diff --git a/minmax.go b/minmax.go
index fa3b23a..c2e7a31 100644
--- a/minmax.go
+++ b/minmax.go
@@ -59,7 +59,7 @@ func (r *ThresholdRule) Exclusive() *ThresholdRule {
 }
 
 // Validate checks if the given value is valid or not.
-func (r *ThresholdRule) Validate(value interface{}) error {
+func (r *ThresholdRule) Validate(value interface{}) ExternalError {
 	value, isNil := Indirect(value)
 	if isNil || IsEmpty(value) {
 		return nil
@@ -70,7 +70,7 @@ func (r *ThresholdRule) Validate(value interface{}) error {
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 		v, err := ToInt(value)
 		if err != nil {
-			return err
+			return NewExternalError(err, 1000)
 		}
 		if r.compareInt(rv.Int(), v) {
 			return nil
@@ -79,7 +79,7 @@ func (r *ThresholdRule) Validate(value interface{}) error {
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
 		v, err := ToUint(value)
 		if err != nil {
-			return err
+			return NewExternalError(err, 1000)
 		}
 		if r.compareUint(rv.Uint(), v) {
 			return nil
@@ -88,7 +88,7 @@ func (r *ThresholdRule) Validate(value interface{}) error {
 	case reflect.Float32, reflect.Float64:
 		v, err := ToFloat(value)
 		if err != nil {
-			return err
+			return NewExternalError(err, 1000)
 		}
 		if r.compareFloat(rv.Float(), v) {
 			return nil
@@ -97,21 +97,21 @@ func (r *ThresholdRule) Validate(value interface{}) error {
 	case reflect.Struct:
 		t, ok := r.threshold.(time.Time)
 		if !ok {
-			return fmt.Errorf("type not supported: %v", rv.Type())
+			return NewExternalError(fmt.Errorf("type not supported: %v", rv.Type()), 1000)
 		}
 		v, ok := value.(time.Time)
 		if !ok {
-			return fmt.Errorf("cannot convert %v to time.Time", reflect.TypeOf(value))
+			return NewExternalError(fmt.Errorf("cannot convert %v to time.Time", reflect.TypeOf(value)), 1000)
 		}
 		if v.IsZero() || r.compareTime(t, v) {
 			return nil
 		}
 
 	default:
-		return fmt.Errorf("type not supported: %v", rv.Type())
+		return NewExternalError(fmt.Errorf("type not supported: %v", rv.Type()), 1000)
 	}
 
-	return errors.New(r.message)
+	return NewExternalError(errors.New(r.message), 1000)
 }
 
 // Error sets the error message for the rule.
diff --git a/minmax_test.go b/minmax_test.go
index f746f4c..ad54423 100644
--- a/minmax_test.go
+++ b/minmax_test.go
@@ -23,33 +23,33 @@ func TestMin(t *testing.T) {
 		// int cases
 		{"t1.1", 1, false, 1, ""},
 		{"t1.2", 1, false, 2, ""},
-		{"t1.3", 1, false, -1, "must be no less than 1"},
+		{"t1.3", 1, false, -1, "must be no less than 1, ErrCode: 1000"},
 		{"t1.4", 1, false, 0, ""},
-		{"t1.5", 1, true, 1, "must be greater than 1"},
-		{"t1.6", 1, false, "1", "cannot convert string to int64"},
-		{"t1.7", "1", false, 1, "type not supported: string"},
+		{"t1.5", 1, true, 1, "must be greater than 1, ErrCode: 1000"},
+		{"t1.6", 1, false, "1", "cannot convert string to int64, ErrCode: 1000"},
+		{"t1.7", "1", false, 1, "type not supported: string, ErrCode: 1000"},
 		// uint cases
 		{"t2.1", uint(2), false, uint(2), ""},
 		{"t2.2", uint(2), false, uint(3), ""},
-		{"t2.3", uint(2), false, uint(1), "must be no less than 2"},
+		{"t2.3", uint(2), false, uint(1), "must be no less than 2, ErrCode: 1000"},
 		{"t2.4", uint(2), false, uint(0), ""},
-		{"t2.5", uint(2), true, uint(2), "must be greater than 2"},
-		{"t2.6", uint(2), false, "1", "cannot convert string to uint64"},
+		{"t2.5", uint(2), true, uint(2), "must be greater than 2, ErrCode: 1000"},
+		{"t2.6", uint(2), false, "1", "cannot convert string to uint64, ErrCode: 1000"},
 		// float cases
 		{"t3.1", float64(2), false, float64(2), ""},
 		{"t3.2", float64(2), false, float64(3), ""},
-		{"t3.3", float64(2), false, float64(1), "must be no less than 2"},
+		{"t3.3", float64(2), false, float64(1), "must be no less than 2, ErrCode: 1000"},
 		{"t3.4", float64(2), false, float64(0), ""},
-		{"t3.5", float64(2), true, float64(2), "must be greater than 2"},
-		{"t3.6", float64(2), false, "1", "cannot convert string to float64"},
+		{"t3.5", float64(2), true, float64(2), "must be greater than 2, ErrCode: 1000"},
+		{"t3.6", float64(2), false, "1", "cannot convert string to float64, ErrCode: 1000"},
 		// Time cases
 		{"t4.1", date20000601, false, date20000601, ""},
 		{"t4.2", date20000601, false, date20001201, ""},
-		{"t4.3", date20000601, false, date20000101, "must be no less than 2000-06-01 00:00:00 +0000 UTC"},
+		{"t4.3", date20000601, false, date20000101, "must be no less than 2000-06-01 00:00:00 +0000 UTC, ErrCode: 1000"},
 		{"t4.4", date20000601, false, date0, ""},
-		{"t4.5", date20000601, true, date20000601, "must be greater than 2000-06-01 00:00:00 +0000 UTC"},
-		{"t4.6", date20000601, true, 1, "cannot convert int to time.Time"},
-		{"t4.7", struct{}{}, false, 1, "type not supported: struct {}"},
+		{"t4.5", date20000601, true, date20000601, "must be greater than 2000-06-01 00:00:00 +0000 UTC, ErrCode: 1000"},
+		{"t4.6", date20000601, true, 1, "cannot convert int to time.Time, ErrCode: 1000"},
+		{"t4.7", struct{}{}, false, 1, "type not supported: struct {}, ErrCode: 1000"},
 		{"t4.8", date0, false, date20000601, ""},
 	}