diff --git a/api/types.go b/api/types.go
index a3abc5568c..85bdd31671 100644
--- a/api/types.go
+++ b/api/types.go
@@ -286,16 +286,23 @@ func mapToTypeScriptType(jsonType string) string {
 	}
 }
 
+type ToolFunctionParameters struct {
+	Type       string                  `json:"type"`
+	Defs       any                     `json:"$defs,omitempty"`
+	Items      any                     `json:"items,omitempty"`
+	Required   []string                `json:"required"`
+	Properties map[string]ToolProperty `json:"properties"`
+}
+
+func (t *ToolFunctionParameters) String() string {
+	bts, _ := json.Marshal(t)
+	return string(bts)
+}
+
 type ToolFunction struct {
-	Name        string `json:"name"`
-	Description string `json:"description"`
-	Parameters  struct {
-		Type       string                  `json:"type"`
-		Defs       any                     `json:"$defs,omitempty"`
-		Items      any                     `json:"items,omitempty"`
-		Required   []string                `json:"required"`
-		Properties map[string]ToolProperty `json:"properties"`
-	} `json:"parameters"`
+	Name        string                 `json:"name"`
+	Description string                 `json:"description"`
+	Parameters  ToolFunctionParameters `json:"parameters"`
 }
 
 func (t *ToolFunction) String() string {
diff --git a/api/types_test.go b/api/types_test.go
index 8418538081..fadaa646d6 100644
--- a/api/types_test.go
+++ b/api/types_test.go
@@ -436,3 +436,50 @@ func TestThinking_UnmarshalJSON(t *testing.T) {
 		})
 	}
 }
+
+func TestToolFunctionParameters_String(t *testing.T) {
+	tests := []struct {
+		name     string
+		params   ToolFunctionParameters
+		expected string
+	}{
+		{
+			name: "simple object with string property",
+			params: ToolFunctionParameters{
+				Type:     "object",
+				Required: []string{"name"},
+				Properties: map[string]ToolProperty{
+					"name": {
+						Type:        PropertyType{"string"},
+						Description: "The name of the person",
+					},
+				},
+			},
+			expected: `{"type":"object","required":["name"],"properties":{"name":{"type":"string","description":"The name of the person"}}}`,
+		},
+		{
+			name: "marshal failure returns empty string",
+			params: ToolFunctionParameters{
+				Type: "object",
+				Defs: func() any {
+					// Create a cycle that will cause json.Marshal to fail
+					type selfRef struct {
+						Self *selfRef
+					}
+					s := &selfRef{}
+					s.Self = s
+					return s
+				}(),
+				Properties: map[string]ToolProperty{},
+			},
+			expected: "",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			result := test.params.String()
+			assert.Equal(t, test.expected, result)
+		})
+	}
+}
diff --git a/tools/tools_test.go b/tools/tools_test.go
index 36b552c964..2a449a0eac 100644
--- a/tools/tools_test.go
+++ b/tools/tools_test.go
@@ -41,13 +41,7 @@ func TestParser(t *testing.T) {
 			Function: api.ToolFunction{
 				Name:        "get_temperature",
 				Description: "Retrieve the temperature for a given location",
-				Parameters: struct {
-					Type       string                      `json:"type"`
-					Defs       any                         `json:"$defs,omitempty"`
-					Items      any                         `json:"items,omitempty"`
-					Required   []string                    `json:"required"`
-					Properties map[string]api.ToolProperty `json:"properties"`
-				}{
+				Parameters: api.ToolFunctionParameters{
 					Type:     "object",
 					Required: []string{"city"},
 					Properties: map[string]api.ToolProperty{
@@ -69,13 +63,7 @@ func TestParser(t *testing.T) {
 			Function: api.ToolFunction{
 				Name:        "get_conditions",
 				Description: "Retrieve the current weather conditions for a given location",
-				Parameters: struct {
-					Type       string                      `json:"type"`
-					Defs       any                         `json:"$defs,omitempty"`
-					Items      any                         `json:"items,omitempty"`
-					Required   []string                    `json:"required"`
-					Properties map[string]api.ToolProperty `json:"properties"`
-				}{
+				Parameters: api.ToolFunctionParameters{
 					Type: "object",
 					Properties: map[string]api.ToolProperty{
 						"location": {
@@ -105,13 +93,7 @@ func TestParser(t *testing.T) {
 			Function: api.ToolFunction{
 				Name:        "get_address",
 				Description: "Get the address of a given location",
-				Parameters: struct {
-					Type       string                      `json:"type"`
-					Defs       any                         `json:"$defs,omitempty"`
-					Items      any                         `json:"items,omitempty"`
-					Required   []string                    `json:"required"`
-					Properties map[string]api.ToolProperty `json:"properties"`
-				}{
+				Parameters: api.ToolFunctionParameters{
 					Type: "object",
 					Properties: map[string]api.ToolProperty{
 						"location": {
@@ -127,13 +109,7 @@ func TestParser(t *testing.T) {
 			Function: api.ToolFunction{
 				Name:        "add",
 				Description: "Add two numbers",
-				Parameters: struct {
-					Type       string                      `json:"type"`
-					Defs       any                         `json:"$defs,omitempty"`
-					Items      any                         `json:"items,omitempty"`
-					Required   []string                    `json:"required"`
-					Properties map[string]api.ToolProperty `json:"properties"`
-				}{
+				Parameters: api.ToolFunctionParameters{
 					Type: "object",
 					Properties: map[string]api.ToolProperty{
 						"a": {