diff --git a/src/feature/auth/application/auth-query.ts b/src/feature/auth/application/auth-query.ts
index c5f1f1c..784a1c9 100644
--- a/src/feature/auth/application/auth-query.ts
+++ b/src/feature/auth/application/auth-query.ts
@@ -1,6 +1,7 @@
 import { useMutation } from '@tanstack/react-query';
 import { useGuardContext } from '@/feature/shared/context/use-gaurd-context';
 import { UsecaseContext } from '@/feature/shared/context/usecase-context';
+import { createErrorMessage } from '@/feature/shared/error/create-error-message';
 import { useRouteNavigation } from '@/routes/use-route-navigation';
 import type { UserRole } from '../domain/user-role';
 
@@ -26,12 +27,14 @@ export const useSignIn = ({
     onSuccess: (response) => {
       if (response.type === 'success') {
         toMain();
-      } else {
-        if (response.code === 'AUTH_002' || response.code === 'GEN_004') {
-          setResponseMessage('아이디 또는 비밀번호가 일치하지 않습니다.');
-          return;
-        }
+        return;
       }
+      setResponseMessage(
+        createErrorMessage(
+          response.code,
+          '로그인에 실패했습니다. 다시 시도해 주세요.'
+        )
+      );
     },
   });
 
@@ -67,13 +70,14 @@ export const useSignUp = ({
     onSuccess: (response) => {
       if (response.type === 'success') {
         toMain();
-      } else {
-        if (response.code === 'USER_003') {
-          setResponseMessage('이미 존재하는 이메일입니다.');
-          return;
-        }
-        setResponseMessage('회원가입에 실패했습니다. 다시 시도해주세요.');
+        return;
       }
+      setResponseMessage(
+        createErrorMessage(
+          response.code,
+          '회원가입에 실패했습니다. 다시 시도해 주세요.'
+        )
+      );
     },
   });
 
diff --git a/src/feature/shared/error/create-error-message.ts b/src/feature/shared/error/create-error-message.ts
new file mode 100644
index 0000000..2c88284
--- /dev/null
+++ b/src/feature/shared/error/create-error-message.ts
@@ -0,0 +1,43 @@
+const ERROR_MESSAGES: Record<string, string> = {
+  // Auth
+  AUTH_001: '인증 헤더가 없거나 형식이 올바르지 않습니다.',
+  AUTH_002: '이메일 또는 비밀번호가 일치하지 않습니다.',
+  AUTH_003: '리프레시 토큰이 유효하지 않습니다.',
+  AUTH_004: '액세스 토큰이 유효하지 않습니다.',
+  AUTH_005: '토큰 정보가 일치하지 않습니다.',
+  AUTH_006: 'OAuth 인증에 실패했습니다.',
+  AUTH_007: '이 작업을 수행할 권한이 없습니다.',
+  // User
+  USER_001: '이미 사용 중인 이메일입니다.',
+  USER_002: '이미 사용 중인 아이디입니다.',
+  USER_004: '사용자를 찾을 수 없습니다.',
+  USER_006: '이메일 인증 코드가 유효하지 않거나 만료되었습니다.',
+  USER_007: '이메일 인증에 실패했습니다.',
+  // General
+  GEN_002: '지원하지 않는 기능입니다.',
+  GEN_003: '잘못된 요청입니다.',
+  GEN_004: '필수 항목을 모두 입력해 주세요.',
+  GEN_005: '요청 형식이 올바르지 않습니다.',
+  // Store
+  STORE_001: '가게를 찾을 수 없습니다.',
+  // Event
+  EVENT_001: '이벤트를 찾을 수 없습니다.',
+  // Application
+  APPLICATION_001: '이 신청에 접근할 권한이 없습니다.',
+  APPLICATION_002: '신청 내역을 찾을 수 없습니다.',
+  APPLICATION_003: '이미 제출된 신청입니다.',
+  // Deposit
+  DEPOSIT_001: '예치금이 부족합니다.',
+  DEPOSIT_002: '예치금 정보를 찾을 수 없습니다.',
+  // S3
+  S3_001: '파일 업로드 URL 생성에 실패했습니다.',
+};
+
+const FALLBACK_MESSAGE = '오류가 발생했습니다. 다시 시도해 주세요.';
+
+export const createErrorMessage = (
+  code: string,
+  fallback = FALLBACK_MESSAGE
+): string => {
+  return ERROR_MESSAGES[code] ?? fallback;
+};
diff --git a/src/mocks/application/resolvers.ts b/src/mocks/application/resolvers.ts
index 2947606..5491c63 100644
--- a/src/mocks/application/resolvers.ts
+++ b/src/mocks/application/resolvers.ts
@@ -38,15 +38,30 @@ export const applicationResolver: ApplicationResolver = {
     const { eventId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const event = mockEvents.find((e) => e.id === eventId);
     if (!event) {
-      return HttpResponse.json({ message: 'Event not found' }, { status: 404 });
+      return HttpResponse.json(
+        { code: 'EVENT_001', message: 'Event not found' },
+        { status: 404 }
+      );
     }
 
