'dotnet swagger tofile' command fails with 'incorrect runtime' error

• .NET
• Swagger
• OpenAPI
• Quickfix

I have come across a rather nasty bug: after a successful build of our ASP.NET 5 app, we generate a swagger file using Swashbuckle.AspNetCore.Cli tool with dotnet swagger tofile command. This is set up as a postbuild event. Unfortunately, it doesn’t work on my machine, but it does work completely fine on my colleague’s machine.

UDPATE (4/20/2024): if you encounter this error with .NET 8 - read my new post addressing this issue.

The post build error I am getting is something like this:

The command "dotnet swagger tofile --output \swagger.json bin\Debug\net5.0\myapi.dll v1 " exited with code -532462766.

The error itself is not too useful, so the next place to check is the build output window. And it helps a bit:

Tool 'swashbuckle.aspnetcore.cli' (version '6.2.3') was restored. Available commands: swagger

Restore was successful.
Unhandled exception. System. IO. FileLoadException: Could not load file or assembly 'System. Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The located assembly's manifest definition does not match the assembly reference. (0x80131040)

But it doesn’t solve our issue. A natural step would be to go and install .NET 6 SDK since it seems it’s missing somehow, but you would see it doesn’t help. In fact, .NET 6 had been installed already, and this is what causes my swagger file generation to fail (and it also explains why it works on another machine - it actually doesn’t have .NET 6 installed).

So the reason is dotnet version mismatch, our project targets ASP.NET 5, but .NET CLI uses the latest SDK by default (in my case it was .NET 6). That is why we get this a bit tricky, but actually meaningful System.Runtime message.

Quickfix

The solution here is to add global.json to your working directory (solution folder will work too):

{
"sdk": {
"version": "5.0.406",
"rollForward": "latestPatch"
}
}

This file will instruct .NET CLI to use version 5.0.406 or a bigger minor version. And now it works! Hopefully, it helps you too.

Useful tips

• check your .config/dotnet-tools.json tools-manifest file, to see which Swashbuckle.AspNetCore.Cli version is used
• try updating Swashbuckle.AspNetCore.Cli to the latest version available
• update all the Swachbuckle nuget packages
• use dotnet --info command to check the .NET CLI version used
• use dotnet --list-sdks to list all installed SDKs
• update your project to the latest .NET version