fix: properly marshal ToolAnnotations with false values (#260)

Author: pottekkat

client/inprocess_test.go

@@ -22,13 +22,11 @@ func TestInProcessMCPClient(t *testing.T) {
 		"test-tool",
 		mcp.WithDescription("Test tool"),
 		mcp.WithString("parameter-1", mcp.Description("A string tool parameter")),
-		mcp.WithToolAnnotation(mcp.ToolAnnotation{
-			Title:           "Test Tool Annotation Title",
-			ReadOnlyHint:    true,
-			DestructiveHint: false,
-			IdempotentHint:  true,
-			OpenWorldHint:   false,
-		}),
+		mcp.WithTitleAnnotation("Test Tool Annotation Title"),
+		mcp.WithReadOnlyHintAnnotation(true),
+		mcp.WithDestructiveHintAnnotation(false),
+		mcp.WithIdempotentHintAnnotation(true),
+		mcp.WithOpenWorldHintAnnotation(false),
 	), func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
 		return &mcp.CallToolResult{
 			Content: []mcp.Content{
@@ -143,10 +141,10 @@ func TestInProcessMCPClient(t *testing.T) {
 		}
 		testToolAnnotations := (*toolListResult).Tools[0].Annotations
 		if testToolAnnotations.Title != "Test Tool Annotation Title" ||
-			testToolAnnotations.ReadOnlyHint != true ||
-			testToolAnnotations.DestructiveHint != false ||
-			testToolAnnotations.IdempotentHint != true ||
-			testToolAnnotations.OpenWorldHint != false {
+			*testToolAnnotations.ReadOnlyHint != true ||
+			*testToolAnnotations.DestructiveHint != false ||
+			*testToolAnnotations.IdempotentHint != true ||
+			*testToolAnnotations.OpenWorldHint != false {
 			t.Errorf("The annotations of the tools are invalid")
 		}
 	})

client/sse_test.go

@@ -2,10 +2,11 @@ package client
 
 import (
 	"context"
-	"github.com/mark3labs/mcp-go/client/transport"
 	"testing"
 	"time"
 
+	"github.com/mark3labs/mcp-go/client/transport"
+
 	"github.com/mark3labs/mcp-go/mcp"
 	"github.com/mark3labs/mcp-go/server"
 )
@@ -25,13 +26,11 @@ func TestSSEMCPClient(t *testing.T) {
 		"test-tool",
 		mcp.WithDescription("Test tool"),
 		mcp.WithString("parameter-1", mcp.Description("A string tool parameter")),
-		mcp.WithToolAnnotation(mcp.ToolAnnotation{
-			Title:           "Test Tool Annotation Title",
-			ReadOnlyHint:    true,
-			DestructiveHint: false,
-			IdempotentHint:  true,
-			OpenWorldHint:   false,
-		}),
+		mcp.WithTitleAnnotation("Test Tool Annotation Title"),
+		mcp.WithReadOnlyHintAnnotation(true),
+		mcp.WithDestructiveHintAnnotation(false),
+		mcp.WithIdempotentHintAnnotation(true),
+		mcp.WithOpenWorldHintAnnotation(false),
 	), func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
 		return &mcp.CallToolResult{
 			Content: []mcp.Content{
@@ -111,10 +110,10 @@ func TestSSEMCPClient(t *testing.T) {
 		}
 		testToolAnnotations := (*toolListResult).Tools[0].Annotations
 		if testToolAnnotations.Title != "Test Tool Annotation Title" ||
-			testToolAnnotations.ReadOnlyHint != true ||
-			testToolAnnotations.DestructiveHint != false ||
-			testToolAnnotations.IdempotentHint != true ||
-			testToolAnnotations.OpenWorldHint != false {
+			*testToolAnnotations.ReadOnlyHint != true ||
+			*testToolAnnotations.DestructiveHint != false ||
+			*testToolAnnotations.IdempotentHint != true ||
+			*testToolAnnotations.OpenWorldHint != false {
 			t.Errorf("The annotations of the tools are invalid")
 		}
 	})

mcp/tools.go

@@ -139,13 +139,13 @@ type ToolAnnotation struct {
 	// Human-readable title for the tool
 	Title string `json:"title,omitempty"`
 	// If true, the tool does not modify its environment
-	ReadOnlyHint bool `json:"readOnlyHint,omitempty"`
+	ReadOnlyHint *bool `json:"readOnlyHint,omitempty"`
 	// If true, the tool may perform destructive updates
-	DestructiveHint bool `json:"destructiveHint,omitempty"`
+	DestructiveHint *bool `json:"destructiveHint,omitempty"`
 	// If true, repeated calls with same args have no additional effect
-	IdempotentHint bool `json:"idempotentHint,omitempty"`
+	IdempotentHint *bool `json:"idempotentHint,omitempty"`
 	// If true, tool interacts with external entities
-	OpenWorldHint bool `json:"openWorldHint,omitempty"`
+	OpenWorldHint *bool `json:"openWorldHint,omitempty"`
 }
 
