Day 1 · Step 3 — Swagger

Check up-api/Program.cs first — recent dotnet new webapi templates already scaffold OpenAPI (AddOpenApi() / MapOpenApi()). If Swagger UI specifically is wanted (not just the raw OpenAPI JSON), add Swashbuckle:

cd up-api
dotnet add package Swashbuckle.AspNetCore

In Program.cs:

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
// ...
app.UseSwagger();
app.UseSwaggerUI();