diff --git a/src/app/chat/hooks/__tests__/use-chat-keyboard-diagnostics.test.tsx b/src/app/chat/hooks/__tests__/use-chat-keyboard-diagnostics.test.tsx
new file mode 100644
index 00000000..388ca2fe
--- /dev/null
+++ b/src/app/chat/hooks/__tests__/use-chat-keyboard-diagnostics.test.tsx
@@ -0,0 +1,119 @@
+/* @vitest-environment jsdom */
+
+import { type RefObject } from "react";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import {
+  installChatKeyboardDiagnostics,
+  isChatKeyboardDiagnosticsEnabled,
+} from "../use-chat-keyboard-diagnostics";
+
+vi.mock("@/utils/browser-detect", () => ({
+  BrowserDetector: {
+    getBrowserInfo: vi.fn(() => ({
+      name: "Chrome WebView",
+      version: "126.0.0.0",
+      inAppBrowserName: "facebook",
+    })),
+  },
+}));
+
+vi.mock("@/utils/platform-detect", () => ({
+  PlatformDetector: {
+    getPlatformInfo: vi.fn(() => ({
+      platform: "android",
+      osName: "Android",
+      osVersion: "15",
+      deviceVendor: "OnePlus",
+      deviceModel: "PLB110",
+    })),
+  },
+}));
+
+class MockVisualViewport extends EventTarget {
+  height = 460;
+  offsetLeft = 0;
+  offsetTop = 0;
+  scale = 1;
+  width = 390;
+}
+
+class MockVirtualKeyboard extends EventTarget {
+  boundingRect = {
+    x: 0,
+    y: 460,
+    width: 390,
+    height: 300,
+  };
+}
+
+describe("chat keyboard diagnostics", () => {
+  let consoleInfo: ReturnType<typeof vi.spyOn>;
+  let visualViewport: MockVisualViewport;
+  let virtualKeyboard: MockVirtualKeyboard;
+
+  beforeEach(() => {
+    visualViewport = new MockVisualViewport();
+    virtualKeyboard = new MockVirtualKeyboard();
+    Object.defineProperty(window, "visualViewport", {
+      configurable: true,
+      value: visualViewport,
+    });
+    Object.defineProperty(navigator, "virtualKeyboard", {
+      configurable: true,
+      value: virtualKeyboard,
+    });
+    consoleInfo = vi.spyOn(window.console, "info").mockImplementation(() => {});
+  });
+
+  afterEach(() => {
+    window.__keyboardDebugCleanup?.();
+    vi.restoreAllMocks();
+  });
+
+  it("enables diagnostics only for the explicit query parameter", () => {
+    expect(isChatKeyboardDiagnosticsEnabled("?keyboard_debug=1")).toBe(true);
+    expect(isChatKeyboardDiagnosticsEnabled("?keyboard_debug=0")).toBe(false);
+    expect(isChatKeyboardDiagnosticsEnabled("")).toBe(false);
+  });
+
+  it("records viewport events and exposes manual snapshot helpers", () => {
+    const input = document.createElement("textarea");
+    input.style.setProperty("--chat-input-lift", "314px");
+    document.body.append(input);
+    input.focus();
+    const inputRef = { current: input } as RefObject<HTMLElement | null>;
+
+    const cleanup = installChatKeyboardDiagnostics(inputRef);
+
+    expect(window.__keyboardDebugSnapshot).toBeTypeOf("function");
+    expect(window.__keyboardDebugCleanup).toBe(cleanup);
+    expect(window.__keyboardDebugSnapshot?.()).toMatchObject({
+      event: "manual",
+      visualViewportSupported: true,
+      visualHeight: 460,
+      virtualKeyboardSupported: true,
+      virtualKeyboardRect: { height: 300 },
+      activeElement: "TEXTAREA",
+      activeFocused: true,
+      inputLift: "314px",
+      platform: { name: "android", deviceModel: "PLB110" },
+      browser: { inAppBrowserName: "facebook" },
+    });
+
+    visualViewport.dispatchEvent(new Event("resize"));
+    expect(consoleInfo).toHaveBeenLastCalledWith(
+      "[keyboard-debug]",
+      expect.objectContaining({ event: "visualViewport.resize" }),
