diff --git a/apps/planner/app/lib/metrics.server.ts b/apps/planner/app/lib/metrics.server.ts
index 85590c6..46d2060 100644
--- a/apps/planner/app/lib/metrics.server.ts
+++ b/apps/planner/app/lib/metrics.server.ts
@@ -1,29 +1,44 @@
 import client from "prom-client";
 
-// Collect default Node.js metrics (event loop, heap, GC)
-client.collectDefaultMetrics();
+// Guard all metric registration — Vite's dev server can re-evaluate
+// this module, causing "already registered" errors.
+function getOrCreate<T>(name: string, create: () => T): T {
+  return (client.register.getSingleMetric(name) as T) ?? create();
+}
 
-export const httpRequestDuration = new client.Histogram({
-  name: "http_request_duration_seconds",
-  help: "Duration of HTTP requests in seconds",
-  labelNames: ["method", "route", "status"] as const,
-  buckets: [0.01, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5],
-});
+if (!client.register.getSingleMetric("process_cpu_user_seconds_total")) {
+  client.collectDefaultMetrics();
+}
 
-export const plannerActiveSessions = new client.Gauge({
-  name: "planner_active_sessions",
-  help: "Number of active planner sessions",
-});
+export const httpRequestDuration = getOrCreate("http_request_duration_seconds", () =>
+  new client.Histogram({
+    name: "http_request_duration_seconds",
+    help: "Duration of HTTP requests in seconds",
+    labelNames: ["method", "route", "status"] as const,
+    buckets: [0.01, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5],
+  }),
+);
 
-export const plannerConnectedClients = new client.Gauge({
-  name: "planner_connected_clients",
-  help: "Number of connected WebSocket clients",
-});
+export const plannerActiveSessions = getOrCreate("planner_active_sessions", () =>
+  new client.Gauge({
+    name: "planner_active_sessions",
+    help: "Number of active planner sessions",
+  }),
+);
 
-export const brouterRequestDuration = new client.Histogram({
-  name: "brouter_request_duration_seconds",
-  help: "Duration of BRouter API requests in seconds",
-  buckets: [0.1, 0.25, 0.5, 1, 2, 5, 10],
-});
+export const plannerConnectedClients = getOrCreate("planner_connected_clients", () =>
+  new client.Gauge({
+    name: "planner_connected_clients",
+    help: "Number of connected WebSocket clients",
+  }),
+);
+
+export const brouterRequestDuration = getOrCreate("brouter_request_duration_seconds", () =>
+  new client.Histogram({
+    name: "brouter_request_duration_seconds",
+    help: "Duration of BRouter API requests in seconds",
+    buckets: [0.1, 0.25, 0.5, 1, 2, 5, 10],
+  }),
+);
 
 export const registry = client.register;
diff --git a/apps/planner/app/lib/yjs-server.ts b/apps/planner/app/lib/yjs-server.ts
index ccb22ba..af9e53f 100644
--- a/apps/planner/app/lib/yjs-server.ts
+++ b/apps/planner/app/lib/yjs-server.ts
@@ -6,6 +6,7 @@ import * as encoding from "lib0/encoding";
 import * as decoding from "lib0/decoding";
 import type { IncomingMessage, Server } from "node:http";
 import { saveSessionState, loadSessionState, touchSession } from "./sessions.ts";
+import { plannerActiveSessions, plannerConnectedClients } from "./metrics.server.ts";
 
 const messageSync = 0;
 const messageAwareness = 1;
@@ -159,10 +160,13 @@ export function setupYjsWebSocket(server: Server): WebSocketServer {
   });
 
   wss.on("connection", async (ws: WebSocket, _request: IncomingMessage, sessionId: string) => {
+    const isNewSession = !docs.has(sessionId);
     const doc = await getOrLoadDoc(sessionId);
     const awareness = getAwareness(sessionId, doc);
 
     conns.set(ws, { sessionId, clientIds: new Set() });
+    plannerConnectedClients.inc();
+    if (isNewSession) plannerActiveSessions.inc();
 
     // Broadcast doc updates to all connections in this session
     const onUpdate = (update: Uint8Array, origin: unknown) => {
@@ -218,11 +222,13 @@ export function setupYjsWebSocket(server: Server): WebSocketServer {
         );
       }
       conns.delete(ws);
+      plannerConnectedClients.dec();
       doc.off("update", onUpdate);
 
       // Save when last client leaves
       const hasClients = Array.from(conns.values()).some((m) => m.sessionId === sessionId);
       if (!hasClients) {
+        plannerActiveSessions.dec();
         saveSessionState(sessionId).catch(() => {});
       }
     });