diff --git a/apps/client/package.json b/apps/client/package.json
index ba5b8693..6055c74d 100644
--- a/apps/client/package.json
+++ b/apps/client/package.json
@@ -10,6 +10,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@pinback/contracts": "workspace:*",
     "@tanstack/react-query": "^5.85.3",
     "axios": "^1.11.0",
     "class-variance-authority": "^0.7.1",
diff --git a/apps/client/src/layout/Layout.tsx b/apps/client/src/layout/Layout.tsx
index bab24695..cb509250 100644
--- a/apps/client/src/layout/Layout.tsx
+++ b/apps/client/src/layout/Layout.tsx
@@ -2,6 +2,7 @@ import { ROUTES_CONFIG } from '@routes/routesConfig';
 import { useGetHasJob } from '@shared/apis/queries';
 import JobSelectionFunnel from '@shared/components/jobSelectionFunnel/JobSelectionFunnel';
 import { Sidebar } from '@shared/components/sidebar/Sidebar';
+import { authStorage } from '@shared/utils/authStorage';
 import { useQueryClient } from '@tanstack/react-query';
 import { Outlet, useLocation } from 'react-router-dom';
 
@@ -19,7 +20,7 @@ const Layout = () => {
     location.pathname.startsWith(ROUTES_CONFIG.onboardingCallback.path);
 
   const isSidebarHidden = isAuthPage || isPolicyPage;
-  const isLoggedIn = !!localStorage.getItem('token');
+  const isLoggedIn = authStorage.hasAccessToken();
 
   const { data: hasJobData, isLoading: isHasJobLoading } = useGetHasJob(
     isLoggedIn && !isAuthPage
diff --git a/apps/client/src/pages/onBoarding/GoogleCallback.tsx b/apps/client/src/pages/onBoarding/GoogleCallback.tsx
index 0a872de4..a742e7fe 100644
--- a/apps/client/src/pages/onBoarding/GoogleCallback.tsx
+++ b/apps/client/src/pages/onBoarding/GoogleCallback.tsx
@@ -1,18 +1,10 @@
 import apiRequest from '@shared/apis/setting/axiosInstance';
 import LoadingChippi from '@shared/components/loadingChippi/LoadingChippi';
+import { authStorage } from '@shared/utils/authStorage';
+import { extensionBridge } from '@shared/utils/extensionBridge';
 import { useEffect } from 'react';
 import { useNavigate, useSearchParams } from 'react-router-dom';
 
-const sendTokenToExtension = (token: string) => {
-  window.postMessage(
-    {
-      type: 'SET_TOKEN',
-      token,
-    },
-    window.location.origin
-  );
-};
-
 const GoogleCallback = () => {
   const navigate = useNavigate();
   const [searchParams] = useSearchParams();
@@ -37,16 +29,16 @@ const GoogleCallback = () => {
   ) => {
     if (isUser) {
       if (accessToken) {
-        localStorage.setItem('token', accessToken);
-        sendTokenToExtension(accessToken);
+        authStorage.setAccessToken(accessToken);
+        extensionBridge.syncToken(accessToken);
       }
 
       if (refreshToken) {
-        localStorage.setItem('refreshToken', refreshToken);
+        authStorage.setRefreshToken(refreshToken);
       }
 
       if (typeof hasJob === 'boolean') {
-        localStorage.setItem('hasJob', String(hasJob));
+        authStorage.setHasJob(hasJob);
       }
       navigate('/');
     } else {
@@ -74,8 +66,7 @@ const GoogleCallback = () => {
       const { isUser, userId, email, accessToken, refreshToken, hasJob } =
         res.data.data;
 
-      localStorage.setItem('email', email);
-      localStorage.setItem('userId', userId);
+      authStorage.setUserIdentity(email, userId);
 
       handleUserLogin(isUser, accessToken, refreshToken, hasJob);
     } catch (error) {
diff --git a/apps/client/src/shared/apis/queries.ts b/apps/client/src/shared/apis/queries.ts
index 7e2a37ba..e4e1d2b9 100644
--- a/apps/client/src/shared/apis/queries.ts
+++ b/apps/client/src/shared/apis/queries.ts
@@ -29,6 +29,8 @@ import {
   JobsResponse,
 } from '@shared/types/api';
 import { fetchOGData } from '@shared/utils/fetchOgData';
+import { authStorage } from '@shared/utils/authStorage';
+import { extensionBridge } from '@shared/utils/extensionBridge';
 import {
   useMutation,
   UseMutationResult,
@@ -94,17 +96,8 @@ export const usePostSignUp = () => {
       const newToken = data?.data?.token || data?.token;
 