+    );
+
+    const callCount = consoleInfo.mock.calls.length;
+    cleanup();
+    visualViewport.dispatchEvent(new Event("resize"));
+    expect(consoleInfo).toHaveBeenCalledTimes(callCount + 1);
+    expect(window.__keyboardDebugSnapshot).toBeUndefined();
+    expect(window.__keyboardDebugCleanup).toBeUndefined();
+
+    input.remove();
+  });
+});
diff --git a/src/app/chat/hooks/use-chat-keyboard-avoidance.ts b/src/app/chat/hooks/use-chat-keyboard-avoidance.ts
index 7e0cbb62..466f96cf 100644
--- a/src/app/chat/hooks/use-chat-keyboard-avoidance.ts
+++ b/src/app/chat/hooks/use-chat-keyboard-avoidance.ts
@@ -13,6 +13,7 @@ import {
   type ChatKeyboardViewportBaseline,
   type ChatKeyboardViewportSnapshot,
 } from "./chat-keyboard-geometry";
+import { useChatKeyboardDiagnostics } from "./use-chat-keyboard-diagnostics";
 
 const CHAT_INPUT_LIFT_VAR = "--chat-input-lift";
 const CHAT_KEYBOARD_FALLBACK_DELAY_MS = 350;
@@ -39,6 +40,8 @@ export function useChatKeyboardAvoidance({
   const activeRef = useRef(active);
   const baselineRef = useRef<ChatKeyboardViewportBaseline | null>(null);
 
+  useChatKeyboardDiagnostics({ containerRef });
+
   useEffect(() => {
     activeRef.current = active;
   }, [active]);
diff --git a/src/app/chat/hooks/use-chat-keyboard-diagnostics.ts b/src/app/chat/hooks/use-chat-keyboard-diagnostics.ts
new file mode 100644
index 00000000..09b0bb73
--- /dev/null
+++ b/src/app/chat/hooks/use-chat-keyboard-diagnostics.ts
@@ -0,0 +1,203 @@
+"use client";
+
+import { useEffect, type RefObject } from "react";
+
+import { BrowserDetector } from "@/utils/browser-detect";
+import { PlatformDetector } from "@/utils/platform-detect";
+
+const CHAT_KEYBOARD_DEBUG_PARAM = "keyboard_debug";
+const CHAT_INPUT_LIFT_VAR = "--chat-input-lift";
+
+interface VirtualKeyboardLike extends EventTarget {
+  readonly boundingRect?: Pick<
+    DOMRectReadOnly,
+    "height" | "width" | "x" | "y"
+  >;
+}
+
+interface NavigatorWithVirtualKeyboard extends Navigator {
+  readonly virtualKeyboard?: VirtualKeyboardLike;
+}
+
+export interface ChatKeyboardDebugSnapshot {
+  event: string;
+  time: number;
+  windowInnerHeight: number;
+  documentClientHeight: number;
+  scrollY: number;
+  visualViewportSupported: boolean;
+  visualHeight: number | null;
+  visualWidth: number | null;
+  visualOffsetTop: number | null;
+  visualOffsetLeft: number | null;
+  visualScale: number | null;
+  virtualKeyboardSupported: boolean;
+  virtualKeyboardRect: {
+    x: number;
+    y: number;
+    width: number;
+    height: number;
+  } | null;
+  activeElement: string | null;
+  activeBottom: number | null;
+  activeFocused: boolean;
+  inputLift: string | null;
+  viewportMeta: string | null;
+  platform: {
+    name: string;
+    osName: string;
+    osVersion: string;
+    deviceVendor: string;
+    deviceModel: string;
+  };
+  browser: {
+    name: string;
+    version: string;
+    inAppBrowserName: string | null;
+  };
+}
+
+declare global {
+  interface Window {
+    __keyboardDebugCleanup?: () => void;
+    __keyboardDebugSnapshot?: () => ChatKeyboardDebugSnapshot;
+  }
+}
+
+export interface UseChatKeyboardDiagnosticsOptions {
+  containerRef: RefObject<HTMLElement | null>;
+}
+
+export function useChatKeyboardDiagnostics({
+  containerRef,
+}: UseChatKeyboardDiagnosticsOptions): void {
+  useEffect(() => {
+    if (!isChatKeyboardDiagnosticsEnabled(window.location.search)) return;
+    return installChatKeyboardDiagnostics(containerRef);
+  }, [containerRef]);
+}
+
