diff --git a/functioncall/all_test.go b/functioncall/all_test.go
index 5e36f62..4f055eb 100644
--- a/functioncall/all_test.go
+++ b/functioncall/all_test.go
@@ -2,6 +2,7 @@ package functioncall
 
 import (
 	"encoding/json"
+	"reflect"
 	"testing"
 
 	. "github.com/otiai10/mint"
@@ -20,9 +21,9 @@ func TestFunctions_MarshalJSON(t *testing.T) {
 		return r
 	}
 	funcs := Funcs{
-		"repeat": Func{repeat, "Repeat given string N times", Params{
-			{"word", "string", "String to be repeated", true},
-			{"count", "number", "How many times to repeat", true},
+		"repeat": Func{Value: repeat, Description: "Repeat given string N times", Parameters: Params{
+			{Name: "word", Type: "string", Description: "String to be repeated", Required: true},
+			{Name: "count", Type: "number", Description: "How many times to repeat", Required: true},
 		}},
 	}
 	b, err := funcs.MarshalJSON()
@@ -47,9 +48,9 @@ func TestAs(t *testing.T) {
 		return r
 	}
 	funcs := Funcs{
-		"repeat": Func{repeat, "Repeat given string N times", Params{
-			{"word", "string", "String to be repeated", true},
-			{"count", "number", "How many times to repeat", true},
+		"repeat": Func{Value: repeat, Description: "Repeat given string N times", Parameters: Params{
+			{Name: "word", Type: "string", Description: "String to be repeated", Required: true},
+			{Name: "count", Type: "number", Description: "How many times to repeat", Required: true},
 		}},
 	}
 	a := As[[]map[string]any](funcs)
@@ -57,3 +58,101 @@ func TestAs(t *testing.T) {
 	Expect(t, a).Query("0.name").ToBe("repeat")
 	Expect(t, a).Query("0.parameters.type").ToBe("object")
 }
+
+func TestParams_MarshalJSON(t *testing.T) {
+	tests := []struct {
+		name    string
+		params  Params
+		want    []byte
+		wantErr bool
+	}{
+		{
+			name: "nested",
+			params: []Param{
+				{
+					Name:        "quality",
+					Type:        "object",
+					Description: "",
+					Required:    true,
+					Items: []Param{
+						{
+							Name:        "pros",
+							Type:        "array",
+							Description: "Write 3 points why this text is well written",
+							Required:    true,
+							Items: []Param{
+								{Type: "string"},
+							},
+						},
+					},
+				},
+			},
+			want:    []byte(`{"properties":{"quality":{"properties":{"pros":{"description":"Write 3 points why this text is well written","items":{"type":"string"},"type":"array"}},"required":["pros"],"type":"object"}},"required":["quality"],"type":"object"}`),
+			wantErr: false,
+		},
+		{
+			name: "nested_example",
+			params: []Param{
+				{
+					Name:     "ingredients",
+					Type:     "array",
+					Required: true,
+					Items: []Param{
+						{
+							Type: "object",
+							Items: []Param{
+								{
+									Name:     "name",
+									Type:     "string",
+									Required: true,
+								},
+								{
+									Name: "unit",
+									Type: "string",
+									// Enum: []any{"grams", "ml", "cups", "pieces", "teaspoons"},
+									Required: true,
+								},
+								{
+									Name:     "amount",
+									Type:     "number",
+									Required: true,
+								},
+							},
+						},
+					},
+				},
+				{
+					Name:     "instructions",
+					Type:     "array",
+					Required: true,
+					Items: []Param{
+						{
+							Type: "string",
+						},
+					},
+					Description: "Steps to prepare the recipe (no numbering)",
+				},
+				{
+					Name:        "time_to_cook",
+					Type:        "number",
+					Description: "Total time to prepare the recipe in minutes",
+					Required:    true,
+				},
+			},
+			want:    []byte(`{"properties":{"ingredients":{"items":{"properties":{"amount":{"type":"number"},"name":{"type":"string"},"unit":{"type":"string"}},"required":["name","unit","amount"],"type":"object"},"type":"array"},"instructions":{"description":"Steps to prepare the recipe (no numbering)","items":{"type":"string"},"type":"array"},"time_to_cook":{"type":"number","description":"Total time to prepare the recipe in minutes"}},"required":["ingredients","instructions","time_to_cook"],"type":"object"}`),
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := json.Marshal(tt.params)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("MarshalJSON() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("MarshalJSON() got = %s, want %s", got, tt.want)
+			}
+		})
+	}
+}
diff --git a/functioncall/functioncall.go b/functioncall/functioncall.go
index 0ccbe48..d804f4c 100644
--- a/functioncall/functioncall.go
+++ b/functioncall/functioncall.go
@@ -14,12 +14,15 @@ type Func struct {
 
 type Params []Param
 
+type NestedParams []Param
+
 type Param struct {
 	Name        string `json:"-"`
 	Type        string `json:"type,omitempty"`
 	Description string `json:"description,omitempty"`
 	Required    bool   `json:"-"`
 	// Enum        []any  `json:"enum,omitempty"`
+	Items NestedParams `json:",omitempty"`
 }
 
 func (funcs Funcs) MarshalJSON() ([]byte, error) {
@@ -37,6 +40,18 @@ func (funcs Funcs) MarshalJSON() ([]byte, error) {
 }
 
 func (params Params) MarshalJSON() ([]byte, error) {
+	return marshalObject(params)
+}
+
+func (params NestedParams) MarshalJSON() ([]byte, error) {
+	if len(params) == 1 {
+		return json.Marshal(params[0])
+	}
+
+	return marshalObject(params)
+}
+
+func marshalObject[T ~[]Param](params T) ([]byte, error) {
 	required := []string{}
 	props := map[string]Param{}
 	for _, p := range params {
@@ -45,6 +60,7 @@ func (params Params) MarshalJSON() ([]byte, error) {
 		}
 		props[p.Name] = p
 	}
+
 	schema := map[string]any{
 		"type":       "object",
 		"properties": props,
@@ -53,6 +69,25 @@ func (params Params) MarshalJSON() ([]byte, error) {
 	return json.Marshal(schema)
 }
 
+func (param Param) MarshalJSON() ([]byte, error) {
+	switch param.Type {
+	case "array":
+		schema := map[string]any{
+			"type":  "array",
+			"items": param.Items,
+		}
+		if param.Description != "" {
+			schema["description"] = param.Description
+		}
+		return json.Marshal(schema)
+	case "object":
+		return marshalObject(param.Items)
+	default:
+		type Alias Param
+		return json.Marshal(Alias(param))
+	}
+}
+
 func As[T any](funcs Funcs) (dest T) {
 	b, err := funcs.MarshalJSON()
 	if err != nil {