diff --git a/api/types.go b/api/types.go
index 4f2fb9c93..1615fce6f 100644
--- a/api/types.go
+++ b/api/types.go
@@ -323,7 +323,7 @@ type ToolFunctionParameters struct {
 	Type       string                  `json:"type"`
 	Defs       any                     `json:"$defs,omitempty"`
 	Items      any                     `json:"items,omitempty"`
-	Required   []string                `json:"required"`
+	Required   []string                `json:"required,omitempty"`
 	Properties map[string]ToolProperty `json:"properties"`
 }
 
diff --git a/api/types_test.go b/api/types_test.go
index 5053c1621..187012db2 100644
--- a/api/types_test.go
+++ b/api/types_test.go
@@ -298,6 +298,44 @@ func TestToolFunction_UnmarshalJSON(t *testing.T) {
 	}
 }
 
+func TestToolFunctionParameters_MarshalJSON(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    ToolFunctionParameters
+		expected string
+	}{
+		{
+			name: "simple object with string property",
+			input: ToolFunctionParameters{
+				Type:     "object",
+				Required: []string{"name"},
+				Properties: map[string]ToolProperty{
+					"name": {Type: PropertyType{"string"}},
+				},
+			},
+			expected: `{"type":"object","required":["name"],"properties":{"name":{"type":"string"}}}`,
+		},
+		{
+			name: "no required",
+			input: ToolFunctionParameters{
+				Type: "object",
+				Properties: map[string]ToolProperty{
+					"name": {Type: PropertyType{"string"}},
+				},
+			},
+			expected: `{"type":"object","properties":{"name":{"type":"string"}}}`,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			data, err := json.Marshal(test.input)
+			require.NoError(t, err)
+			assert.Equal(t, test.expected, string(data))
+		})
+	}
+}
+
 func TestToolCallFunction_IndexAlwaysMarshals(t *testing.T) {
 	fn := ToolCallFunction{
 		Name:      "echo",
diff --git a/middleware/openai_test.go b/middleware/openai_test.go
index a78ee8b91..e5cb245b0 100644
--- a/middleware/openai_test.go
+++ b/middleware/openai_test.go
@@ -484,13 +484,7 @@ func TestChatMiddleware(t *testing.T) {
 						Function: api.ToolFunction{
 							Name:        "get_weather",
 							Description: "Get the current weather",
-							Parameters: struct {
-								Type       string                      `json:"type"`
-								Defs       any                         `json:"$defs,omitempty"`
-								Items      any                         `json:"items,omitempty"`
-								Required   []string                    `json:"required"`
-								Properties map[string]api.ToolProperty `json:"properties"`
-							}{
+							Parameters: api.ToolFunctionParameters{
 								Type:     "object",
 								Required: []string{"location"},
 								Properties: map[string]api.ToolProperty{
diff --git a/server/routes_debug_test.go b/server/routes_debug_test.go
index bf822c68b..6f9104c39 100644
--- a/server/routes_debug_test.go
+++ b/server/routes_debug_test.go
@@ -363,7 +363,7 @@ func TestChatDebugRenderOnly(t *testing.T) {
 				DebugRenderOnly: true,
 			},
 			expectDebug:    true,
-			expectTemplate: "[{\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"description\":\"Get weather information\",\"parameters\":{\"type\":\"\",\"required\":null,\"properties\":null}}}]user: Get the weather\n",
+			expectTemplate: "[{\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"description\":\"Get weather information\",\"parameters\":{\"type\":\"\",\"properties\":null}}}]user: Get the weather\n",
 		},
 	}
 
diff --git a/server/routes_generate_test.go b/server/routes_generate_test.go
index ecd1d2d63..ed5922f2d 100644
--- a/server/routes_generate_test.go
+++ b/server/routes_generate_test.go
@@ -485,13 +485,7 @@ func TestGenerateChat(t *testing.T) {
 				Function: api.ToolFunction{
 					Name:        "get_weather",
 					Description: "Get the current weather",
-					Parameters: struct {
-						Type       string                      `json:"type"`
-						Defs       any                         `json:"$defs,omitempty"`
-						Items      any                         `json:"items,omitempty"`
-						Required   []string                    `json:"required"`
-						Properties map[string]api.ToolProperty `json:"properties"`
-					}{
+					Parameters: api.ToolFunctionParameters{
 						Type:     "object",
 						Required: []string{"location"},
 						Properties: map[string]api.ToolProperty{
@@ -585,13 +579,7 @@ func TestGenerateChat(t *testing.T) {
 				Function: api.ToolFunction{
 					Name:        "get_weather",
 					Description: "Get the current weather",
-					Parameters: struct {
-						Type       string                      `json:"type"`
-						Defs       any                         `json:"$defs,omitempty"`
-						Items      any                         `json:"items,omitempty"`
-						Required   []string                    `json:"required"`
-						Properties map[string]api.ToolProperty `json:"properties"`
-					}{
+					Parameters: api.ToolFunctionParameters{
 						Type:     "object",
 						Required: []string{"location"},
 						Properties: map[string]api.ToolProperty{
diff --git a/server/routes_harmony_streaming_test.go b/server/routes_harmony_streaming_test.go
index 8e58ad962..1fb41ff48 100644
--- a/server/routes_harmony_streaming_test.go
+++ b/server/routes_harmony_streaming_test.go
@@ -26,13 +26,7 @@ func getTestTools() []api.Tool {
 			Function: api.ToolFunction{
 				Name:        "get_weather",
 				Description: "Get the current weather in a given location",
-				Parameters: struct {
-					Type       string                      `json:"type"`
-					Defs       any                         `json:"$defs,omitempty"`
-					Items      any                         `json:"items,omitempty"`
-					Required   []string                    `json:"required"`
-					Properties map[string]api.ToolProperty `json:"properties"`
-				}{
+				Parameters: api.ToolFunctionParameters{
 					Type:     "object",
 					Required: []string{"location"},
 					Properties: map[string]api.ToolProperty{
@@ -49,13 +43,7 @@ func getTestTools() []api.Tool {
 			Function: api.ToolFunction{
 				Name:        "calculate",
 				Description: "Calculate a mathematical expression",
-				Parameters: struct {
-					Type       string                      `json:"type"`
-					Defs       any                         `json:"$defs,omitempty"`
-					Items      any                         `json:"items,omitempty"`
-					Required   []string                    `json:"required"`
-					Properties map[string]api.ToolProperty `json:"properties"`
-				}{
+				Parameters: api.ToolFunctionParameters{
 					Type:     "object",
 					Required: []string{"expression"},
 					Properties: map[string]api.ToolProperty{