diff --git a/src/features/home/api/search.ts b/src/features/home/api/search.ts
index d6e5558..7a9f22e 100644
--- a/src/features/home/api/search.ts
+++ b/src/features/home/api/search.ts
@@ -35,6 +35,6 @@ export const useSearchHistory = () => {
     onSuccess: () => {
       console.log("검색 히스토리 저장");
     },
-    onError: err => console.log(err),
+    // onError: err => console.log(err),
   });
 };
diff --git a/src/features/mypage/api/account.ts b/src/features/mypage/api/account.ts
index fb63ae0..3473d77 100644
--- a/src/features/mypage/api/account.ts
+++ b/src/features/mypage/api/account.ts
@@ -1,6 +1,10 @@
 import api from "@/shared/api/api";
 import { API_ENDPOINTS } from "@/shared/consts/endpoints";
+import { USER_ERROR } from "@/shared/consts/errorCodes";
 import { useMutation } from "@tanstack/react-query";
+import { toast } from "react-toastify";
+import type { AxiosError } from "axios";
+import useUserStore from "@/shared/model/useUserStore";
 
 export const deleteAccount = async () => {
   const { data } = await api.patch(API_ENDPOINTS.users.me.withdrawal);
@@ -8,9 +12,14 @@ export const deleteAccount = async () => {
 };
 
 export const useDeleteAccount = (onSuccess: () => void) => {
-  return useMutation({
+  return useMutation<unknown, AxiosError<{ code: string; message: string }>>({
     mutationFn: deleteAccount,
     onSuccess: () => onSuccess?.(),
-    onError: err => console.error(err),
+    onError: e => {
+      if (e?.response?.data?.code === USER_ERROR.ALREADY_WITHDRAWN) {
+        toast.error(e.response.data.message);
+        useUserStore.getState().logout();
+      }
+    },
   });
 };
diff --git a/src/features/mypage/api/myEdit.ts b/src/features/mypage/api/myEdit.ts
index b9d7809..7ac3169 100644
--- a/src/features/mypage/api/myEdit.ts
+++ b/src/features/mypage/api/myEdit.ts
@@ -9,6 +9,9 @@ import { API_ENDPOINTS } from "@/shared/consts/endpoints";
 import { SHARED_QUERY_KEY } from "@/shared/consts/queryKeys";
 import { HOME_QUERY_KEY } from "@/features/home/consts/queryKeys";
 import { useMutation, useQueryClient } from "@tanstack/react-query";
+import { USER_ERROR } from "@/shared/consts/errorCodes";
+import { toast } from "react-toastify";
+import type { AxiosError } from "axios";
 
 // 내 관심사 수정 =>mypage
 export const putMyInterst = async (body: InterestDataDto) => {
@@ -25,7 +28,12 @@ export const usePutMyInterst = () => {
     HOME_QUERY_KEY.POSTS_RECOMMEND,
   ] as const;
 
-  return useMutation({
+  return useMutation<
+    unknown,
+    AxiosError<{ code: string; message: string }>,
+    InterestDataDto,
+    { previous: InterestTypeDto[] | undefined; previousRecommend: unknown }
+  >({
     mutationFn: (body: InterestDataDto) => putMyInterst(body),
 
     onMutate: async (payload: InterestDataDto) => {
@@ -43,7 +51,11 @@ export const usePutMyInterst = () => {
 
       return { previous, previousRecommend };
     },
-    onError: (_err, _payload, context) => {
+    onError: (e, _, context) => {
+      if (e?.response?.data?.code == USER_ERROR.INVALID_INTEREST) {
+        toast.error(e.response.data.message);
+      }
+
       if (context?.previous) {
         queryClient.setQueryData(queryKey, context.previous);
       }
@@ -78,6 +90,5 @@ export const usePatchMyProfile = (onSuccess?: () => void) => {
       });
       onSuccess?.();
     },
-    onError: err => console.log(err),
   });
 };
diff --git a/src/features/onboarding/api/onboarding.ts b/src/features/onboarding/api/onboarding.ts
index af1b662..25a2ce5 100644
--- a/src/features/onboarding/api/onboarding.ts
+++ b/src/features/onboarding/api/onboarding.ts
@@ -1,8 +1,11 @@
 import { useMutation } from "@tanstack/react-query";
 import { useNavigate } from "react-router-dom";
+import type { AxiosError } from "axios";
 import api from "@/shared/api/api";
 import { API_ENDPOINTS } from "@/shared/consts/endpoints";
 import type { OnboardingRequestType } from "./onboarding.types";
+import { USER_ERROR } from "@/shared/consts/errorCodes";
+import { toast } from "react-toastify";
 
