The Message Log is a way to display logs to the user in editor and in the output log at the same time. The messages display in the Message Log can react to user interaction by integrating Links to Objects, Blueprints, Assets and more. These messages are displayed in the "Message Log" window available at Window -> Developer Tool -> Message Log and are organized into multiple categories. It's mostly useful as a way to provide artists and Level designer with quick feedback on level or asset configurations.

This article explains how to use the Message Log system in order to display messages to the user in the editor.

Terms and Structure

The Message Log system relies mainly on the FMessageLog class and the FMessageLogModule module.

A message is an instance of a FTokenizedMessage created and added in a Message Log category. The target category is defined by the FMessageLog instance used to create each message.

	/** 
	 * The string literal "PIE" is the FName of the 
	 * message log category to put the message into
	 */
	FMessageLog PieLog("PIE")

Messages could be included in a Page. After the declaration of a page, each following message is included in it. Most of the time, creating a new page means the old messages become invisible.

These messages and pages are displayed in the Message Log window in Log Listings. Each listing is associated with a log category and is declared with the FMessageLogModule module. Listings can be configured with the following properties through the FMessageLogInitializationOptions struct

	FMessageLogInitializationOptions()
		: bShowFilters(false)
		, bShowPages(false)
		, bAllowClear(true)
		, bDiscardDuplicates(false)
		, MaxPageCount(20)
		, bShowInLogWindow(true)
		, bScrollToBottom(false)
	{}

Logging with Message Log

In this section, you will discover how to use the Message Log in your code to display rich messages in the editor's Message Log window.

Simple logging

All messages must be created from an instance of FMessageLog. This instance is created by giving the contructor a single FName containing the log category where you want to send your log message.

// You need the following include at the beginning of the file
// Logging/MessageLog.h contains the declaration of FMessageLog
#include "Logging/MessageLog.h" 

//...

// All messages created with this instance will be flushed to the "Play in Editor" log category listing in the Message Log window
FMessageLog PIELogger("PIE");

See "Editor Log Categories" for a full list of the available log categories or "Log Listing creation" to create your own listing

Message Severity

Now, you can send your messages to this category using the Info(), Warning(), PerformanceWarning(), or Error() methods, depending on the severity of the message. All these methods only take a single FText parameter that contains the content of the message to display.

CriticalError() is deprecated as of Unreal Engine 5.1

namespace EMessageSeverity
{
	/** Ordered according to their severity */
	enum Type : int
	{
		CriticalError UE_DEPRECATED(5.1, "CriticalError was removed because it can't trigger an assert at the callsite. Use 'checkf' instead.") = 0,
		Error = 1,
		PerformanceWarning = 2,
		Warning = 3,
		Info = 4,	// Should be last
	};
}

PIELogger.Info(FText::FromString("Informationnal message"));
PIELogger.Warning(FText::FromString("Warning message"));
PIELogger.PerformanceWarning(FText::FromString("Warning message about performace issue"));
PIELogger.Error(FText::FromString("Error message"));

You can also use the Message() method and specify the severity of it with the EMessageSeverity::Type enum.

PIELogger.Message(EMessageSeverity::Type::Warning, FText::FromString("Enum defined Warning message"));

Messages are stored inside the FMessageLog but not flushed to the Message Log system before the instance destruction. You must destroy the instance to send all messages declared with it. It isn't recomanded to keep an instance of FMessageLog too long, keep it simple, just create a new instance in the current scope when you need to log something and let it be destroyed at the end of the scope.

Rich Logging

You can do much more richer logging with Tokenized Messages

Log Listing creation

You can create your own log listing in your Game Module. For the next sections, we assume that your module is called MyModule

1. Import MessageLog module

In your MyModule.Build.cs file (in the root directory of your module), you can add the MessageLog module in the PrivateIncludePathModuleNames list :

// MyModule.Build.cs
namespace UnrealBuildTool.Rules
{
    public class MyModule : ModuleRules
    {
        public MyModule(ReadOnlyTargetRules Target) : base(Target)
        {
            // ...
            PrivateIncludePathModuleNames.AddRange(
                new string[]
                {
                    // ...
                    "MessageLog",
                }
            );
        }
    }
}
 

2. Save your Log Listing

In the class of the module definition, add these required dependencies:

