diff --git a/example/validation/validation.go b/example/validation/validation.go
index 480275c..00122fa 100644
--- a/example/validation/validation.go
+++ b/example/validation/validation.go
@@ -12,6 +12,7 @@ type user struct {
 	Name    string `validate:"required" mod:"trim"`
 	Age     int    `validate:"gt=10"`
 	Magic   string `mod:"magic"`
+	Skill   string `mod:"skill=expert"`
 	Country string `validate:"contain=konoha" mod:"lcase"`
 }
 
@@ -20,9 +21,12 @@ func main() {
 	v := validation.New(true)
 
 	// Register custom modifier.
-	v.RegisterModifier("magic", func(in string) string {
+	v.RegisterModifier("magic", func(in string, _ ...string) string {
 		return in + " magic"
 	})
+	v.RegisterModifier("skill", func(in string, param ...string) string {
+		return fmt.Sprintf("%s (%s)", in, param[0])
+	})
 
 	// Register custom validator.
 	v.RegisterValidator("contain", func(value interface{}, param ...string) bool {
@@ -42,6 +46,7 @@ func main() {
 		Name:    "  Naruto ",
 		Age:     15,
 		Magic:   "ninja",
+		Skill:   "jump",
 		Country: "Konohagakure",
 	}
 
diff --git a/validation/playground/playground.go b/validation/playground/playground.go
index ddee086..aa020d7 100644
--- a/validation/playground/playground.go
+++ b/validation/playground/playground.go
@@ -43,7 +43,7 @@ func New(autoMod bool) *Validator {
 }
 
 // RegisterModifier to register custom modifier.
-func (v *Validator) RegisterModifier(name string, fn func(string) string) error {
+func (v *Validator) RegisterModifier(name string, fn func(string, ...string) string) error {
 	if name == "" {
 		return ErrRequiredName
 	}
@@ -55,7 +55,7 @@ func (v *Validator) RegisterModifier(name string, fn func(string) string) error
 	v.mod.Register(name, func(ctx context.Context, fl mold.FieldLevel) error {
 		switch fl.Field().Kind() {
 		case reflect.String:
-			fl.Field().SetString(fn(fl.Field().String()))
+			fl.Field().SetString(fn(fl.Field().String(), fl.Param()))
 		}
 		return nil
 	})
diff --git a/validation/validation.go b/validation/validation.go
index 4d33dcf..4eeb352 100644
--- a/validation/validation.go
+++ b/validation/validation.go
@@ -7,7 +7,7 @@ import "github.com/rl404/fairy/validation/playground"
 // See usage example in example folder.
 type Validator interface {
 	// Register custom modifier.
-	RegisterModifier(name string, fn func(in string) (out string)) error
+	RegisterModifier(name string, fn func(in string, param ...string) (out string)) error
 	// Modify struct field value according to modifier tag.
 	// Param `data` should be a pointer.
 	Modify(data interface{}) error