 export const postOnboarding = async (body: OnboardingRequestType) => {
   const res = await api.post(API_ENDPOINTS.onboarding.complete, body);
@@ -12,9 +15,17 @@ export const postOnboarding = async (body: OnboardingRequestType) => {
 export const useSubmitOnboarding = () => {
   const navigate = useNavigate();
 
-  return useMutation({
+  return useMutation<
+    unknown,
+    AxiosError<{ code: string; message: string }>,
+    OnboardingRequestType
+  >({
     mutationFn: (body: OnboardingRequestType) => postOnboarding(body),
     onSuccess: () => navigate("/"),
-    onError: err => console.log(err),
+    onError: err => {
+      if (err.response?.data.code === USER_ERROR.INVALID_INTEREST) {
+        toast.error(err.response.data.message);
+      }
+    },
   });
 };
diff --git a/src/main.tsx b/src/main.tsx
index d52e33d..4bcaa17 100644
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -1,7 +1,7 @@
 import { StrictMode } from "react";
 import { createRoot } from "react-dom/client";
 import "@/app/styles/index.css";
-import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { QueryClient, QueryClientProvider, MutationCache } from "@tanstack/react-query";
 import axios from "axios";
 import { ReactQueryDevtools } from "@tanstack/react-query-devtools";
 import { ThemeProvider } from "@/app/providers/ThemProvider.tsx";
@@ -9,16 +9,30 @@ import { HelmetProvider } from "react-helmet-async";
 import App from "@/app/App";
 import router from "@/app/routes";
 import { initGlobalNavigate } from "@/shared/lib/globalNavigate";
+import { toast } from "react-toastify";
 
 initGlobalNavigate((path) => router.navigate(path));
 
+const isServerError = (error: unknown) =>
+  axios.isAxiosError(error) &&
+  (error.response?.status === 500 || error.response?.status === 503);
+
 const queryClient = new QueryClient({
+  mutationCache: new MutationCache({
+    onError: (error) => {
+      if (isServerError(error)) {
+        toast.error("서버에 문제가 발생했습니다. 잠시 후 다시 시도해주세요.");
+      }
+    },
+  }),
   defaultOptions: {
     queries: {
       retry: (failureCount, error) => {
         if (axios.isAxiosError(error) && !error.response) return false;
+        if (isServerError(error)) return false;
         return failureCount < 3;
       },
+      throwOnError: (error) => isServerError(error),
     },
   },
 });
diff --git a/src/mocks/handlers.ts b/src/mocks/handlers.ts
index a658a01..8eda461 100644
--- a/src/mocks/handlers.ts
+++ b/src/mocks/handlers.ts
@@ -1,9 +1,10 @@
-import { http, HttpResponse } from "msw";
+import { http, HttpResponse, passthrough } from "msw";
 import {
   AUTH_ERROR,
-  ACTIVITY_ERROR,
-  USER_ERROR,
+  BOOKMARK_ERROR,
   POST_ERROR,
+  READPOST_ERROR,
+  USER_ERROR,
   COMMON_ERROR,
 } from "@/shared/consts/errorCodes";
 
@@ -44,23 +45,37 @@ export const scenarioAuth = {
 
 /** 북마크 에러 시나리오 */
 export const scenarioBookmark = {
-  /** 북마크 추가 => 이미 북마크한 게시글 */
+  // POST /api/v1/activities/bookmarks
+  /** 북마크 추가 => 이미 북마크한 게시글 (BOOKMARK409_1) */
   alreadyBookmarked: http.post(url("/api/v1/activities/bookmarks"), () =>
-    err(ACTIVITY_ERROR.ALREADY_BOOKMARKED, "이미 북마크한 게시글입니다.", 409),
+    err(BOOKMARK_ERROR.ALREADY_BOOKMARKED, "이미 북마크한 게시글입니다.", 409),
+  ),
+  /** 북마크 추가 => 게시글을 찾을 수 없음 (POST404_1) */
+  postPostNotFound: http.post(url("/api/v1/activities/bookmarks"), () =>
+    err(POST_ERROR.NOT_FOUND, "게시글을 찾을 수 없습니다.", 404),
   ),
 
