When designing a REST API, we often consider aspects such as security, caching, design patterns, API documentation, and database connectivity, among others. REST API However, we tend to overlook—or care less about—versioning. In this blog, I’ll explain the importance of versioning and share some real-world use cases. Versioning It’s a technique that enables you to manage multiple versions of your API simultaneously. It provides backward compatibility and maintains consistency for customers. Versioning in ASP.NET Core Web API allows multiple versions of the same API to coexist at the same time. It gives the flexibility to introduce changes and updates to the API without breaking the existing client applications. There are many ways to achieve versioning, and there are NuGet packages that make our life easier in achieving versioning. Here, we are going to explain the way of  NuGet package implementation. Implementation Implementation Here, I am going to create a C# based ASP.NET Core Web API in the Visual Studio 2022 IDE. C# ASP.NET Core Web API It generates the default weather forecast controller. Let’s have a look at the sections. weather forecast controller Controller Controller [ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{

    [HttpGet(Name = "GetWeatherForecast")]
    public IEnumerable<WeatherForecast> Get()
    {
        return Enumerable.Range(1, 5).Select(index => new WeatherForecast
        {
            Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            TemperatureC = Random.Shared.Next(-20, 55),
            Summary = Summaries[Random.Shared.Next(Summaries.Length)]
        })
        .ToArray();
    }

    private static readonly string[] Summaries = new[]
    {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
    };

    private readonly ILogger<WeatherForecastController> _logger;

    public WeatherForecastController(ILogger<WeatherForecastController> logger)
    {
        _logger = logger;
    }
} [ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{

    [HttpGet(Name = "GetWeatherForecast")]
    public IEnumerable<WeatherForecast> Get()
    {
        return Enumerable.Range(1, 5).Select(index => new WeatherForecast
        {
            Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            TemperatureC = Random.Shared.Next(-20, 55),
            Summary = Summaries[Random.Shared.Next(Summaries.Length)]
        })
        .ToArray();
    }

    private static readonly string[] Summaries = new[]
    {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
    };

    private readonly ILogger<WeatherForecastController> _logger;

    public WeatherForecastController(ILogger<WeatherForecastController> logger)
    {
        _logger = logger;
    }
} Model Model public class WeatherForecast
{
    public DateOnly Date { get; set; }

    public int TemperatureC { get; set; }

    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

    public string? Summary { get; set; }
} public class WeatherForecast
{
    public DateOnly Date { get; set; }

    public int TemperatureC { get; set; }

    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

    public string? Summary { get; set; }
} Project Properties Project Properties <Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0" />
  </ItemGroup>

</Project> <Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0" />
  </ItemGroup>

</Project> Let’s run the project. It generates API URL: https://localhost:7298/WeatherForecast https://localhost:7298/WeatherForecast Response to the method Let's consider this method deployed in production. The customer started to use this method, and it’s been a month. Now, customers have a requirement to add “city” to that response. How will you add that? How will you add that? You may think of creating another controller or method. Yes, we can do that. How many controllers will you create? Also, how will you design that in a structured way and meeting with SOLID design principles? SOLID Don’t worry. We have versioning. Let’s go for the implementation. versioning Step 1 - Install NuGet package For your note: We had a package “microsoft.aspnetcore.versioning”. but it's deprecated around August 2022. microsoft.aspnetcore.versioning Install packages Asp.Versioning.Mvc
Asp.Versioning.Mvc.ApiExplorer Asp.Versioning.Mvc Asp.Versioning.Mvc Asp.Versioning.Mvc.ApiExplorer Asp.Versioning.Mvc.ApiExplorer You can see that in the project properties after installation. <PackageReference Include=" Asp.Versioning.Mvc" Version="8.1.0" />
<PackageReference Include=" Asp.Versioning.Mvc.ApiExplorer" Version="8.1.0" /> <PackageReference Include=" Asp.Versioning.Mvc" Version="8.1.0" />
<PackageReference Include=" Asp.Versioning.Mvc.ApiExplorer" Version="8.1.0" /> New class model with the city New class model with the city public class CityWeatherForecast
{
    public DateOnly Date { get; set; }

    public int TemperatureC { get; set; }

    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

    public string? Summary { get; set; }

    public string City { get; set; }
} public class CityWeatherForecast
{
    public DateOnly Date { get; set; }

    public int TemperatureC { get; set; }

    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

    public string? Summary { get; set; }

    public string City { get; set; }
} Design the controller with a version mechanism Design the controller with a version mechanism [ApiController]
[Route("api/v{version:apiVersion}/[controller]")]
[ApiVersion("1.0")]
[ApiVersion("2.0")]
public class WeatherForecastController : ControllerBase
{
   private readonly ILogger<WeatherForecastController> _logger;

    public WeatherForecastController(ILogger<WeatherForecastController> logger)
    {
        _logger = logger;
    }

