diff --git a/src/app/app.component.ts b/src/app/app.component.ts
index 73aa083..05f9406 100644
--- a/src/app/app.component.ts
+++ b/src/app/app.component.ts
@@ -1,4 +1,4 @@
-import { Component, OnInit, ElementRef, ViewChild, HostBinding, AfterViewInit } from '@angular/core';
+import { Component, OnInit, ElementRef, ViewChild, HostBinding, AfterViewInit, ApplicationRef, NgZone } from '@angular/core';
 import {MatDialogRef} from '@angular/material/dialog';
 import {PostsService} from './posts.services';
 import { MatDialog } from '@angular/material/dialog';
@@ -14,6 +14,7 @@ import { UserProfileDialogComponent } from './dialogs/user-profile-dialog/user-p
 import { SetDefaultAdminDialogComponent } from './dialogs/set-default-admin-dialog/set-default-admin-dialog.component';
 import { NotificationsComponent } from './components/notifications/notifications.component';
 import { ArchiveViewerComponent } from './components/archive-viewer/archive-viewer.component';
+import { diagCount, diagEvent, getYdmDiag } from './diagnostics';
 
 @Component({
     selector: 'app-root',
@@ -47,7 +48,10 @@ export class AppComponent implements OnInit, AfterViewInit {
   notification_count = 0;
 
   constructor(public postsService: PostsService, public snackBar: MatSnackBar, private dialog: MatDialog,
-    public router: Router, public overlayContainer: OverlayContainer, private elementRef: ElementRef) {
+    public router: Router, public overlayContainer: OverlayContainer, private elementRef: ElementRef,
+    private appRef: ApplicationRef, private ngZone: NgZone) {
+
+    this.installDiagnosticsProbe();
 
     this.navigator = localStorage.getItem('player_navigator');
     // runs on navigate, captures the route that navigated to the player (if needed)
@@ -69,6 +73,36 @@ export class AppComponent implements OnInit, AfterViewInit {
 
   }
 
+  private installDiagnosticsProbe(): void {
+    const diag = getYdmDiag();
+    diag.flags['probeInstalled'] = true;
+
+    const appRefAny = this.appRef as any;
+    if (!appRefAny.__ydmTickPatched) {
+      const originalTick = this.appRef.tick.bind(this.appRef);
+      appRefAny.__ydmTickPatched = true;
+      this.appRef.tick = (() => {
+        diagCount('appRef.tick');
+        return originalTick();
+      }) as typeof this.appRef.tick;
+      diagEvent('probe.appRef.tick.patched');
+    }
+
+    if (diag.flags['zoneSubscriptionsInstalled']) {
+      return;
+    }
+
+    diag.flags['zoneSubscriptionsInstalled'] = true;
+    this.ngZone.onUnstable.subscribe(() => diagCount('ngZone.onUnstable'));
+    this.ngZone.onMicrotaskEmpty.subscribe(() => diagCount('ngZone.onMicrotaskEmpty'));
+    this.ngZone.onStable.subscribe(() => diagCount('ngZone.onStable'));
+    this.ngZone.onError.subscribe(err => {
+      diagCount('ngZone.onError');
+      diagEvent('ngZone.onError', { message: err?.message ?? String(err) }, true);
+    });
+    diagEvent('probe.zone.subscriptions.installed');
+  }
+
   ngOnInit(): void {
     if (localStorage.getItem('theme')) {
       this.setTheme(localStorage.getItem('theme'));
diff --git a/src/app/diagnostics.ts b/src/app/diagnostics.ts
new file mode 100644
index 0000000..f710706
--- /dev/null
+++ b/src/app/diagnostics.ts
@@ -0,0 +1,96 @@
+import { NgZone } from '@angular/core';
+
+type DiagEvent = {
+  ts: string;
+  name: string;
+  inZone: boolean;
+  data?: unknown;
+};
+
+type DiagState = {
+  createdAt: string;
+  counters: Record<string, number>;
+  events: DiagEvent[];
+  flags: Record<string, boolean>;
+  lastHttp?: {
+    kind: string;
+    method?: string;
+    url?: string;
+    inZone: boolean;
+    ts: string;
+  };
+  print: () => unknown;
+  clear: () => void;
+};
+
+const MAX_EVENTS = 200;
+
+function newDiagState(): DiagState {
+  const state: DiagState = {
+    createdAt: new Date().toISOString(),
+    counters: {},
+    events: [],
+    flags: {},
+    print: () => ({
+      createdAt: state.createdAt,
+      counters: { ...state.counters },
+      lastHttp: state.lastHttp,
+      recentEvents: state.events.slice(-20)
+    }),
+    clear: () => {
+      state.counters = {};
+      state.events = [];
+      state.lastHttp = undefined;
+    }
+  };
+
+  return state;
+}
+
+export function getYdmDiag(): DiagState {
+  const g = globalThis as any;
+  if (!g.__ydmDiag) {
+    g.__ydmDiag = newDiagState();
+  }
+  return g.__ydmDiag as DiagState;
+}
+
+export function diagCount(name: string, amount = 1): number {
+  const diag = getYdmDiag();
+  diag.counters[name] = (diag.counters[name] ?? 0) + amount;
+  return diag.counters[name];
+}
+
+export function diagEvent(name: string, data?: unknown, printToConsole = false): void {
+  const diag = getYdmDiag();
+  const entry: DiagEvent = {
+    ts: new Date().toISOString(),
+    name,
+    inZone: NgZone.isInAngularZone(),
+    data
+  };
+  diag.events.push(entry);
+  if (diag.events.length > MAX_EVENTS) {
+    diag.events.splice(0, diag.events.length - MAX_EVENTS);
+  }
+
+  if (printToConsole) {
+    console.log('[YDM-DIAG]', entry.name, entry);
+  }
+}
+
+export function diagHttpCallback(kind: 'next' | 'error' | 'complete', method?: string, url?: string): void {
+  const inZone = NgZone.isInAngularZone();
+  diagCount(`http.${kind}`);
+  diagCount(`http.inZone.${inZone ? 'true' : 'false'}`);
+
+  const diag = getYdmDiag();
+  diag.lastHttp = {
+    kind,
+    method,
+    url,
+    inZone,
+    ts: new Date().toISOString()
+  };
+}
+
diff --git a/src/app/http.interceptor.ts b/src/app/http.interceptor.ts
index 88b086c..dd12982 100644
--- a/src/app/http.interceptor.ts
+++ b/src/app/http.interceptor.ts
@@ -3,13 +3,19 @@ import { inject } from '@angular/core';
 import { MatSnackBar } from '@angular/material/snack-bar';
 import { Router } from '@angular/router';
 import { throwError } from 'rxjs';
-import { catchError } from 'rxjs/operators';
+import { catchError, tap } from 'rxjs/operators';
+import { diagEvent, diagHttpCallback } from './diagnostics';
 
