`dotnet run` writes the "Using launch settings from ..." message to stdout instead of stderr

[Aethon]

Describe the bug

[On a Mac M1 using .NET 9.]
When using dotnet run to run a project that uses a launchSettings.json file, it writes a startup message like "Using launch settings from {filename}..." to stdout. Other run messages are written (correctly) to stderr. Because the message is written to stdout, it mixes in with the expect output of the program, often making it unparseable.

To Reproduce

1. Clone this simple console project example: https://github.com/Aethon/DotNetOutputExample.
2. Execute dotnet run > output.json.
3. Examine output.json and note that it is not valid JSON due to the message at the top.

Further technical details

The errant line of code is here: https://github.com/dotnet/sdk/blob/main/src/Cli/dotnet/commands/dotnet-run/RunCommand.cs#L135.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[marcpopMSFT]

Triage: This seems reasonable but there is some nuance here as not all tools/customers expect non-errors in stderr even though that is the convention so we haven't rushed to go move everything there. Realistically, we should detect where you're running and decide based on that as some old Powershell versions treat any message to stderr as failures.

[Rohit-78958]

your link is not working

https://github.com/dotnet/sdk/blob/main/src/Cli/dotnet/commands/dotnet-run/RunCommand.cs#L135.

[Aethon]

Oops, the whole dotnet-run tree was moved. Current link: https://github.com/dotnet/sdk/blob/main/src/Cli/dotnet/Commands/Run/RunCommand.cs#L197

[adamburgess]

Hi, when developing MCP servers using the Stdio transport, it is nice to start the project using dotnet run

But, I want to create a server that can be run in Stdio or HTTP transport depending on some options, so I am using launchSettings.json.

Upon startup, vscode complains:

2025-07-31 13:55:52.714 [warning] Failed to parse message: "Using launch settings from [...]\\Properties\\launchSettings.json...\r\n"

It is only a warning so everything still works fine, but it would be nice if I could configure it. The first thing the dotnet MCP guide does is redirect all logger output to stderr, but I cannot control dotnet run.