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+---
+title: Use SWR for Automatic Deduplication
+impact: MEDIUM-HIGH
+impactDescription: automatic deduplication
+tags: client, swr, deduplication, data-fetching
+---
+
+## Use SWR for Automatic Deduplication
+
+SWR enables request deduplication, caching, and revalidation across component instances.
+
+**Incorrect (no deduplication, each instance fetches):**
+
+```tsx
+function UserList() {
+  const [users, setUsers] = useState([]);
+  useEffect(() => {
+    fetch("/api/users")
+      .then((r) => r.json())
+      .then(setUsers);
+  }, []);
+}
+```
+
+**Correct (multiple instances share one request):**
+
+```tsx
+import useSWR from "swr";
+
+function UserList() {
+  const { data: users } = useSWR("/api/users", fetcher);
+}
+```
+
+**For immutable data:**
+
+```tsx
+import { useImmutableSWR } from "@/lib/swr";
+
+function StaticContent() {
+  const { data } = useImmutableSWR("/api/config", fetcher);
+}
+```
+
+**For mutations:**
+
+```tsx
+import { useSWRMutation } from "swr/mutation";
+
+function UpdateButton() {
+  const { trigger } = useSWRMutation("/api/user", updateUser);
+  return <button onClick={() => trigger()}>Update</button>;
+}
+```
+
+Reference: [https://swr.vercel.app](https://swr.vercel.app)