diff --git a/frontend/src/app/main/data/event.cljs b/frontend/src/app/main/data/event.cljs
index d3b1555e6c..41daafdda6 100644
--- a/frontend/src/app/main/data/event.cljs
+++ b/frontend/src/app/main/data/event.cljs
@@ -61,6 +61,11 @@
 ;; Def micro-benchmark iterations
 (def micro-benchmark-iterations 1e6)
 
+;; Performance logs
+(defonce ^:private longtask-observer* (atom nil))
+(defonce ^:private stall-timer* (atom nil))
+(defonce ^:private current-op* (atom nil))
+
 ;; --- CONTEXT
 
 (defn- collect-context
@@ -464,3 +469,72 @@
 (defn event
   [props]
   (ptk/data-event ::event props))
+
+;; --- DEVTOOLS PERF LOGGING
+
+(defn install-long-task-observer! []
+  (when (and (some? (.-PerformanceObserver js/window)) (nil? @longtask-observer*))
+    (let [observer (js/PerformanceObserver.
+                    (fn [list _]
+                      (doseq [entry (.getEntries list)]
+                        (let [dur (.-duration entry)
+                              start (.-startTime entry)
+                              attrib (.-attribution entry)
+                              attrib-count (when attrib (.-length attrib))
+                              first-attrib (when (and attrib-count (> attrib-count 0)) (aget attrib 0))
+                              attrib-name (when first-attrib (.-name first-attrib))
+                              attrib-ctype (when first-attrib (.-containerType first-attrib))
+                              attrib-cid (when first-attrib (.-containerId first-attrib))
+                              attrib-csrc (when first-attrib (.-containerSrc first-attrib))]
+
+                          (.warn js/console (str "[perf] long task " (Math/round dur) "ms at " (Math/round start) "ms"
+                                                 (when first-attrib
+                                                   (str " attrib:name=" attrib-name
+                                                        " ctype=" attrib-ctype
+                                                        " cid=" attrib-cid
+                                                        " csrc=" attrib-csrc))))))))]
+      (.observe observer #js{:entryTypes #js["longtask"]})
+      (reset! longtask-observer* observer))))
+
+(defn start-event-loop-stall-logger!
+  "Log event loop stalls by measuring setInterval drift.
+  interval-ms: base interval
+  threshold-ms: drift over which we report"
+  [interval-ms threshold-ms]
+  (when (nil? @stall-timer*)
+    (let [last (atom (.now js/performance))
+          id (js/setInterval
+              (fn []
+                (let [now (.now js/performance)
+                      expected (+ @last interval-ms)
+                      drift (- now expected)
+                      current-op @current-op*
+                      measures (.getEntriesByType js/performance "measure")
+                      mlen (.-length measures)
+                      last-measure (when (> mlen 0) (aget measures (dec mlen)))
+                      meas-name (when last-measure (.-name last-measure))
+                      meas-detail (when last-measure (.-detail last-measure))
+                      meas-count (when meas-detail (unchecked-get meas-detail "count"))]
+                  (reset! last now)
+                  (when (> drift threshold-ms)
+                    (.warn js/console
+                           (str "[perf] event loop stall: " (Math/round drift) "ms"
+                                (when current-op (str " op=" current-op))
+                                (when meas-name (str " last=" meas-name))
+                                (when meas-count (str " count=" meas-count)))))))
+              interval-ms)]
+      (reset! stall-timer* id))))
+
+(defn init!
+  "Install perf observers in dev builds. Safe to call multiple times."
+  []
+  (when ^boolean js/goog.DEBUG
+    (install-long-task-observer!)
+    (start-event-loop-stall-logger! 50 100)
+    ;; Expose simple API on window for manual control in devtools
+    (let [api #js {:reset (fn []
+                            (try
+                              (.clearMarks js/performance)
+                              (.clearMeasures js/performance)
+                              (catch :default _ nil)))}]
+      (aset js/window "PenpotPerf" api))))
diff --git a/frontend/src/app/main/data/workspace.cljs b/frontend/src/app/main/data/workspace.cljs
index 6e71bcf2a6..4d71f1ec46 100644
--- a/frontend/src/app/main/data/workspace.cljs
+++ b/frontend/src/app/main/data/workspace.cljs
@@ -347,6 +347,12 @@
                                  (with-meta {:team-id team-id
                                              :file-id file-id}))))))
 
+              ;; Install dev perf observers once the workspace is ready
+              (->> stream
+                   (rx/filter (ptk/type? ::workspace-initialized))
+                   (rx/take 1)
+                   (rx/map (fn [_] (ev/init!))))
+
               (->> stream
                    (rx/filter (ptk/type? ::dps/persistence-notification))
                    (rx/take 1)