    [HttpGet, MapToApiVersion("1.0")]
    public IEnumerable<WeatherForecast> Get()
    {
        return Enumerable.Range(1, 5).Select(index => new WeatherForecast
        {
            Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            TemperatureC = Random.Shared.Next(-20, 55),
            Summary = Summaries[Random.Shared.Next(Summaries.Length)]
        })
        .ToArray();
    }

    [HttpGet, MapToApiVersion("2.0")]
    public IEnumerable<CityWeatherForecast> GetV2()
    {
        return Enumerable.Range(1, 5).Select(index => new CityWeatherForecast
        {
            Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            TemperatureC = Random.Shared.Next(-20, 55),
            Summary = Summaries[Random.Shared.Next(Summaries.Length)],
            City = Cities[Random.Shared.Next(Cities.Length)]

        })
        .ToArray();
    }
    private static readonly string[] Cities = new[]
    {
        "Dallas", "Boston", "Austin", "Buffalo", "Rochester", "Naperville", "Columbus", "Detroit", "Miami", "Atlanta"
    };

    private static readonly string[] Summaries = new[]
    {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
    };

    
} [ApiController]
[Route("api/v{version:apiVersion}/[controller]")]
[ApiVersion("1.0")]
[ApiVersion("2.0")]
public class WeatherForecastController : ControllerBase
{
   private readonly ILogger<WeatherForecastController> _logger;

    public WeatherForecastController(ILogger<WeatherForecastController> logger)
    {
        _logger = logger;
    }

    [HttpGet, MapToApiVersion("1.0")]
    public IEnumerable<WeatherForecast> Get()
    {
        return Enumerable.Range(1, 5).Select(index => new WeatherForecast
        {
            Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            TemperatureC = Random.Shared.Next(-20, 55),
            Summary = Summaries[Random.Shared.Next(Summaries.Length)]
        })
        .ToArray();
    }

    [HttpGet, MapToApiVersion("2.0")]
    public IEnumerable<CityWeatherForecast> GetV2()
    {
        return Enumerable.Range(1, 5).Select(index => new CityWeatherForecast
        {
            Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            TemperatureC = Random.Shared.Next(-20, 55),
            Summary = Summaries[Random.Shared.Next(Summaries.Length)],
            City = Cities[Random.Shared.Next(Cities.Length)]

        })
        .ToArray();
    }
    private static readonly string[] Cities = new[]
    {
        "Dallas", "Boston", "Austin", "Buffalo", "Rochester", "Naperville", "Columbus", "Detroit", "Miami", "Atlanta"
    };

    private static readonly string[] Summaries = new[]
    {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
    };

    
} Inject API versioning in service collection in programs.cs file programs.cs // Add services to the container.
builder.Services.AddControllers();

builder.Services.AddApiVersioning(options=>
{
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.AssumeDefaultVersionWhenUnspecified=true;
    options.ReportApiVersions=true;
}).AddMvc(); // Add services to the container.
builder.Services.AddControllers();

builder.Services.AddApiVersioning(options=>
{
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.AssumeDefaultVersionWhenUnspecified=true;
    options.ReportApiVersions=true;
}).AddMvc(); Let's test through Postman URL: https://localhost:7298/api/v1/WeatherForecast Postman URL https://localhost:7298/api/v1/WeatherForecast URL: https://localhost:7298/api/v2/WeatherForecast https://localhost:7298/api/v2/WeatherForecast Here you go, we have successfully designed the controller, and it works well with Postman. Let's have a look at Swagger. Swagger We are getting the “Failed to load API definition” error. Yes, it will fail. Because it treats the same path under the controller, and it doesn’t know which one to resolve to. Now the package “Asp.Versioning. Mvc.ApiExplorer“ comes into the picture. Basically, it also allows Swagger to get all the metadata required to find all the version controllers. Asp.Versioning. Mvc.ApiExplorer Let's create a new class “ConfigureSwaggerOptions.cs” to implement “SwaggerGenOptions” ConfigureSwaggerOptions.cs SwaggerGenOptions public class ConfigureSwaggerOptions : IConfigureOptions<SwaggerGenOptions>
{
    private readonly IApiVersionDescriptionProvider _provider;

    public ConfigureSwaggerOptions(IApiVersionDescriptionProvider provider)
    {
        _provider = provider;
    }
       

    public void Configure(SwaggerGenOptions options)
    {
        // Add a Swagger doc for each discovered API version
        foreach (var description in _provider.ApiVersionDescriptions)
        {
            options.SwaggerDoc(description.GroupName, CreateInfoForApiVersion(description));
        }

