| title | Logging |
|---|---|
| author | mikekistler |
| description | How to use the logging feature in the MCP C# SDK. |
| uid | logging |
MCP servers can expose log messages to clients through the Logging utility.
This document describes how to implement logging in MCP servers and how clients can consume log messages.
MCP uses the logging levels defined in RFC 5424.
The MCP C# SDK uses the standard .NET ILogger and ILoggerProvider abstractions, which support a slightly different set of logging levels. The following table shows the levels and how they map to standard .NET logging levels.
| Level | .NET | Description | Example Use Case |
|---|---|---|---|
| debug | ✓ | Detailed debugging information | Function entry/exit points |
| info | ✓ | General informational messages | Operation progress updates |
| notice | Normal but significant events | Configuration changes | |
| warning | ✓ | Warning conditions | Deprecated feature usage |
| error | ✓ | Error conditions | Operation failures |
| critical | ✓ | Critical conditions | System component failures |
| alert | Action must be taken immediately | Data corruption detected | |
| emergency | System is unusable |
Note: .NET's ILogger also supports a Trace level (more verbose than Debug) log level.
As there is no equivalent level in the MCP logging levels, Trace level logs messages are silently
dropped when sending messages to the client.
MCP servers that implement the Logging utility must declare this in the capabilities sent in the Initialization phase at the beginning of the MCP session.
Servers built with the C# SDK always declare the logging capability. Doing so does not obligate the server to send log messages—only allows it. Note that stateless MCP servers might not be capable of sending log messages as there might not be an open connection to the client on which the log messages could be sent.
The C# SDK provides an extension method xref:Microsoft.Extensions.DependencyInjection.McpServerBuilderExtensions.WithSetLoggingLevelHandler* on xref:Microsoft.Extensions.DependencyInjection.IMcpServerBuilder to allow the server to perform any special logic it wants to perform when a client sets the logging level. However, the SDK already takes care of setting the xref:ModelContextProtocol.Server.McpServer.LoggingLevel in the xref:ModelContextProtocol.Server.McpServer, so most servers will not need to implement this.
MCP Servers using the MCP C# SDK can obtain an ILoggerProvider from the xref:ModelContextProtocol.Server.McpServer.AsClientLoggerProvider method on xref:ModelContextProtocol.Server.McpServer, and from that can create an ILogger instance for logging messages that should be sent to the MCP client.
When the server indicates that it supports logging, clients should configure the logging level to specify which messages the server should send to the client.
Clients should check if the server supports logging by checking the xref:ModelContextProtocol.Protocol.ServerCapabilities.Logging property of the xref:ModelContextProtocol.Client.McpClient.ServerCapabilities field of xref:ModelContextProtocol.Client.McpClient.
If the server supports logging, the client should set the level of log messages it wishes to receive with the xref:ModelContextProtocol.Client.McpClient.SetLoggingLevelAsync* method on xref:ModelContextProtocol.Client.McpClient. If the client does not set a logging level, the server might choose to send all log messages or none—this is not specified in the protocol. So it's important that the client sets a logging level to ensure it receives the desired log messages and only those messages.
The loggingLevel set by the client is an MCP logging level.
See the Logging Levels section above for the mapping between MCP and .NET logging levels.
Lastly, the client must configure a notification handler for xref:ModelContextProtocol.Protocol.NotificationMethods.LoggingMessageNotification notifications. The following example simply writes the log messages to the console.