How to enable OpenAPI / Swagger UI and customizing it

Short answer: Add Swashbuckle.AspNetCore NuGet package. Configure Swagger services (builder.Services.AddSwaggerGen()). Enable middleware (app.UseSwagger(), app.UseSwaggerUI()). Customize with options like API info, document filters, UI themes.

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.