       if (newToken) {
-        localStorage.setItem('token', newToken);
-        const sendTokenToExtension = (token: string) => {
-          window.postMessage(
-            {
-              type: 'SET_TOKEN',
-              token,
-            },
-            window.location.origin
-          );
-        };
-        sendTokenToExtension(newToken);
+        authStorage.setAccessToken(newToken);
+        extensionBridge.syncToken(newToken);
       }
     },
     onError: (error) => {
diff --git a/apps/client/src/shared/apis/setting/axiosInstance.ts b/apps/client/src/shared/apis/setting/axiosInstance.ts
index b79cabb4..1998afce 100644
--- a/apps/client/src/shared/apis/setting/axiosInstance.ts
+++ b/apps/client/src/shared/apis/setting/axiosInstance.ts
@@ -1,4 +1,34 @@
 import axios from 'axios';
+import { authStorage } from '@shared/utils/authStorage';
+import { extensionBridge } from '@shared/utils/extensionBridge';
+
+const noAuthNeeded = [
+  '/api/v1/auth/token',
+  '/api/v3/auth/signup',
+  '/api/v3/auth/google',
+  '/api/v3/auth/reissue',
+];
+
+const reissueToken = async () => {
+  return await axios.post(
+    `${import.meta.env.VITE_BASE_URL}/api/v3/auth/reissue`,
+    {},
+    {
+      withCredentials: true,
+    }
+  );
+};
+
+const syncAccessToken = (token: string) => {
+  authStorage.setAccessToken(token);
+  extensionBridge.syncToken(token);
+};
+
+const clearAuthSessionAndRedirect = () => {
+  authStorage.clearSession();
+  extensionBridge.logout();
+  window.location.href = '/onboarding?step=SOCIAL_LOGIN';
+};
 
 // Axios 인스턴스
 const apiRequest = axios.create({
@@ -10,7 +40,7 @@ const apiRequest = axios.create({
 
 // 요청 인터셉터
 apiRequest.interceptors.request.use(async (config) => {
-  const token = localStorage.getItem('token');
+  const token = authStorage.getAccessToken();
 
   if (token) {
     config.headers.Authorization = `Bearer ${token}`;
@@ -25,13 +55,6 @@ apiRequest.interceptors.response.use(
   async (error) => {
     const originalRequest = error.config;
 
-    const noAuthNeeded = [
-      '/api/v1/auth/token',
-      '/api/v3/auth/signup',
-      '/api/v3/auth/google',
-      '/api/v3/auth/reissue',
-    ];
-
     const isNoAuth = noAuthNeeded.some((url) =>
       originalRequest.url?.includes(url)
     );
@@ -48,30 +71,21 @@ apiRequest.interceptors.response.use(
       originalRequest._retry = true;
 
       try {
-        const res = await axios.post(
-          `${import.meta.env.VITE_BASE_URL}/api/v3/auth/reissue`,
-          {},
-          {
-            withCredentials: true,
-          }
-        );
-
-        const newAccessToken = res.data.data.token;
-        localStorage.setItem('token', newAccessToken);
-
-        window.postMessage(
-          { type: 'SET_TOKEN', token: newAccessToken },
-          window.location.origin
-        );
+        const res = await reissueToken();
+        const newAccessToken = res.data?.data?.token;
+
+        if (!newAccessToken) {
+          throw new Error('토큰 재발급 응답에 access token이 없습니다.');
+        }
 
+        syncAccessToken(newAccessToken);
+        originalRequest.headers = originalRequest.headers ?? {};
         originalRequest.headers.Authorization = `Bearer ${newAccessToken}`;
         return apiRequest(originalRequest);
       } catch (reissueError) {
         console.error('토큰 재발급 실패. 다시 로그인해주세요.', reissueError);
 
-        localStorage.removeItem('token');
-        localStorage.removeItem('refreshToken');
-        window.location.href = '/onboarding?step=SOCIAL_LOGIN';
+        clearAuthSessionAndRedirect();
 
         return Promise.reject(reissueError);
       }
diff --git a/apps/client/src/shared/components/profilePopup/ProfilePopup.tsx b/apps/client/src/shared/components/profilePopup/ProfilePopup.tsx
index 4206d722..7ea92d7d 100644
--- a/apps/client/src/shared/components/profilePopup/ProfilePopup.tsx
+++ b/apps/client/src/shared/components/profilePopup/ProfilePopup.tsx
@@ -2,6 +2,8 @@ import { Icon } from '@pinback/design-system/icons';
 import { Button } from '@pinback/design-system/ui';
 import { useQueryClient } from '@tanstack/react-query';
 import formatRemindTime from '@shared/utils/formatRemindTime';
+import { authStorage } from '@shared/utils/authStorage';
+import { extensionBridge } from '@shared/utils/extensionBridge';
 import { useEffect, useRef } from 'react';
 import { useNavigate } from 'react-router-dom';
 