-  /** 북마크 삭제 => 북마크를 찾을 수 없음 */
+  // DELETE /api/v1/activities/bookmarks
+  /** 북마크 삭제 => 북마크를 찾을 수 없음 (BOOKMARK404_1) */
   bookmarkNotFound: http.delete(url("/api/v1/activities/bookmarks"), () =>
-    err(ACTIVITY_ERROR.BOOKMARK_NOT_FOUND, "북마크를 찾을 수 없습니다.", 404),
+    err(BOOKMARK_ERROR.BOOKMARK_NOT_FOUND, "북마크를 찾을 수 없습니다.", 404),
+  ),
+  /** 북마크 삭제 => 게시글을 찾을 수 없음 (POST404_1) */
+  deletePostNotFound: http.delete(url("/api/v1/activities/bookmarks"), () =>
+    err(POST_ERROR.NOT_FOUND, "게시글을 찾을 수 없습니다.", 404),
   ),
 };
 
-/** 게시글 에러 시나리오 */
-export const scenarioPost = {
-  /** 게시글 조회 => 찾을 수 없음 */
-  notFound: http.get(url("/api/v2/posts/*"), () =>
+/** 읽은 게시글 에러 시나리오 (POST /api/v1/activities/read-posts) */
+export const scenarioReadPost = {
+  /** 게시글을 찾을 수 없음 (POST404_1) */
+  postNotFound: http.post(url("/api/v1/activities/read-posts"), () =>
     err(POST_ERROR.NOT_FOUND, "게시글을 찾을 수 없습니다.", 404),
   ),
+  /** 조회수 증가 실패 (READ_POST500_1) — 전역 toast 동작 확인 */
+  readPostFailed: http.post(url("/api/v1/activities/read-posts"), () =>
+    err(READPOST_ERROR.READ_POST, "조회수 증가에 실패했습니다.", 500),
+  ),
 };
 
 /** 유저 에러 시나리오 */
@@ -83,8 +98,8 @@ export const scenarioUser = {
 
 /** 공통 에러 시나리오 */
 export const scenarioCommon = {
-  /** 서버 에러 */
-  internalServer: http.get(url("/api/*"), () =>
+  /** 서버 에러 (전체) — query: ErrorBoundary fallback / mutation: toast */
+  internalServer: http.all(url("/api/*"), () =>
     err(
       COMMON_ERROR.INTERNAL_SERVER,
       "서버 에러, 관리자에게 문의 바랍니다.",
@@ -92,8 +107,50 @@ export const scenarioCommon = {
     ),
   ),
 
-  /** 서비스 점검 */
-  serviceUnavailable: http.get(url("/api/*"), () =>
+  /** 서버 에러 (query만) — GET만 막아 mutation은 정상 동작 */
+  internalServerQuery: http.get(url("/api/*"), () =>
+    err(
+      COMMON_ERROR.INTERNAL_SERVER,
+      "서버 에러, 관리자에게 문의 바랍니다.",
+      500,
+    ),
+  ),
+
+  /** 서버 에러 (mutation만) — POST/PATCH/DELETE만 막아 query는 정상 동작 */
+  internalServerMutation: [
+    http.post(url("/api/v1/auth/refresh"), () => passthrough()),
+    http.post(url("/api/*"), () =>
+      err(
+        COMMON_ERROR.INTERNAL_SERVER,
+        "서버 에러, 관리자에게 문의 바랍니다.",
+        500,
+      ),
+    ),
+    http.patch(url("/api/*"), () =>
+      err(
+        COMMON_ERROR.INTERNAL_SERVER,
+        "서버 에러, 관리자에게 문의 바랍니다.",
+        500,
+      ),
+    ),
+    http.delete(url("/api/*"), () =>
+      err(
+        COMMON_ERROR.INTERNAL_SERVER,
+        "서버 에러, 관리자에게 문의 바랍니다.",
+        500,
+      ),
+    ),
+    http.put(url("/api/*"), () =>
+      err(
+        COMMON_ERROR.INTERNAL_SERVER,
+        "서버 에러, 관리자에게 문의 바랍니다.",
+        500,
+      ),
+    ),
+  ],
+
+  /** 서비스 점검 — query: ErrorBoundary fallback / mutation: toast */
+  serviceUnavailable: http.all(url("/api/*"), () =>
     err(
       COMMON_ERROR.SERVICE_UNAVAILABLE,
       "서버가 일시적으로 사용중지 되었습니다.",
@@ -115,18 +172,24 @@ export const scenarioNetwork = {
 
