How to add method description in Swagger UI in WebAPI Application

We use additional attributes to add required detail to the swagger documentation:

    [SwaggerOperationSummary("Add a new Pet to the store")]
    [SwaggerImplementationNotes("Adds a new pet using the properties supplied, returns a GUID reference for the pet created.")]
    [Route("pets")]
    [HttpPost]
    public async Task<IHttpActionResult> Post()
    {
        ...
    }

And then in you swagger config make sure to apply these filters:

config.EnableSwagger("swagger",
           c =>
           {
               c.OperationFilter<ApplySwaggerImplementationNotesFilterAttributes>();
               c.OperationFilter<ApplySwaggerOperationSummaryFilterAttributes>();

The code for the filters:

public class ApplySwaggerImplementationNotesFilterAttributes : IOperationFilter
{
    public void Apply(Operation operation, SchemaRegistry schemaRegistry, ApiDescription apiDescription)
    {
        var attr = apiDescription.GetControllerAndActionAttributes<SwaggerImplementationNotesAttribute>().FirstOrDefault();
        if (attr != null)
        {
            operation.description = attr.ImplementationNotes;
        }
    }
}

public class ApplySwaggerOperationSummaryFilterAttributes : IOperationFilter
{
    public void Apply(Operation operation, SchemaRegistry schemaRegistry, ApiDescription apiDescription)
    {
        var attr = apiDescription.GetControllerAndActionAttributes<SwaggerOperationSummaryAttribute>().FirstOrDefault();
        if (attr != null)
        {
            operation.summary = attr.OperationSummary;
        }
    }
}

This is well documented in the project: https://github.com/domaindrivendev/Swashbuckle.AspNetCore#include-descriptions-from-xml-comments

---

Include Descriptions from XML Comments

To enhance the generated docs with human-friendly descriptions, you can annotate controller actions and models with Xml Comments and configure Swashbuckle to incorporate those comments into the outputted Swagger JSON:

1 - Open the Properties dialog for your project, click the "Build" tab and ensure that "XML documentation file" is checked. This will produce a file containing all XML comments at build-time.

At this point, any classes or methods that are NOT annotated with XML comments will trigger a build warning. To suppress this, enter the warning code "1591" into the "Suppress warnings" field in the properties dialog.

2 - Configure Swashbuckle to incorporate the XML comments on file into the generated Swagger JSON:

services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1",
        new Info
        {
            Title = "My API - V1",
            Version = "v1"
        }
     );

     var filePath = Path.Combine(System.AppContext.BaseDirectory, "MyApi.xml");
     c.IncludeXmlComments(filePath);
}

3 - Annotate your actions with summary, remarks and response tags:

/// <summary>
/// Retrieves a specific product by unique id
/// </summary>
/// <remarks>Awesomeness!</remarks>
/// <response code="200">Product created</response>
/// <response code="400">Product has missing/invalid values</response>
/// <response code="500">Oops! Can't create your product right now</response>
[HttpGet("{id}")]
[ProducesResponseType(typeof(Product), 200)]
[ProducesResponseType(typeof(IDictionary<string, string>), 400)]
[ProducesResponseType(500)]
public Product GetById(int id)

4 - You can also annotate types with summary and example tags:

public class Product
{
    /// <summary>
    /// The name of the product
    /// </summary>
    /// <example>Men's basketball shoes</example>
    public string Name { get; set; }

    /// <summary>
    /// Quantity left in stock
    /// </summary>
    /// <example>10</example>
    public int AvailableStock { get; set; }
}

5 - Rebuild your project to update the XML Comments file and navigate to the Swagger JSON endpoint. Note how the descriptions are mapped onto corresponding Swagger fields.

NOTE: You can also provide Swagger Schema descriptions by annotating your API models and their properties with summary tags. If you have multiple XML comments files (e.g. separate libraries for controllers and models), you can invoke the IncludeXmlComments method multiple times and they will all be merged into the outputted Swagger JSON.

---

Following the instructions carefully you should get something that looks like:
https://swashbucklenetcore.azurewebsites.net/swagger/

For ASP.Net Core projects:

1. install nuget package Swashbuckle.AspNetCore.Annotations

2. Use SwaggerOperation attribute for a methods like [SwaggerOperation(Summary = "Write your summary here")]

3. Enable annotations in Startup method ConfigureServices like the following:

   services.AddSwaggerGen(c =>
   {
       c.EnableAnnotations();
       c.SwaggerDoc("v1", new OpenApiInfo { Title = "My API", Version = "v1" });
   });
   

4. To exclude public method from appearing in swagger ui use attribute [ApiExplorerSettings(IgnoreApi = true)]. It is useful cause these methods can break swagger for some reason.

Launch project, go to localhost:[port number]/swagger and enjoy.