@@ -42,19 +44,9 @@ export default function ProfilePopup({
   if (!open) return null;
 
   const handleLogout = () => {
-    localStorage.removeItem('token');
-    localStorage.removeItem('email');
-    localStorage.removeItem('userId');
+    authStorage.clearSession();
     queryClient.clear();
-    const sendExtensionLogout = () => {
-      window.postMessage(
-        {
-          type: 'Extension-Logout',
-        },
-        window.location.origin
-      );
-    };
-    sendExtensionLogout();
+    extensionBridge.logout();
     navigate('/login');
   };
 
diff --git a/apps/client/src/shared/utils/authStorage.ts b/apps/client/src/shared/utils/authStorage.ts
new file mode 100644
index 00000000..1ffafc66
--- /dev/null
+++ b/apps/client/src/shared/utils/authStorage.ts
@@ -0,0 +1,27 @@
+const AUTH_STORAGE_KEYS = {
+  token: 'token',
+  refreshToken: 'refreshToken',
+  email: 'email',
+  userId: 'userId',
+  hasJob: 'hasJob',
+} as const;
+
+export const authStorage = {
+  getAccessToken: () => localStorage.getItem(AUTH_STORAGE_KEYS.token),
+  hasAccessToken: () => !!localStorage.getItem(AUTH_STORAGE_KEYS.token),
+  setAccessToken: (token: string) =>
+    localStorage.setItem(AUTH_STORAGE_KEYS.token, token),
+  setRefreshToken: (refreshToken: string) =>
+    localStorage.setItem(AUTH_STORAGE_KEYS.refreshToken, refreshToken),
+  setHasJob: (hasJob: boolean) =>
+    localStorage.setItem(AUTH_STORAGE_KEYS.hasJob, String(hasJob)),
+  setUserIdentity: (email: string, userId: string) => {
+    localStorage.setItem(AUTH_STORAGE_KEYS.email, email);
+    localStorage.setItem(AUTH_STORAGE_KEYS.userId, userId);
+  },
+  clearSession: () => {
+    Object.values(AUTH_STORAGE_KEYS).forEach((key) => {
+      localStorage.removeItem(key);
+    });
+  },
+};
diff --git a/apps/client/src/shared/utils/extensionBridge.ts b/apps/client/src/shared/utils/extensionBridge.ts
new file mode 100644
index 00000000..fb5f74ab
--- /dev/null
+++ b/apps/client/src/shared/utils/extensionBridge.ts
@@ -0,0 +1,21 @@
+import { EXTENSION_MESSAGE_TYPE } from '@pinback/contracts/extension-messages';
+
+export const extensionBridge = {
+  syncToken: (token: string) => {
+    window.postMessage(
+      {
+        type: EXTENSION_MESSAGE_TYPE.setToken,
+        token,
+      },
+      window.location.origin
+    );
+  },
+  logout: () => {
+    window.postMessage(
+      {
+        type: EXTENSION_MESSAGE_TYPE.logout,
+      },
+      window.location.origin
+    );
+  },
+};
diff --git a/apps/extension/package.json b/apps/extension/package.json
index 34a444b9..f1f7715f 100644
--- a/apps/extension/package.json
+++ b/apps/extension/package.json
@@ -11,6 +11,7 @@
     "zip": "vite build && node scripts/zip.mjs"
   },
   "dependencies": {
+    "@pinback/contracts": "workspace:*",
     "@tanstack/react-query": "^5.85.5",
     "axios": "^1.11.0",
     "react": "^19.1.1",
diff --git a/apps/extension/src/background.ts b/apps/extension/src/background.ts
index 16530b84..42b17fcd 100644
--- a/apps/extension/src/background.ts
+++ b/apps/extension/src/background.ts
@@ -1,3 +1,5 @@
+import { EXTENSION_MESSAGE_TYPE } from '@pinback/contracts/extension-messages';
+
 chrome.runtime.onInstalled.addListener((details) => {
   if (details.reason === 'install') {
     chrome.identity.getProfileUserInfo(function (info) {
@@ -14,7 +16,7 @@ chrome.runtime.onInstalled.addListener((details) => {
 });
 
 chrome.runtime.onMessage.addListener((message) => {
-  if (message.type === 'SET_TOKEN') {
+  if (message.type === EXTENSION_MESSAGE_TYPE.setToken) {
     chrome.storage.local.set({ token: message.token }, () => {
       console.log('Token saved!');
     });
@@ -22,7 +24,7 @@ chrome.runtime.onMessage.addListener((message) => {
 });
 