 // ToolOption is a function that configures a Tool.
@@ -173,10 +173,10 @@ func NewTool(name string, opts ...ToolOption) Tool {
 		},
 		Annotations: ToolAnnotation{
 			Title:           "",
-			ReadOnlyHint:    false,
-			DestructiveHint: true,
-			IdempotentHint:  false,
-			OpenWorldHint:   true,
+			ReadOnlyHint:    ToBoolPtr(false),
+			DestructiveHint: ToBoolPtr(true),
+			IdempotentHint:  ToBoolPtr(false),
+			OpenWorldHint:   ToBoolPtr(true),
 		},
 	}
 
@@ -212,12 +212,53 @@ func WithDescription(description string) ToolOption {
 	}
 }
 
+// WithToolAnnotation adds optional hints about the Tool.
 func WithToolAnnotation(annotation ToolAnnotation) ToolOption {
 	return func(t *Tool) {
 		t.Annotations = annotation
 	}
 }
 
+// WithTitleAnnotation sets the Title field of the Tool's Annotations.
+// It provides a human-readable title for the tool.
+func WithTitleAnnotation(title string) ToolOption {
+	return func(t *Tool) {
+		t.Annotations.Title = title
+	}
+}
+
+// WithReadOnlyHintAnnotation sets the ReadOnlyHint field of the Tool's Annotations.
+// If true, it indicates the tool does not modify its environment.
+func WithReadOnlyHintAnnotation(value bool) ToolOption {
+	return func(t *Tool) {
+		t.Annotations.ReadOnlyHint = &value
+	}
+}
+
+// WithDestructiveHintAnnotation sets the DestructiveHint field of the Tool's Annotations.
+// If true, it indicates the tool may perform destructive updates.
+func WithDestructiveHintAnnotation(value bool) ToolOption {
+	return func(t *Tool) {
+		t.Annotations.DestructiveHint = &value
+	}
+}
+
+// WithIdempotentHintAnnotation sets the IdempotentHint field of the Tool's Annotations.
+// If true, it indicates repeated calls with the same arguments have no additional effect.
+func WithIdempotentHintAnnotation(value bool) ToolOption {
+	return func(t *Tool) {
+		t.Annotations.IdempotentHint = &value
+	}
+}
+
+// WithOpenWorldHintAnnotation sets the OpenWorldHint field of the Tool's Annotations.
+// If true, it indicates the tool interacts with external entities.
+func WithOpenWorldHintAnnotation(value bool) ToolOption {
+	return func(t *Tool) {
+		t.Annotations.OpenWorldHint = &value
+	}
+}
+
 //
 // Common Property Options
 //

mcp/utils.go

@@ -775,3 +775,8 @@ func ParseStringMap(request CallToolRequest, key string, defaultValue map[string
 	v := ParseArgument(request, key, defaultValue)
 	return cast.ToStringMap(v)
 }
+
+// ToBoolPtr returns a pointer to the given boolean value
+func ToBoolPtr(b bool) *bool {
+	return &b
+}

server/server_test.go

@@ -900,10 +900,10 @@ func TestMCPServer_HandleUndefinedHandlers(t *testing.T) {
 		},
 		Annotations: mcp.ToolAnnotation{
 			Title:           "test-tool",
-			ReadOnlyHint:    true,
-			DestructiveHint: false,
-			IdempotentHint:  false,
-			OpenWorldHint:   false,
+			ReadOnlyHint:    mcp.ToBoolPtr(true),
+			DestructiveHint: mcp.ToBoolPtr(false),
+			IdempotentHint:  mcp.ToBoolPtr(false),
+			OpenWorldHint:   mcp.ToBoolPtr(false),
 		},
 	}, func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
 		return &mcp.CallToolResult{}, nil