These gists are part of the articles: https://blog.georgekosmidis.net/2020/07/11/get-started-with-swagger-and-asp-net-core/ and https://blog.georgekosmidis.net/2020/07/11/swagger-in-asp-net-core-tips-and-tricks/

Configure_swagger.cs

public void Configure(IApplicationBuilder app)
{
    //...
    
    // Enable middleware to serve generated Swagger as a JSON endpoint.
    app.UseSwagger();

    // Enable middleware to serve swagger-ui (HTML, JS, CSS, etc.),
    // specifying the Swagger JSON endpoint.
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
    });

    //...
}

ConfigureServices_swagger.cs

public void ConfigureServices(IServiceCollection services)
{
    //...

    // Register the Swagger generator, defining 1 or more Swagger documents
    services.AddSwaggerGen();
    
    //...
}

swagger_AddressModel.cs

    /// <summary>
    /// An object that represents an address
    /// </summary>
    public class AddressModel
    {
        /// <summary>
        /// The Street part of the address
        /// </summary>
        [MinLength(1), MaxLength(255)]
        public string Street { get; set; }
        
        /// <summary>
        /// The number of the street
        /// </summary>
        [MinLength(1), MaxLength(35)]
        public string StreetNumber { get; set; }
        
        /// <summary>
        /// The City
        /// </summary>
        [MinLength(3), MaxLength(40)]
        public string City { get; set; }
        
        /// <summary>
        /// The ZIP Code
        /// </summary>
        [MinLength(4), MaxLength(20)]
        public string Zip { get; set; }
        
        /// <summary>
        /// The Country
        /// 
        /// NOTE: This should be the ISO-3166-1 Alpha-2 code for countries (https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2#NL), i.e. NL for Netherlands.
        /// </summary>
        public string Country { get; set; }
    }

Swagger_branding.cs

public void Configure(IApplicationBuilder app)
{
    app.UseStaticFiles();
    
    //...

}

swagger_comments.cs

services.AddSwaggerGen(c =>
{
    // Set the comments path for the Swagger JSON and UI.
    var xmlFile = $"{Assembly.GetExecutingAssembly().GetName().Name}.xml";
    var xmlPath = Path.Combine(AppContext.BaseDirectory, xmlFile);
    c.IncludeXmlComments(xmlPath);
});

swagger_css.cs

app.UseSwaggerUI(c =>
{
     c.InjectStylesheet("/your_path/your_theme.css");
}

swagger_OpenApiInfo.cs

services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1", new OpenApiInfo
    {
        Version = "v1",
        Title = "The .NET Lab API",
        Description = "An imaginary API of my blog",
        TermsOfService = new Uri("https://blog.georgekosmidis.net/privacy-policy/"),
        Contact = new OpenApiContact
        {
            Name = "George Kosmidis",
            Email = string.Empty,
            Url = new Uri("https://georgekosmidis.net"),
        },
        License = new OpenApiLicense
        {
            Name = "Use under MIT",
            Url = new Uri("https://blog.georgekosmidis.net/privacy-policy/"),
        }
    });
});

swagger_responsetypes.cs

/// <summary>
/// Creates a TodoItem.
/// </summary>
/// <remarks>
/// Sample request:
///
///     POST /Todo
///     {
///        "id": 1,
///        "name": "Item1",
///        "isComplete": true
///     }
///
/// </remarks>
/// <param name="item"></param>
/// <returns>A newly created TodoItem</returns>
/// <response code="201">Returns the newly created item</response>            //Describe the response 201
/// <response code="400">If the item is null</response>                       //Describe the response 400           
[HttpPost]
[ProducesResponseType(StatusCodes.Status201Created)]                          //Instruct Swagger about the 201
[ProducesResponseType(StatusCodes.Status400BadRequest)]                       //Instruct Swagger about the 400
public ActionResult<TodoItem> Create(TodoItem item)
{
    _context.TodoItems.Add(item);
    _context.SaveChanges();

    return CreatedAtRoute("GetTodo", new { id = item.Id }, item);
}

swagger_RoutePrefix.cs

app.UseSwaggerUI(c =>
{
    c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
    c.RoutePrefix = string.Empty;
});

swagger_SerializeAsV2.cs

app.UseSwagger(c =>
    {
        c.SerializeAsV2 = true;
    });