 chrome.runtime.onMessage.addListener((message) => {
-  if (message.type === 'Extension-Logout') {
+  if (message.type === EXTENSION_MESSAGE_TYPE.logout) {
     chrome.storage.local.remove('token', () => {
       console.log('Token removed!');
     });
diff --git a/apps/extension/src/content.ts b/apps/extension/src/content.ts
index 490c2e3f..92002d60 100644
--- a/apps/extension/src/content.ts
+++ b/apps/extension/src/content.ts
@@ -1,8 +1,10 @@
+import { EXTENSION_MESSAGE_TYPE } from '@pinback/contracts/extension-messages';
+
 window.addEventListener('message', (event) => {
   if (event.source !== window) return;
-  if (event.data.type === 'SET_TOKEN') {
+  if (event.data.type === EXTENSION_MESSAGE_TYPE.setToken) {
     chrome.runtime.sendMessage({
-      type: 'SET_TOKEN',
+      type: EXTENSION_MESSAGE_TYPE.setToken,
       token: event.data.token,
     });
     chrome.storage.local.set({ token: event.data.token }, () => {
@@ -13,7 +15,7 @@ window.addEventListener('message', (event) => {
 
 window.addEventListener('message', (event) => {
   if (event.source !== window) return;
-  if (event.data.type === 'Extension-Logout') {
+  if (event.data.type === EXTENSION_MESSAGE_TYPE.logout) {
     chrome.storage.local.remove('token', () => {
       console.log('Token removed!');
     });
diff --git a/packages/contracts/package.json b/packages/contracts/package.json
new file mode 100644
index 00000000..8f66219d
--- /dev/null
+++ b/packages/contracts/package.json
@@ -0,0 +1,16 @@
+{
+  "name": "@pinback/contracts",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "exports": {
+    "./extension-messages": "./src/extension-messages.ts"
+  },
+  "scripts": {
+    "check-types": "tsc --noEmit"
+  },
+  "devDependencies": {
+    "@pinback/typescript-config": "workspace:*",
+    "typescript": "5.9.2"
+  }
+}
diff --git a/packages/contracts/src/extension-messages.ts b/packages/contracts/src/extension-messages.ts
new file mode 100644
index 00000000..ef9ef2a7
--- /dev/null
+++ b/packages/contracts/src/extension-messages.ts
@@ -0,0 +1,16 @@
+export const EXTENSION_MESSAGE_TYPE = {
+  setToken: 'SET_TOKEN',
+  logout: 'Extension-Logout',
+} as const;
+
+export type ExtensionMessageType =
+  (typeof EXTENSION_MESSAGE_TYPE)[keyof typeof EXTENSION_MESSAGE_TYPE];
+
+export type ExtensionMessage =
+  | {
+      type: typeof EXTENSION_MESSAGE_TYPE.setToken;
+      token: string;
+    }
+  | {
+      type: typeof EXTENSION_MESSAGE_TYPE.logout;
+    };
diff --git a/packages/contracts/tsconfig.json b/packages/contracts/tsconfig.json
new file mode 100644
index 00000000..9fa8bc1f
--- /dev/null
+++ b/packages/contracts/tsconfig.json
@@ -0,0 +1,10 @@
+{
+  "extends": "../typescript-config/base.json",
+  "compilerOptions": {
+    "rootDir": ".",
+    "baseUrl": ".",
+    "lib": ["ES2022"]
+  },
+  "include": ["src"],
+  "exclude": ["node_modules", "dist"]
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index fe006cc3..205b3994 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -90,6 +90,9 @@ importers:
 
   apps/client:
     dependencies:
+      '@pinback/contracts':
+        specifier: workspace:*
+        version: link:../../packages/contracts
       '@tanstack/react-query':
         specifier: ^5.85.3
         version: 5.85.5(react@19.1.1)
@@ -184,6 +187,9 @@ importers:
 
   apps/extension:
     dependencies:
+      '@pinback/contracts':
+        specifier: workspace:*
+        version: link:../../packages/contracts
       '@tanstack/react-query':
         specifier: ^5.85.5
         version: 5.85.5(react@19.1.1)
@@ -346,6 +352,15 @@ importers:
         specifier: ^5.1.4
         version: 5.1.4(typescript@5.8.3)(vite@7.1.2(@types/node@22.15.3)(jiti@2.5.1)(lightningcss@1.30.1)(tsx@4.20.4)(yaml@2.8.1))
 
+  packages/contracts:
+    devDependencies:
+      '@pinback/typescript-config':
+        specifier: workspace:*
+        version: link:../typescript-config
+      typescript:
+        specifier: 5.9.2
+        version: 5.9.2
+
   packages/design-system:
     dependencies:
       '@ncdai/react-wheel-picker':