 export const h401InterceptorFn: HttpInterceptorFn = (request, next) => {
     const router = inject(Router);
     const snackBar = inject(MatSnackBar);
 
     return next(request).pipe(
+        tap({
+            next: () => diagHttpCallback('next', request.method, request.urlWithParams),
+            error: () => diagHttpCallback('error', request.method, request.urlWithParams),
+            complete: () => diagHttpCallback('complete', request.method, request.urlWithParams)
+        }),
         catchError((err: HttpErrorResponse) => {
             if (err.status === 401) {
                 localStorage.setItem('jwt_token', null);
@@ -20,6 +26,12 @@ export const h401InterceptorFn: HttpInterceptorFn = (request, next) => {
                 }
             }
 
+            diagEvent('http.401Interceptor.catchError', {
+                method: request.method,
+                url: request.urlWithParams,
+                status: err.status
+            });
+
             const error = err?.error?.message || err?.statusText || 'Request failed';
             return throwError(error);
         })
diff --git a/src/app/player/player.component.ts b/src/app/player/player.component.ts
index 76d4176..df44a06 100644
--- a/src/app/player/player.component.ts
+++ b/src/app/player/player.component.ts
@@ -10,6 +10,7 @@ import { TwitchChatComponent } from 'app/components/twitch-chat/twitch-chat.comp
 import { VideoInfoDialogComponent } from 'app/dialogs/video-info-dialog/video-info-dialog.component';
 import { saveAs } from 'file-saver';
 import { filter, take } from 'rxjs/operators';
+import { diagEvent } from 'app/diagnostics';
 
 export interface IMedia {
   title: string;
@@ -153,7 +154,15 @@ export class PlayerComponent implements OnInit, AfterViewInit, OnDestroy {
       this.uids = [this.db_file['uid']];
       this.type = this.db_file['isAudio'] ? 'audio' as FileType : 'video' as FileType;
       this.parseFileNames();
+      diagEvent('player.getFile.success', {
+        uid: this.uid,
+        fileUid: this.db_file?.uid,
+        show_player: this.show_player,
+        playlistLength: this.playlist?.length ?? 0,
+        currentSrcSet: !!this.currentItem?.src
+      }, true);
     }, err => {
+      diagEvent('player.getFile.error', { uid: this.uid, err: String(err) }, true);
       console.error(err);
       this.postsService.openSnackBar($localize`Failed to get file information from the server.`, 'Dismiss');
     });
diff --git a/src/app/settings/settings.component.ts b/src/app/settings/settings.component.ts
index fd9ab0c..42fccb4 100644
--- a/src/app/settings/settings.component.ts
+++ b/src/app/settings/settings.component.ts
@@ -15,6 +15,7 @@ import { ActivatedRoute, Router } from '@angular/router';
 import { Category, DBInfoResponse } from 'api-types';
 import { GenerateRssUrlComponent } from 'app/dialogs/generate-rss-url/generate-rss-url.component';
 import { filter, take } from 'rxjs/operators';
+import { diagEvent } from 'app/diagnostics';
 
 type CookiesTestResponse = {
   success: boolean;
@@ -112,8 +113,13 @@ export class SettingsComponent implements OnInit {
         // sets new config as old config
         this.initial_config = JSON.parse(JSON.stringify(this.new_config));
         this.postsService.reload_config.next(true);
+        diagEvent('settings.save.success', {
+          settingsSame: this.settingsSame(),
+          multiUserMode: this.new_config?.Advanced?.multi_user_mode
+        }, true);
       }
     }, () => {
+      diagEvent('settings.save.error', {}, true);
       console.error('Failed to save config!');
     })
   }
diff --git a/src/main.ts b/src/main.ts
index cabf9e8..c79f956 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -6,11 +6,14 @@ import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
 import { environment } from './environments/environment';
 
 import { loadTranslations } from '@angular/localize';
+import { getYdmDiag } from './app/diagnostics';
 
 if (environment.production) {
   enableProdMode();
 }
 
+getYdmDiag();
+
 const locale = localStorage.getItem('locale');
 if (!locale) {
   localStorage.setItem('locale', 'en');