleware 2
Middleware 1 - After

Key Points

✅ Can call next middleware
✅ Can modify request/response
✅ Most commonly used

2. Run() — Terminates Pipeline

Run() does NOT call next middleware
It ends the pipeline immediately 🛑

Example

app.Use(async (context, next) =>
{
    Console.WriteLine("Middleware 1");
    await next();
});

app.Run(async context =>
{
    Console.WriteLine("Middleware 2 - Run");
});

Output

Middleware 1
Middleware 2 - Run

If you add middleware after Run():

app.Run(async context =>
{
    Console.WriteLine("Run Middleware");
});

app.Use(async (context, next) =>
{
    Console.WriteLine("This will never execute");
});

❌ This middleware will never execute

3. Map() — Branch the Pipeline

Map() creates a separate pipeline based on URL path 🔀

Example

app.Map("/admin", adminApp =>
{
    adminApp.Run(async context =>
    {
        await context.Response.WriteAsync("Admin Page");
    });
});

app.Run(async context =>
{
    await context.Response.WriteAsync("Home Page");
});

Results

/admin  → Admin Page
/home   → Home Page

Visual Comparison

Use → Continue pipeline
Run → End pipeline
Map → Branch pipeline

Interview Table (Very Important)

Feature	Use	Run	Map
Calls next middleware	✅ Yes	❌ No	Depends
Ends pipeline	❌ No	✅ Yes	Branch
Creates branch	❌ No	❌ No	✅ Yes
Most common	✅ Yes	❌ No	⚠️ Sometimes

Interview Answer (Short Version)

Use() continues to next middleware.
Run() terminates the pipeline.
Map() creates branch pipeline based on URL path.

Real-world Example

app.UseAuthentication();
app.UseAuthorization();

app.Map("/admin", admin =>
{
    admin.UseAuthorization();
});

app.Run();

Trick Interview Question

Q: Can we place Run() in middle?
👉 Yes, but everything after that won't execute

If you'd like, I can also explain:

UseWhen vs MapWhen (Very common interview question)
Middleware execution order
Real-world production middleware examples