Why is HttpRepl unable to find an OpenAPI description? The command "ls" does not show available endpoints – Asp.net

In step 5 HttpRepl emits the warning Unable to find an OpenAPI description, which means that it can’t find the swagger endpoint, and therefore the ls command wont work.

I assume you are using VS Code and ASP.NET Core 5.0. Here is my output from running dotnet --version:

5.0.401

If we are using Visual Studio, then remember to enable swagger when you create the project – I am using Visual Studio 2019 to create the screenshot:

Specifying your OpenAPI description

To find out which endpoint to use, open the file Startup.cs and locate the code fragment that contains the text UseSwaggerUI. You should find this block of code:

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
    app.UseSwagger();
    app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "WebAPI v1"));
}

Use the endpoint you find and run the tool like this:

httprepl http://localhost:5000 --openapi /swagger/v1/swagger.json

If you do not find any references to swagger, then see None of the above worked, swagger isn’t installed below, for how to install and configure swagger for your project.

Ignoring your environment

If specifying the Open API endpoint to use doesn’t work, then you are not running your Web API in a development environment. So either use a development environment, or uncomment the if-statement while testing (to setup your environment for development, see Changing your environment below):

//if (env.IsDevelopment())
//{
    app.UseDeveloperExceptionPage();
    app.UseSwagger();
    app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "WebAPI v1"));
//}

Remember to restore the code you uncommented, if any, before you deploy to production.

Changing your environment

The profile your Web API is using, is specified in the file PropertieslaunchSettings.json. Open the file and search for ASPNETCORE_ENVIRONMENT. Then change the instances you find to:

"ASPNETCORE_ENVIRONMENT": "Development"

If this doesn’t work, or the instances were already set to "Development", it means that you are not using any of the profiles specified in your launch settings. If no profile is used, ASPNETCORE_ENVIRONMENT defaults to "Production". When using the dotnet run command, the --launch-profile parameter lets you specify which profile to use:

dotnet run --launch-profile "name_of_profile"

As a last resort you can set the environment variable ASPNETCORE_ENVIRONMENT in the shell you are using, before you run the command dotnet run:

Bash

export ASPNETCORE_ENVIRONMENT=Development

CMD

set ASPNETCORE_ENVIRONMENT=Development

PowerShell

$env:ASPNETCORE_ENVIRONMENT='Development'

Then run the application without a profile :

dotnet run --no-launch-profile

The default ports, when running without a profile, should be 5000 or 5001. But read the output from the command, to see which ports it assigns to your Web API.

Please note, if you use VS Code to run your project, that VS Code may also have created launch settings in the .vscodelaunch.json. It depends on how you have configured VS Code and what you allow it to do. I found some older articles, that claim that some extensions for VS Code, may interfere with the launch settings, but they didn’t specify which ones.

None of the above worked, swagger isn’t installed

I none of the above worked, it means you don’t have swagger installed. Install swagger for your project and when done, try again.

Package Installation

Open your project in VS Code and run the following command from the Integrated Terminal and replace WebAPI.csproj with the name of your own project file:

dotnet add WebAPI.csproj package Swashbuckle.AspNetCore -v 5.6.3

You can of course run the command from outside VS Code, with your project folder as the current working directory.

Add and configure Swagger middleware

Add the Swagger generator to the services collection in the Startup.ConfigureServices method, as the last statement in the method:

public void ConfigureServices(IServiceCollection services)
{
    [... other code here ...]

    // Register the Swagger generator, defining 1 or more Swagger documents
    services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new OpenApiInfo { Title = "WebAPI", Version = "v1" });
    });

}

In the Startup.Configure method, enable the middleware for serving the generated JSON document and the Swagger UI, at the top of the method:

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");
    });

    [... other code here for setting up routing and the like ...]
}

To learn more about setting up swagger, profiles and the environment

Get started with Swashbuckle and ASP.NET Core
Managing Production and Development Settings in ASP.NET Core
Use multiple environments in ASP.NET Core
ASP.NET Core web API documentation with Swagger / OpenAPI