WritingTools

Writing tools

한국어

Add AgentMcpToolset to the dependencies of an editor module, then declare static functions on a UAgentMcpToolset subclass:

#include "AgentMcpToolset.h"

#include "MyTools.generated.h"

USTRUCT(BlueprintType)
struct FMyGreeting
{
    GENERATED_BODY()

    UPROPERTY()
    FString Message;
};

UCLASS(meta = (McpToolset = "my"))
class UMyTools : public UAgentMcpToolset
{
    GENERATED_BODY()

public:
    UFUNCTION(BlueprintCallable, Category = "My Tools", meta = (AICallable, McpAccess = "Read", BlueprintInternalUseOnly = "true"))
    static FMyGreeting Greet(const FString& Name = TEXT("world"));
};

This becomes the tool my_greet with an optional string argument name.

• Toolset classes are found automatically. Tool names are <McpToolset>_<function name in snake_case>, and comments provide descriptions.
• McpAccess is Read, Write, Destructive or Control; a missing value is treated as Write.
• Keep BlueprintCallable: Unreal Engine 5.5 records C++ default argument values only for Blueprint-callable functions.
• Return a USTRUCT(BlueprintType); its fields become the JSON result.
• Report failures with UE::AgentMcp::RaiseToolError(TEXT("CODE"), TEXT("Message"), TEXT("Hint")).
• Object arguments (UObject*, AActor*, UClass*) accept object paths, and actors also accept labels.
• For work that finishes on a later frame, return UAgentMcpAsyncResult::Create(TimeoutSeconds, PollFunction); only Read and Control tools can do this.
• To return an image, add an FAgentMcpImage field to the result struct.