 export const handlers = [
   // 인증
-  // scenarioAuth.refreshMismatch,   // 401: refresh 불일치 => 즉시 로그아웃 확인
-  // scenarioAuth.withdrawn, // 403: 탈퇴 회원 => 즉시 로그아웃 확인
-  // 북마크
-  // scenarioBookmark.alreadyBookmarked, // 409: 중복 북마크
-  // scenarioBookmark.bookmarkNotFound,  // 404: 북마크 없음
+  // scenarioAuth.refreshMismatch,         // 401: refresh 불일치 => 즉시 로그아웃 -O
+  // scenarioAuth.withdrawn,               // 403: 탈퇴 회원 => 즉시 로그아웃 -O
+  // 북마크 POST
+  // scenarioBookmark.alreadyBookmarked,   // 409: 중복 북마크 -O
+  // scenarioBookmark.postPostNotFound,    // 404: 게시글 없음
+  // 북마크 DELETE
+  // scenarioBookmark.bookmarkNotFound,    // 404: 북마크 없음 -O
+  // scenarioBookmark.deletePostNotFound,  // 404: 게시글 없음
+  // 읽은 게시글 POST
+  // scenarioReadPost.postNotFound,        // 404: 게시글 없음
+  // scenarioReadPost.readPostFailed,      // 500: 조회수 증가 실패 => 전역 toast -O
   // 유저
-  // scenarioUser.invalidInterest,   // 400: 유효하지 않은 관심사
-  // scenarioUser.alreadyWithdrawn, // 400: 이미 탈퇴한 회원
+  // scenarioUser.invalidInterest,            // 400: 유효하지 않은 관심사
+  // scenarioUser.alreadyWithdrawn,        // 400: 이미 탈퇴한 회원 -O
   // 공통
-  // scenarioCommon.internalServer,       // 500: 서버 에러
-  // scenarioCommon.serviceUnavailable,   // 503: 서비스 점검
+  // scenarioCommon.internalServer,        // 500: 서버 에러
+  // ...scenarioCommon.internalServerMutation,
+  // scenarioCommon.serviceUnavailable,    // 503: 서비스 점검
   // 네트워크
-  // scenarioNetwork.offline, // 연결 끊김 (ERR_NETWORK)
-  // scenarioNetwork.bookmarkOffline,// 북마크 API만 연결 끊김
+  // scenarioNetwork.offline,              // 연결 끊김 (ERR_NETWORK) -O
 ];
diff --git a/src/shared/api/activity.ts b/src/shared/api/activity.ts
index c58ef0a..26bca7b 100644
--- a/src/shared/api/activity.ts
+++ b/src/shared/api/activity.ts
@@ -1,12 +1,13 @@
 import { useMutation, useQueryClient } from "@tanstack/react-query";
+import type { QueryKey } from "@tanstack/react-query";
+import type { AxiosError } from "axios";
 import type { ActivityPostType, ReadPostType } from "./activity.types";
 import api from "./api";
 import { SHARED_QUERY_KEY } from "../consts/queryKeys";
 import { updateBookmarkState } from "../lib/updateBookmarkState";
-import {
-  API_ENDPOINTS,
-  getActivityPostsEndpoint,
-} from "../consts/endpoints";
+import { API_ENDPOINTS, getActivityPostsEndpoint } from "../consts/endpoints";
+import { BOOKMARK_ERROR, POST_ERROR } from "@/shared/consts/errorCodes";
+import { toast } from "react-toastify";
 
 export type { ActivityPostType };
 
