diff --git a/public/index.html b/public/index.html
index 00ac223..5fb6f3e 100644
--- a/public/index.html
+++ b/public/index.html
@@ -125,13 +125,13 @@
       el.channelSelect.value = state.selectedVoiceChannel;
       el.channelFilter.value = state.selectedTextChannel;
       applyActiveTab(state.activeTab);
+      if ((textChanged || textGuildChanged) && state.selectedTextChannel && state.selectedTextGuild) {
+        await apiRequest('/api/backlog-sync', {
+          method: 'POST',
+          body: JSON.stringify({ guildId: state.selectedTextGuild, channelId: state.selectedTextChannel }),
+        }).catch((error) => showError(`Backlog sync failed: ${error.message}`));
+      }
       if (textChanged || textGuildChanged || state.activeTab === 'text') {
-        if (state.selectedTextChannel && state.selectedTextGuild) {
-          await apiRequest('/api/backlog-sync', {
-            method: 'POST',
-            body: JSON.stringify({ guildId: state.selectedTextGuild, channelId: state.selectedTextChannel }),
-          }).catch((error) => showError(`Backlog sync failed: ${error.message}`));
-        }
         await fetchText().catch((error) => showError(error.message));
       }
       await reconcileListenState();
diff --git a/src/routes/syncRoutes.ts b/src/routes/syncRoutes.ts
index 981df0b..1a80597 100644
--- a/src/routes/syncRoutes.ts
+++ b/src/routes/syncRoutes.ts
@@ -6,6 +6,24 @@ import { createChildLogger } from "../logger";
 import { syncSelectedChannelBacklog } from "../moderation/backlogSync";
 
 const logger = createChildLogger("sync-routes");
+const BACKLOG_SYNC_COOLDOWN_MS = 5 * 60 * 1000;
+const recentBacklogSyncs = new Map<string, number>();
+
+export function shouldSkipRecentBacklogSync(
+  guildId: string,
+  channelId: string,
+  now = Date.now(),
+): boolean {
+  const key = `${guildId}:${channelId}`;
+  const lastSync = recentBacklogSyncs.get(key);
+  if (lastSync && now - lastSync < BACKLOG_SYNC_COOLDOWN_MS) return true;
+  recentBacklogSyncs.set(key, now);
+  return false;
+}
+
+export function clearRecentBacklogSyncs(): void {
+  recentBacklogSyncs.clear();
+}
 
 export function createSyncRoutes(client: Client): Router {
   const router = express.Router();
@@ -26,6 +44,17 @@ export function createSyncRoutes(client: Client): Router {
         );
       }
 
+      if (shouldSkipRecentBacklogSync(guildId, channelId)) {
+        logger.debug({ guildId, channelId }, "Skipping recent backlog sync");
+        res.json({
+          success: true,
+          channelId,
+          messagesSync: 0,
+          skipped: true,
+        });
+        return;
+      }
+
       logger.info({ guildId, channelId }, "Starting backlog sync");
 
       const count = await syncSelectedChannelBacklog(
@@ -43,6 +72,7 @@ export function createSyncRoutes(client: Client): Router {
         success: true,
         channelId,
         messagesSync: count,
+        skipped: false,
       });
     } catch (error) {
       next(error);
diff --git a/tests/routes/syncRoutes.test.ts b/tests/routes/syncRoutes.test.ts
index 5664017..2dc9eda 100644
--- a/tests/routes/syncRoutes.test.ts
+++ b/tests/routes/syncRoutes.test.ts
@@ -1,6 +1,10 @@
 import type { Request, Response } from "express";
 import { beforeEach, describe, expect, it, vi } from "vitest";
-import { createSyncRoutes } from "../../src/routes/syncRoutes";
+import {
+  clearRecentBacklogSyncs,
+  createSyncRoutes,
+  shouldSkipRecentBacklogSync,
+} from "../../src/routes/syncRoutes";
 
 const syncSelectedChannelBacklog = vi.hoisted(() => vi.fn());
 
@@ -11,6 +15,7 @@ vi.mock("../../src/moderation/backlogSync", () => ({
 describe("createSyncRoutes", () => {
   beforeEach(() => {
     syncSelectedChannelBacklog.mockReset();
+    clearRecentBacklogSyncs();
   });
 
   it("syncs the selected guild and channel from the request", async () => {
@@ -41,7 +46,52 @@ describe("createSyncRoutes", () => {
       success: true,
       channelId: "selected-channel",
       messagesSync: 3,
+      skipped: false,
     });
     expect(next).not.toHaveBeenCalled();
   });
+
+  it("skips repeated sync requests during the cooldown window", async () => {
+    expect(shouldSkipRecentBacklogSync("guild", "channel", 1000)).toBe(false);
+    expect(shouldSkipRecentBacklogSync("guild", "channel", 1001)).toBe(true);
+  });
+
+  it("allows repeated sync requests after the cooldown window", async () => {
+    expect(shouldSkipRecentBacklogSync("guild", "channel", 1000)).toBe(false);
+    expect(shouldSkipRecentBacklogSync("guild", "channel", 301001)).toBe(false);
+  });
+
+  it("does not call Discord backlog sync for repeated requests", async () => {
+    syncSelectedChannelBacklog.mockResolvedValue(3);
+    const router = createSyncRoutes({} as never);
+    const route = router.stack.find(
+      (layer) => layer.route?.path === "/backlog-sync",
+    );
+    const handler = route?.route?.stack[0]?.handle;
+
+    await handler?.(
+      {
+        body: { guildId: "selected-guild", channelId: "selected-channel" },
+      } as Request,
+      { json: vi.fn() } as unknown as Response,
+      vi.fn(),
+    );
+
+    const json = vi.fn();
+    await handler?.(
+      {
+        body: { guildId: "selected-guild", channelId: "selected-channel" },
+      } as Request,
+      { json } as unknown as Response,
+      vi.fn(),
+    );
+
+    expect(syncSelectedChannelBacklog).toHaveBeenCalledTimes(1);
+    expect(json).toHaveBeenCalledWith({
+      success: true,
+      channelId: "selected-channel",
+      messagesSync: 0,
+      skipped: true,
+    });
+  });
 });