1. What is this?
A variable stores a value under a name: string name = "Ava". A route parameter is a placeholder in a URL: /hello/{name} captures whatever comes after /hello/ into name. So visiting /hello/Liam replies Hello, Liam.
2. Why do we use it?
Profiles, products, orders — all are the same page shape with different values. Parameters make one route serve millions of pages.
3. Syntax breakdown
string name = "Ava";
Variable holding text.
app.MapGet("/hello/{name}", (string name) => $"Hello, {name}");{name} captures that URL segment; the handler receives it as parameter name.
Console.WriteLine($"Hello, {name}");Runnable version: interpolation substitutes the variable.
5. Common mistakes
- Mismatching placeholder and parameter names ({name} vs (string user)).
- Forgetting $ before interpolated strings.
- Assuming the URL value has the right type — validate it.
Practice task
Add string city = "Berlin"; and print "Hello, Ava from Berlin." with interpolation.
Hint
$"Hello, {name} from {city}."
Try it below — tests run automatically when you press Run.
Output
Press Run to see output.
Mini quiz
3 questions. Answer, then check.
1. What is a route parameter?
2. What does $"...{x}..." do?
3. Why validate route values?