diff --git a/src/lib/api.ts b/src/lib/api.ts
new file mode 100644
index 0000000..4576208
--- /dev/null
+++ b/src/lib/api.ts
@@ -0,0 +1,33 @@
+export type ApiError = {
+  message: string;
+  status: number;
+  details?: unknown;
+};
+
+export async function fetchJson<T>(input: RequestInfo | URL, init?: RequestInit): Promise<T> {
+  const res = await fetch(input, {
+    headers: { "Content-Type": "application/json", ...(init?.headers ?? {}) },
+    ...init,
+  });
+  const text = await res.text();
+  const data = text ? safeJson(text) : undefined;
+  if (!res.ok) {
+    const err: ApiError = {
+      message: (data as any)?.error || res.statusText || "Request failed",
+      status: res.status,
+      details: data,
+    };
+    throw err;
+  }
+  return (data as T) ?? ({} as T);
+}
+
+function safeJson(text: string): unknown {
+  try {
+    return JSON.parse(text);
+  } catch {
+    return text;
+  }
+}
+
+
diff --git a/todolist.txt b/todolist.txt
index 68aa784..570a9c3 100644
--- a/todolist.txt
+++ b/todolist.txt
@@ -22,7 +22,7 @@
 
 [상태관리/데이터]
 4.1 React Query 설치 및 Provider 구성 o
-4.2 공통 fetcher/에러 형식/재시도·백오프 설정
+4.2 공통 fetcher/에러 형식/재시도·백오프 설정 o
 4.3 캐시 키/무효화 전략 수립 및 적용
 4.4 낙관적 업데이트 패턴 적용(작성/수정)