     const url = new URL(request.url);
@@ -75,28 +90,49 @@ export const applicationResolver: ApplicationResolver = {
     const { eventId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'REVIEWER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const event = mockEvents.find((e) => e.id === eventId);
     if (!event) {
-      return HttpResponse.json({ message: 'Event not found' }, { status: 404 });
+      return HttpResponse.json(
+        { code: 'EVENT_001', message: 'Event not found' },
+        { status: 404 }
+      );
     }
 
     // 이미 마감된 이벤트
     if (!event.isActive) {
       return HttpResponse.json(
-        { message: 'Event already closed' },
+        { code: 'GEN_003', message: 'Event is already closed' },
         { status: 400 }
       );
     }
 
     // 이미 신청한 이벤트 → ALREADY_APPLIED_EVENT_ID 사용
     if (eventId === ALREADY_APPLIED_EVENT_ID) {
-      return HttpResponse.json({ message: 'Already applied' }, { status: 409 });
+      return HttpResponse.json(
+        {
+          code: 'APPLICATION_003',
+          message: 'You have already applied for this event',
+        },
+        { status: 409 }
+      );
     }
 
     return HttpResponse.json(null, { status: 200 });
@@ -106,10 +142,22 @@ export const applicationResolver: ApplicationResolver = {
   getMyApplications: ({ request }) => {
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'REVIEWER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     return HttpResponse.json({
@@ -126,20 +174,32 @@ export const applicationResolver: ApplicationResolver = {
     const { applicationId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
 
     const app = mockApplications.find((a) => a.id === applicationId);
     if (!app) {
       return HttpResponse.json(
-        { message: 'Application not found' },
+        { code: 'APPLICATION_002', message: 'Application not found' },
         { status: 404 }
       );
     }
 
     // 해당 신청의 신청자가 아닌 경우 시뮬레이션: OWNER가 접근하면 403
     if (role === 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'APPLICATION_001',
+          message: 'You are not allowed to access this application',
+        },
+        { status: 403 }
+      );
     }
 
     return HttpResponse.json(null, { status: 200 });
@@ -150,13 +210,19 @@ export const applicationResolver: ApplicationResolver = {
     const { applicationId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
 
     const app = mockApplications.find((a) => a.id === applicationId);
     if (!app) {
       return HttpResponse.json(
-        { message: 'Application not found' },
+        { code: 'APPLICATION_002', message: 'Application not found' },
         { status: 404 }
       );
     }
@@ -164,14 +230,23 @@ export const applicationResolver: ApplicationResolver = {
     // 이미 인증을 제출한 신청 → ALREADY_SUBMITTED_APP_ID 사용
     if (applicationId === ALREADY_SUBMITTED_APP_ID) {
       return HttpResponse.json(
-        { message: 'Review already submitted' },
+        {
+          code: 'APPLICATION_003',
+          message: 'Review has already been submitted for this application',
+        },
         { status: 409 }
       );
     }
 
     // 해당 신청의 신청자가 아닌 경우: OWNER가 접근하면 403
     if (role === 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'APPLICATION_001',
+          message: 'You are not allowed to access this application',
+        },
+        { status: 403 }
+      );
     }
 
     return HttpResponse.json(null, { status: 200 });
@@ -182,16 +257,28 @@ export const applicationResolver: ApplicationResolver = {
     const { applicationId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const app = mockApplications.find((a) => a.id === applicationId);
     if (!app) {
       return HttpResponse.json(
-        { message: 'Application not found' },
+        { code: 'APPLICATION_002', message: 'Application not found' },
         { status: 404 }
       );
     }
diff --git a/src/mocks/auth/resolvers.ts b/src/mocks/auth/resolvers.ts
index a1bf214..9df21da 100644
--- a/src/mocks/auth/resolvers.ts
+++ b/src/mocks/auth/resolvers.ts
@@ -13,7 +13,7 @@ export const authResolver: AuthResolver = {
 