@@ -21,7 +22,12 @@ export const usePostBookmark = () => {
   const queryClient = useQueryClient();
   const postsQueryKey = [SHARED_QUERY_KEY.POSTS] as const;
 
-  return useMutation({
+  return useMutation<
+    unknown,
+    AxiosError<{ code: string; message: string }>,
+    number,
+    { previousQueries: [QueryKey, unknown][] }
+  >({
     mutationFn: (postId: number) => postBookmark(postId),
     onMutate: async postId => {
       await queryClient.cancelQueries({ queryKey: postsQueryKey });
@@ -37,8 +43,19 @@ export const usePostBookmark = () => {
 
       return { previousQueries };
     },
-    onError: () =>
-      queryClient.invalidateQueries({ queryKey: postsQueryKey }),
+    onError: (e, _, context) => {
+      const code = e?.response?.data?.code;
+      if (
+        code === BOOKMARK_ERROR.ALREADY_BOOKMARKED ||
+        code === POST_ERROR.NOT_FOUND
+      ) {
+        toast.error(e.response?.data.message);
+      }
+      context?.previousQueries.forEach(([queryKey, data]) => {
+        queryClient.setQueryData(queryKey, data);
+      });
+      queryClient.invalidateQueries({ queryKey: postsQueryKey });
+    },
   });
 };
 
@@ -53,7 +70,12 @@ export const useDeleteBookmark = () => {
   const queryClient = useQueryClient();
   const postsQueryKey = [SHARED_QUERY_KEY.POSTS] as const;
 
-  return useMutation({
+  return useMutation<
+    unknown,
+    AxiosError<{ code: string; message: string }>,
+    number,
+    { previousQueries: [QueryKey, unknown][] }
+  >({
     mutationFn: (postId: number) => deleteBookmark(postId),
     onMutate: async postId => {
       await queryClient.cancelQueries({ queryKey: postsQueryKey });
@@ -68,8 +90,19 @@ export const useDeleteBookmark = () => {
 
       return { previousQueries };
     },
-    onError: () =>
-      queryClient.invalidateQueries({ queryKey: postsQueryKey }),
+    onError: (e, _, context) => {
+      const code = e?.response?.data?.code;
+      if (
+        code === BOOKMARK_ERROR.BOOKMARK_NOT_FOUND ||
+        code === POST_ERROR.NOT_FOUND
+      ) {
+        toast.error(e.response?.data.message);
+      }
+      context?.previousQueries.forEach(([queryKey, data]) => {
+        queryClient.setQueryData(queryKey, data);
+      });
+      queryClient.invalidateQueries({ queryKey: postsQueryKey });
+    },
   });
 };
 
@@ -103,13 +136,20 @@ export const usePostReadPost = () => {
   const queryClient = useQueryClient();
   const postsQueryKey = [SHARED_QUERY_KEY.POSTS] as const;
 
-  return useMutation({
+  return useMutation<
+    unknown,
+    AxiosError<{ code: string; message: string }>,
+    ReadPostType
+  >({
     mutationFn: (body: ReadPostType) => postReadPosts(body),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: postsQueryKey });
     },
-    onError: err => {
-      console.log(err);
+    onError: e => {
+      const code = e?.response?.data?.code;
+      if (code === POST_ERROR.NOT_FOUND) {
+        toast.error(e.response?.data.message);
+      }
     },
   });
 };
diff --git a/src/shared/consts/errorCodes.ts b/src/shared/consts/errorCodes.ts
index fc8d18b..667ff93 100644
--- a/src/shared/consts/errorCodes.ts
+++ b/src/shared/consts/errorCodes.ts
@@ -1,38 +1,15 @@
 // 공통 error
 
 export const COMMON_ERROR = {
-  BAD_REQUEST: "COMMON400",
-  VALIDATION: "COMMON400_VALIDATION",
-  TYPE: "COMMON400_TYPE",
-  FORMAT: "COMMON400_FORMAT",
-  PARAM: "COMMON400_PARAM",
-  UNAUTHORIZED: "COMMON401",
-  FORBIDDEN: "COMMON403",
-  NOT_FOUND: "COMMON404",
   INTERNAL_SERVER: "COMMON500",
   SERVICE_UNAVAILABLE: "COMMON503",
 } as const;
 
