diff --git a/internal/sms-gateway/handlers/handler.go b/internal/sms-gateway/handlers/handler.go
index ef6b2f1..bec4914 100644
--- a/internal/sms-gateway/handlers/handler.go
+++ b/internal/sms-gateway/handlers/handler.go
@@ -8,6 +8,10 @@ import (
 	"go.uber.org/zap"
 )
 
+type Validatable interface {
+	Validate() error
+}
+
 type Handler struct {
 	Logger    *zap.Logger
 	Validator *validator.Validate
@@ -18,11 +22,7 @@ func (h *Handler) BodyParserValidator(c *fiber.Ctx, out any) error {
 		return fmt.Errorf("can't parse body: %w", err)
 	}
 
-	if h.Validator == nil {
-		return nil
-	}
-
-	return h.Validator.Struct(out)
+	return h.validateStruct(out)
 }
 
 func (h *Handler) QueryParserValidator(c *fiber.Ctx, out any) error {
@@ -30,11 +30,7 @@ func (h *Handler) QueryParserValidator(c *fiber.Ctx, out any) error {
 		return fmt.Errorf("can't parse query: %w", err)
 	}
 
-	if h.Validator == nil {
-		return nil
-	}
-
-	return h.Validator.Struct(out)
+	return h.validateStruct(out)
 }
 
 func (h *Handler) ParamsParserValidator(c *fiber.Ctx, out any) error {
@@ -42,9 +38,21 @@ func (h *Handler) ParamsParserValidator(c *fiber.Ctx, out any) error {
 		return fmt.Errorf("can't parse params: %w", err)
 	}
 
-	if h.Validator == nil {
-		return nil
+	return h.validateStruct(out)
+}
+
+func (h *Handler) validateStruct(out any) error {
+	if h.Validator != nil {
+		if err := h.Validator.Struct(out); err != nil {
+			return fiber.NewError(fiber.StatusBadRequest, err.Error())
+		}
 	}
 
-	return h.Validator.Struct(out)
+	if req, ok := out.(Validatable); ok {
+		if err := req.Validate(); err != nil {
+			return fiber.NewError(fiber.StatusBadRequest, err.Error())
+		}
+	}
+
+	return nil
 }
diff --git a/internal/sms-gateway/handlers/handler_test.go b/internal/sms-gateway/handlers/handler_test.go
new file mode 100644
index 0000000..4791ff9
--- /dev/null
+++ b/internal/sms-gateway/handlers/handler_test.go
@@ -0,0 +1,205 @@
+package handlers
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-playground/validator/v10"
+	"github.com/gofiber/fiber/v2"
+	"go.uber.org/zap"
+	"go.uber.org/zap/zaptest"
+)
+
+type TestRequestBody struct {
+	Name string `json:"name" validate:"required"`
+	Age  int    `json:"age" validate:"required"`
+}
+
+type TestRequestBodyNoValidate struct {
+	Name string `json:"name" validate:"required"`
+	Age  int    `json:"age" validate:"required"`
+}
+
+func (t *TestRequestBody) Validate() error {
+	if t.Age < 18 {
+		return fmt.Errorf("must be at least 18 years old")
+	}
+	return nil
+}
+
+type TestQueryParams struct {
+	Page int `query:"page" validate:"required"`
+}
+
+type TestURLParams struct {
+	ID string `params:"id" validate:"required,uuid"`
+}
+
+func TestHandler_BodyParserValidator(t *testing.T) {
+	logger := zaptest.NewLogger(t)
+	validate := validator.New()
+
+	handler := &Handler{
+		Logger:    logger,
+		Validator: validate,
+	}
+
+	app := fiber.New()
+	app.Post("/test", func(c *fiber.Ctx) error {
+		var body TestRequestBody
+		return handler.BodyParserValidator(c, &body)
+	})
+	app.Post("/test2", func(c *fiber.Ctx) error {
+		var body TestRequestBodyNoValidate
+		return handler.BodyParserValidator(c, &body)
+	})
+
+	tests := []struct {
+		description    string
+		path           string
+		payload        any
+		expectedStatus int
+	}{
+		{
+			description:    "Valid request body",
+			path:           "/test",
+			payload:        &TestRequestBody{Name: "John Doe", Age: 25},
+			expectedStatus: fiber.StatusOK,
+		},
+		{
+			description:    "Invalid request body - missing name",
+			path:           "/test",
+			payload:        &TestRequestBody{Age: 25},
+			expectedStatus: fiber.StatusBadRequest,
+		},
+		{
+			description:    "Invalid request body - age too low",
+			path:           "/test",
+			payload:        &TestRequestBody{Name: "John Doe", Age: 17},
+			expectedStatus: fiber.StatusBadRequest,
+		},
+		{
+			description:    "Valid request body - no validation",
+			path:           "/test2",
+			payload:        &TestRequestBodyNoValidate{Name: "John Doe", Age: 17},
+			expectedStatus: fiber.StatusOK,
+		},
+		{
+			description:    "No request body",
+			path:           "/test",
+			payload:        nil,
+			expectedStatus: fiber.StatusUnprocessableEntity,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.description, func(t *testing.T) {
+			var req *http.Request
+			if test.payload != nil {
+				bodyBytes, _ := json.Marshal(test.payload)
+				req = httptest.NewRequest("POST", test.path, bytes.NewReader(bodyBytes))
+				req.Header.Set("Content-Type", "application/json")
+			} else {
+				req = httptest.NewRequest("POST", test.path, nil)
+			}
+
+			resp, _ := app.Test(req)
+			if test.expectedStatus != resp.StatusCode {
+				t.Errorf("Expected status code %d, got %d", test.expectedStatus, resp.StatusCode)
+			}
+		})
+	}
+}
+
+func TestHandler_QueryParserValidator(t *testing.T) {
+	type fields struct {
+		Logger    *zap.Logger
+		Validator *validator.Validate
+	}
+	type args struct {
+		c   *fiber.Ctx
+		out any
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr bool
+	}{
+		// TODO: Add test cases.
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			h := &Handler{
+				Logger:    tt.fields.Logger,
+				Validator: tt.fields.Validator,
+			}
+			if err := h.QueryParserValidator(tt.args.c, tt.args.out); (err != nil) != tt.wantErr {
+				t.Errorf("Handler.QueryParserValidator() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestHandler_ParamsParserValidator(t *testing.T) {
+	type fields struct {
+		Logger    *zap.Logger
+		Validator *validator.Validate
+	}
+	type args struct {
+		c   *fiber.Ctx
+		out any
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr bool
+	}{
+		// TODO: Add test cases.
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			h := &Handler{
+				Logger:    tt.fields.Logger,
+				Validator: tt.fields.Validator,
+			}
+			if err := h.ParamsParserValidator(tt.args.c, tt.args.out); (err != nil) != tt.wantErr {
+				t.Errorf("Handler.ParamsParserValidator() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestHandler_validateStruct(t *testing.T) {
+	type fields struct {
+		Logger    *zap.Logger
+		Validator *validator.Validate
+	}
+	type args struct {
+		out any
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr bool
+	}{
+		// TODO: Add test cases.
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			h := &Handler{
+				Logger:    tt.fields.Logger,
+				Validator: tt.fields.Validator,
+			}
+			if err := h.validateStruct(tt.args.out); (err != nil) != tt.wantErr {
+				t.Errorf("Handler.validateStruct() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}