     if (!body.role || !body.username || !body.email || !body.password) {
       return HttpResponse.json(
-        { message: 'Required field missing' },
+        { code: 'GEN_004', message: 'Required fields are missing or invalid' },
         { status: 400 }
       );
     }
@@ -21,7 +21,7 @@ export const authResolver: AuthResolver = {
     // 중복 이메일
     if (body.email === 'duplicate@example.com') {
       return HttpResponse.json(
-        { message: 'Email already exists' },
+        { code: 'USER_001', message: 'This email is already registered' },
         { status: 409 }
       );
     }
@@ -29,7 +29,10 @@ export const authResolver: AuthResolver = {
     // 리뷰어: 이메일 인증 코드 만료 시뮬레이션 (email에 +fail 포함)
     if (body.role === 'REVIEWER' && body.email.includes('+fail')) {
       return HttpResponse.json(
-        { message: 'Email verification code expired or invalid' },
+        {
+          code: 'USER_006',
+          message: 'Email verification code is invalid or expired',
+        },
         { status: 400 }
       );
     }
@@ -37,7 +40,7 @@ export const authResolver: AuthResolver = {
     // 사장님: 사전 설정된 비밀번호 불일치
     if (body.role === 'OWNER' && body.password === 'wrong-owner-secret') {
       return HttpResponse.json(
-        { message: 'Owner password mismatch' },
+        { code: 'AUTH_002', message: 'Invalid credentials' },
         { status: 401 }
       );
     }
@@ -51,7 +54,7 @@ export const authResolver: AuthResolver = {
 
     if (!body.role || !body.mail || !body.password) {
       return HttpResponse.json(
-        { message: 'Required field missing' },
+        { code: 'GEN_004', message: 'Required fields are missing or invalid' },
         { status: 400 }
       );
     }
@@ -62,7 +65,7 @@ export const authResolver: AuthResolver = {
       body.password === 'wrongpassword'
     ) {
       return HttpResponse.json(
-        { message: 'Invalid credentials' },
+        { code: 'AUTH_002', message: 'Invalid credentials' },
         { status: 401 }
       );
     }
diff --git a/src/mocks/deposit/resolvers.ts b/src/mocks/deposit/resolvers.ts
index 34ca9aa..9ed975d 100644
--- a/src/mocks/deposit/resolvers.ts
+++ b/src/mocks/deposit/resolvers.ts
@@ -13,16 +13,28 @@ export const depositResolver: DepositResolver = {
   getDeposit: ({ request }) => {
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     // 예치금 정보가 없는 사장님 시뮬레이션 (NO_DEPOSIT_OWNER_TOKEN 사용)
     if (request.headers.get('Authorization') === NO_DEPOSIT_OWNER_TOKEN) {
       return HttpResponse.json(
-        { message: 'Deposit not found' },
+        { code: 'DEPOSIT_002', message: 'Deposit record not found' },
         { status: 404 }
       );
     }
@@ -33,15 +45,30 @@ export const depositResolver: DepositResolver = {
   chargeDeposit: async ({ request }) => {
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const body = (await request.json()) as DepositRequest;
     if (body.amount == null || body.amount <= 0) {
-      return HttpResponse.json({ message: 'Invalid amount' }, { status: 400 });
+      return HttpResponse.json(
+        { code: 'GEN_003', message: 'Amount must be a positive number' },
+        { status: 400 }
+      );
     }
 
     return HttpResponse.json(
diff --git a/src/mocks/event/resolvers.ts b/src/mocks/event/resolvers.ts
index ae068e6..0d049c4 100644
--- a/src/mocks/event/resolvers.ts
+++ b/src/mocks/event/resolvers.ts
@@ -19,16 +19,28 @@ export const eventResolver: EventResolver = {
   createEvent: async ({ request }) => {
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const body = (await request.json()) as EventCreateRequest;
     if (!body.title || !body.condition || body.reward == null) {
       return HttpResponse.json(
-        { message: 'Required field missing' },
+        { code: 'GEN_004', message: 'Required fields are missing or invalid' },
         { status: 400 }
       );
     }
@@ -36,7 +48,7 @@ export const eventResolver: EventResolver = {
     // reward >= INSUFFICIENT_DEPOSIT_REWARD → 예치금 부족
     if (body.reward >= INSUFFICIENT_DEPOSIT_REWARD) {
       return HttpResponse.json(
-        { message: 'Insufficient deposit' },
+        { code: 'DEPOSIT_001', message: 'Deposit balance is insufficient' },
         { status: 400 }
       );
     }
@@ -56,10 +68,22 @@ export const eventResolver: EventResolver = {
   getOwnerEvents: ({ request }) => {
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     return HttpResponse.json({ events: mockEvents });
@@ -69,15 +93,30 @@ export const eventResolver: EventResolver = {
     const { eventId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const event = mockEvents.find((e) => e.id === eventId);
     if (!event) {
-      return HttpResponse.json({ message: 'Event not found' }, { status: 404 });
+      return HttpResponse.json(
+        { code: 'EVENT_001', message: 'Event not found' },
+        { status: 404 }
+      );
     }
 