// MyModule.cpp
// (it should be located in your Private directory)
#include "MessageLogInitializationOptions.h"
#include "MessageLogModule.h"

Then use the MessageLogModule to create your Log Listing

// still in MyModule.cpp
// ...
void FMyModule::StartupModule()
{
	// ...
	// create a message log to use in my module
	FMessageLogModule& MessageLogModule = FModuleManager::LoadModuleChecked<FMessageLogModule>("MessageLog");
	FMessageLogInitializationOptions InitOptions;
	InitOptions.bShowPages = true;
	InitOptions.bAllowClear = true;
	InitOptions.bShowFilters = true;
	MessageLogModule.RegisterLogListing("MyModule", NSLOCTEXT("MyModule", "MyModuleLogLabel", "My Module"), InitOptions);
}

And don't forget to unregister the message log when the module is shutdown:

void FMyModule::ShutdownModule()
{
	// ...
	if (FModuleManager::Get().IsModuleLoaded("MessageLog"))
	{
		// unregister message log
		FMessageLogModule& MessageLogModule = FModuleManager::GetModuleChecked<FMessageLogModule>("MessageLog");
		MessageLogModule.UnregisterLogListing("MyModule");
	}
}

3. Use it

And there you go! You can use it everywhere in your module now:

FMessageLog(FName("MyModule")).Error(LOCTEXT("InvalidValue", "This is not a good value!"));

4. See it

Editor Log Categories

Below is an alphabetized list of all Unreal Engine defined log categories and their associated listings in the editor window. Remember that since these may be generated at compile-time or at module startup, some categories may not be visible until their module / plugin is turn on, or until the conditions are met for the category to be created.

Log Category	Log Listing Label	Notes
AnimBlueprintLog	Anim Blueprint Log
AnimNextCompilerResults	AnimNext Compiler Results
AnimToTextureLog	AnimToTexture Log
AssetCheck	Asset Check
AssetReimport	Asset Reimport
AssetTools	Asset Tools
AutomationTestingLog	Automation Testing Log
BlueprintCompiler or [Blueprint GUID]_[Blueprint Name]_CompilerResultsLog	BlueprintCompiler	(A new category can be created for each blueprint compilation, Not shown in the Message Log window)
BlueprintLog	Blueprint Log
BuildAndSubmitErrors	Build and Submit Errors
CompilerResultsLog	Compiler Log	(A new page is created before each compilation)
Concert	Multi-User
ControlRigLog	Control Rig Log
ControlRigPythonLog	Control Rig Python Log	(Reflects the python commands equivalent to user actions with Control Rig. Helps with automation)
EditorErrors	Editor Errors
HLODResults	HLOD Results
IKRetarget_[UniqueID]	IK Retarget Log	(A new log is created for each retarget)
LightingResults	Lighting Results	(A new page is created before and after each new lightning build)
Live Link	LiveLink
LoadErrors	Load Errors
LoadingInsights	Loading Insights
LocalizationService	Localization Service
MapCheck	Map Check
MassEntity	Mass Entity
Model View Viewmodel	Model View Viewmodel
MoviePipelinePIEExecutor	High Quality Media Export
Mutable	Mutable
NetworkingInsights	Networking Insights
PackagingResults	Packaging Results
PackedLevelActor	Packed Level Actor Log
PIE	Play In Editor	(A new page is created before each Play in Editor session)
RigLogicLog	RigLogic Log
SourceControl	Source Control
SlateStyleLog	Slate Style Log
StallLog	Editor Stall Logger
StateTreeCompiler	StateTreeCompiler
LogStereoPanorama	Panoramic Capture Log
StormSyncDrives	Storm Sync Drives
StormSyncImport	Storm Sync Editor
StormSyncNotifications	Storm Sync Notifications
TimingInsights	Timing Insights
TraceAnalysis	Trace Analysis
TranslationEditor	Translation Editor
UnrealInsights	Unreal Insights
UDNParser	UDN Parse Errors	(Not shown in the Message Log window)
USD	USD
LogVirtualization	Asset Virtualization
WidgetEvents	Widget Event Log
WidgetPreviewLog	Widget Preview Log

This table was created based on a search of .RegisterLogListing( in the editor's source code. Last update March 30th, 2025.

See also

• Logging

• Legacy/Logs, Printing Messages To Yourself During Runtime

• Logs, Printing Class Name, Function Name, Line Number