 export const AUTH_ERROR = {
-  TYPE_MISMATCH: "AUTH400_TYPE_MISMATCH",
-  INVALID: "AUTH401_INVALID",
   EXPIRED: "AUTH401_EXPIRED",
-  MALFORMED: "AUTH401_MALFORMED",
-  SIGNATURE: "AUTH401_SIGNATURE",
-  UNSUPPORTED: "AUTH401_UNSUPPORTED",
-  EMPTY_CLAIMS: "AUTH401_EMPTY_CLAIMS",
-  INVALID_REFRESH: "AUTH401_INVALID_REFRESH",
-  REFRESH_MISSING: "AUTH401_REFRESH_MISSING",
   REFRESH_MISMATCH: "AUTH401_REFRESH_MISMATCH",
   KAKAO_TOKEN: "AUTH401_KAKAO_TOKEN",
   WITHDRAWN: "AUTH403_WITHDRAWN",
-  FORBIDDEN: "AUTH403_FORBIDDEN",
-  USER_NOT_FOUND: "AUTH404_USER",
-  KAKAO_API: "AUTH500_KAKAO_API",
-} as const;
-
-export const POST_ERROR = {
-  NOT_FOUND: "POST404_1",
 } as const;
 
 export const USER_ERROR = {
@@ -41,21 +18,32 @@ export const USER_ERROR = {
   NOT_FOUND: "USER404_1",
 } as const;
 
-export const ACTIVITY_ERROR = {
-  BOOKMARK_NOT_FOUND: "ACTIVITY404_1",
-  ALREADY_BOOKMARKED: "ACTIVITY409_1",
+export const BOOKMARK_ERROR = {
+  BOOKMARK_NOT_FOUND: "BOOKMARK404_1",
+  ALREADY_BOOKMARKED: "BOOKMARK409_1",
+} as const;
+
+export const POST_ERROR = {
+  NOT_FOUND: "POST404_1",
+} as const;
+
+export const READPOST_ERROR = {
+  READ_POST: "READ_POST500_1",
 } as const;
 
 export type CommonErrorCode = (typeof COMMON_ERROR)[keyof typeof COMMON_ERROR];
 export type AuthErrorCode = (typeof AUTH_ERROR)[keyof typeof AUTH_ERROR];
-export type PostErrorCode = (typeof POST_ERROR)[keyof typeof POST_ERROR];
 export type UserErrorCode = (typeof USER_ERROR)[keyof typeof USER_ERROR];
-export type ActivityErrorCode =
-  (typeof ACTIVITY_ERROR)[keyof typeof ACTIVITY_ERROR];
+export type BookmarkErrorCode =
+  (typeof BOOKMARK_ERROR)[keyof typeof BOOKMARK_ERROR];
+export type PostErrorCode = (typeof POST_ERROR)[keyof typeof POST_ERROR];
+export type ReadPostErrorCode =
+  (typeof READPOST_ERROR)[keyof typeof READPOST_ERROR];
 
 export type ErrorCode =
   | CommonErrorCode
   | AuthErrorCode
-  | PostErrorCode
   | UserErrorCode
-  | ActivityErrorCode;
+  | BookmarkErrorCode
+  | PostErrorCode
+  | ReadPostErrorCode;
diff --git a/src/shared/ui/ErrorBoundary.tsx b/src/shared/ui/ErrorBoundary.tsx
index ff301e3..2506cae 100644
--- a/src/shared/ui/ErrorBoundary.tsx
+++ b/src/shared/ui/ErrorBoundary.tsx
@@ -22,7 +22,7 @@ export const DefaultErrorFallback = ({
     <div className="min-h-dvh flex items-center justify-center pb-20">
       <div className="flex justify-center flex-col items-center font-assistive ">
         <CircleAlert className="size-36 mb-10" />
-        <p>"서버에 문제가 발생했습니다."</p>
+        <p>서버에 문제가 발생했습니다.</p>
         <p className="mb-5 ">잠시 후 다시 시도해주세요.</p>
 
         <Button