     const body = (await request.json()) as EventPatchRequest;
@@ -85,7 +124,7 @@ export const eventResolver: EventResolver = {
     // isActive: false로 이미 마감된 이벤트를 다시 마감하려 할 때
     if (body.isActive === false && !event.isActive) {
       return HttpResponse.json(
-        { message: 'Event already closed' },
+        { code: 'GEN_003', message: 'Event is already closed' },
         { status: 400 }
       );
     }
@@ -97,15 +136,30 @@ export const eventResolver: EventResolver = {
     const { eventId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const event = mockEvents.find((e) => e.id === eventId);
     if (!event) {
-      return HttpResponse.json({ message: 'Event not found' }, { status: 404 });
+      return HttpResponse.json(
+        { code: 'EVENT_001', message: 'Event not found' },
+        { status: 404 }
+      );
     }
 
     return HttpResponse.json(null, { status: 200 });
diff --git a/src/mocks/s3/resolvers.ts b/src/mocks/s3/resolvers.ts
index 6eae789..b28dcd9 100644
--- a/src/mocks/s3/resolvers.ts
+++ b/src/mocks/s3/resolvers.ts
@@ -12,13 +12,19 @@ export const s3Resolver: S3Resolver = {
   getPresignedUrl: async ({ request }) => {
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
 
     const body = (await request.json()) as S3UploadRequest;
     if (!body.fileName || !body.fileType) {
       return HttpResponse.json(
-        { message: 'Required field missing' },
+        { code: 'GEN_004', message: 'Required fields are missing or invalid' },
         { status: 400 }
       );
     }
diff --git a/src/mocks/store/resolvers.ts b/src/mocks/store/resolvers.ts
index 9f9b367..1b4011d 100644
--- a/src/mocks/store/resolvers.ts
+++ b/src/mocks/store/resolvers.ts
@@ -29,16 +29,28 @@ export const storeResolver: StoreResolver = {
   createStore: async ({ request }) => {
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const body = (await request.json()) as StoreCreateRequest;
     if (!body.name || !body.address || !body.category) {
       return HttpResponse.json(
-        { message: 'Required field missing' },
+        { code: 'GEN_004', message: 'Required fields are missing or invalid' },
         { status: 400 }
       );
     }
@@ -80,15 +92,30 @@ export const storeResolver: StoreResolver = {
     const { storeId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const store = mockStores.find((s) => s.id === storeId);
     if (!store) {
-      return HttpResponse.json({ message: 'Store not found' }, { status: 404 });
+      return HttpResponse.json(
+        { code: 'STORE_001', message: 'Store not found' },
+        { status: 404 }
+      );
     }
 
     const body = (await request.json()) as StorePatchRequest;
@@ -99,15 +126,30 @@ export const storeResolver: StoreResolver = {
     const { storeId } = params;
     const role = getRole(request);
     if (!role) {
-      return HttpResponse.json({ message: 'Unauthorized' }, { status: 401 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_001',
+          message: 'Authorization header is missing or malformed',
+        },
+        { status: 401 }
+      );
     }
     if (role !== 'OWNER') {
-      return HttpResponse.json({ message: 'Forbidden' }, { status: 403 });
+      return HttpResponse.json(
+        {
+          code: 'AUTH_007',
+          message: 'You do not have permission to perform this action',
+        },
+        { status: 401 }
+      );
     }
 
     const store = mockStores.find((s) => s.id === storeId);
     if (!store) {
-      return HttpResponse.json({ message: 'Store not found' }, { status: 404 });
+      return HttpResponse.json(
+        { code: 'STORE_001', message: 'Store not found' },
+        { status: 404 }
+      );
     }
 
     return HttpResponse.json(null, { status: 200 });
@@ -117,7 +159,10 @@ export const storeResolver: StoreResolver = {
     const { storeId } = params;
     const store = mockStores.find((s) => s.id === storeId);
     if (!store) {
-      return HttpResponse.json({ message: 'Store not found' }, { status: 404 });
+      return HttpResponse.json(
+        { code: 'STORE_001', message: 'Store not found' },
+        { status: 404 }
+      );
     }
 
     return HttpResponse.json({ events: store.events });