            
    }
    private static OpenApiInfo CreateInfoForApiVersion(ApiVersionDescription description)
    {
        var info = new OpenApiInfo
        {
            Title = "Versioned API",
            Version = description.ApiVersion.ToString(),
            Description = "A sample API with versioning and Swagger in .NET 8"
                
        };

        if (description.IsDeprecated)
        {
            info.Description += " - This API version has been deprecated.";
        }

        return info;
    }
} public class ConfigureSwaggerOptions : IConfigureOptions<SwaggerGenOptions>
{
    private readonly IApiVersionDescriptionProvider _provider;

    public ConfigureSwaggerOptions(IApiVersionDescriptionProvider provider)
    {
        _provider = provider;
    }
       

    public void Configure(SwaggerGenOptions options)
    {
        // Add a Swagger doc for each discovered API version
        foreach (var description in _provider.ApiVersionDescriptions)
        {
            options.SwaggerDoc(description.GroupName, CreateInfoForApiVersion(description));
        }

            
    }
    private static OpenApiInfo CreateInfoForApiVersion(ApiVersionDescription description)
    {
        var info = new OpenApiInfo
        {
            Title = "Versioned API",
            Version = description.ApiVersion.ToString(),
            Description = "A sample API with versioning and Swagger in .NET 8"
                
        };

        if (description.IsDeprecated)
        {
            info.Description += " - This API version has been deprecated.";
        }

        return info;
    }
} We now have to inject this package into the services collection and also make a few other changes in the Program.cs file. Program.cs Update the APIVersioning section as below APIVersioning builder.Services.AddApiVersioning(options=>
{
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.AssumeDefaultVersionWhenUnspecified=true;
    options.ReportApiVersions=true;
}).AddMvc()
.AddApiExplorer(options =>
{
    options.GroupNameFormat = "'v'VVV"; // e.g., v1, v2
    options.SubstituteApiVersionInUrl = true;
}); ; builder.Services.AddApiVersioning(options=>
{
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.AssumeDefaultVersionWhenUnspecified=true;
    options.ReportApiVersions=true;
}).AddMvc()
.AddApiExplorer(options =>
{
    options.GroupNameFormat = "'v'VVV"; // e.g., v1, v2
    options.SubstituteApiVersionInUrl = true;
}); ; Inject the newly implemented class before building the app and modify the SwaggerUI section as like below. SwaggerUI // Apply custom SwaggerGenOptions extension (implemented below)
builder.Services.ConfigureOptions<ConfigureSwaggerOptions>();
var app = builder.Build();

app.UseSwaggerUI(options =>
{
    foreach (var description in provider.ApiVersionDescriptions)
    {
        options.SwaggerEndpoint(
            $"/swagger/{description.GroupName}/swagger.json",
            $"API {description.GroupName.ToUpperInvariant()}");
    }
} // Apply custom SwaggerGenOptions extension (implemented below)
builder.Services.ConfigureOptions<ConfigureSwaggerOptions>();
var app = builder.Build();

app.UseSwaggerUI(options =>
{
    foreach (var description in provider.ApiVersionDescriptions)
    {
        options.SwaggerEndpoint(
            $"/swagger/{description.GroupName}/swagger.json",
            $"API {description.GroupName.ToUpperInvariant()}");
    }
} Let’s run it. Hurrah! Swagger is loading. Now we have flexibility in the dropdown menu to choose the version. Summary Summary Here, I have covered the latest trend implementation of versioning as we are currently in .NET 8 LTS. .NET 8 LTS .NET 10 is expected to be released in November 2025 and will be designated as a Long-Term Support (LTS) version. .NET 10 November 2025 Hope they may not have a major change on that. I will write a new article if they have. Hope you enjoyed the article! Hope you enjoyed the article!

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How to Implement API Versioning in ASP.NET Core

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