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Message no longer duplicated in Console log output

When logging to the console using the JSON formatter, log messages are no longer duplicated in the log output. Previously, messages typically appeared three times: once as the top-level Message, again within the State object, and a third time as the original format string.

Version introduced

.NET 10 Preview 7

Previous behavior

Previously, when using a console logger configured with the JSON formatter, log messages were duplicated in the output. For example, the code logger.LogInformation("This is an information message."); produced the following output:

{
  "EventId": 0,
  "LogLevel": "Information",
  "Category": "Program",
  "Message": "This is an information message.",
  "State": {
    "Message": "This is an information message.",
    "{OriginalFormat}": "This is an information message."
  }
}

As you can see, Message appears twice: once as the top-level Message and again inside the State object.

New behavior

Starting in .NET 10, Message appears only at the top level and not inside the State object (typically). The log output looks like this:

{
  "EventId": 0,
  "LogLevel": "Information",
  "Category": "Program",
  "Message": "This is an information message.",
  "State": {
    "{OriginalFormat}": "This is an information message."
  }
}

Type of breaking change

This is a behavioral change.

Reason for change

The goal of this change is to reduce unnecessary logging overhead by eliminating duplicate content. By avoiding repeated formatting of the same message, the change helps:

  • Minimize log output size.
  • Reduce confusion caused by redundant information.
  • Improve performance by preventing multiple formatting operations for the same message.

Overall, this results in cleaner, more efficient, and easier-to-read logs.

If you previously parsed the logging output to extract the Message from within the State object, it's safe to use the top-level Message instead, now that duplication has been removed.

Note

In some cases, a Message might still appear within the State object. This typically happens when its content differs from the top-level Message.

Affected APIs