+export function isChatKeyboardDiagnosticsEnabled(search: string): boolean {
+  return new URLSearchParams(search).get(CHAT_KEYBOARD_DEBUG_PARAM) === "1";
+}
+
+export function installChatKeyboardDiagnostics(
+  containerRef: RefObject<HTMLElement | null>,
+): () => void {
+  window.__keyboardDebugCleanup?.();
+
+  const removers: Array<() => void> = [];
+  let disposed = false;
+
+  const takeSnapshot = (event: string): ChatKeyboardDebugSnapshot => {
+    const snapshot = createChatKeyboardDebugSnapshot(event, containerRef);
+    window.console.info("[keyboard-debug]", snapshot);
+    return snapshot;
+  };
+
+  const listen = (
+    target: EventTarget | null | undefined,
+    eventName: string,
+    label = eventName,
+  ) => {
+    if (!target) return;
+    const handler = () => takeSnapshot(label);
+    target.addEventListener(eventName, handler);
+    removers.push(() => target.removeEventListener(eventName, handler));
+  };
+
+  const cleanup = () => {
+    if (disposed) return;
+    disposed = true;
+    removers.forEach((remove) => remove());
+    if (window.__keyboardDebugSnapshot === manualSnapshot) {
+      delete window.__keyboardDebugSnapshot;
+    }
+    if (window.__keyboardDebugCleanup === cleanup) {
+      delete window.__keyboardDebugCleanup;
+    }
+    window.console.info("[keyboard-debug] removed");
+  };
+  const manualSnapshot = () => takeSnapshot("manual");
+  const virtualKeyboard = getVirtualKeyboard();
+
+  listen(window, "resize", "window.resize");
+  listen(window, "scroll", "window.scroll");
+  listen(window, "orientationchange", "orientationchange");
+  listen(document, "focusin", "focusin");
+  listen(document, "focusout", "focusout");
+  listen(document, "visibilitychange", "visibilitychange");
+  listen(window.visualViewport, "resize", "visualViewport.resize");
+  listen(window.visualViewport, "scroll", "visualViewport.scroll");
+  listen(virtualKeyboard, "geometrychange", "virtualKeyboard.geometrychange");
+
+  window.__keyboardDebugSnapshot = manualSnapshot;
+  window.__keyboardDebugCleanup = cleanup;
+  takeSnapshot("installed");
+
+  return cleanup;
+}
+
+function createChatKeyboardDebugSnapshot(
+  event: string,
+  containerRef: RefObject<HTMLElement | null>,
+): ChatKeyboardDebugSnapshot {
+  const visualViewport = window.visualViewport;
+  const virtualKeyboardRect = getVirtualKeyboard()?.boundingRect ?? null;
+  const activeElement = document.activeElement;
+  const activeRect =
+    activeElement instanceof HTMLElement
+      ? activeElement.getBoundingClientRect()
+      : null;
+  const platform = PlatformDetector.getPlatformInfo();
+  const browser = BrowserDetector.getBrowserInfo();
+
+  return {
+    event,
+    time: Math.round(performance.now()),
+    windowInnerHeight: window.innerHeight,
+    documentClientHeight: document.documentElement.clientHeight,
+    scrollY: window.scrollY,
+    visualViewportSupported: visualViewport != null,
+    visualHeight: visualViewport?.height ?? null,
+    visualWidth: visualViewport?.width ?? null,
+    visualOffsetTop: visualViewport?.offsetTop ?? null,
+    visualOffsetLeft: visualViewport?.offsetLeft ?? null,
+    visualScale: visualViewport?.scale ?? null,
+    virtualKeyboardSupported: getVirtualKeyboard() != null,
+    virtualKeyboardRect: virtualKeyboardRect
+      ? {
+          x: virtualKeyboardRect.x,
+          y: virtualKeyboardRect.y,
+          width: virtualKeyboardRect.width,
+          height: virtualKeyboardRect.height,
+        }
+      : null,
+    activeElement: activeElement?.tagName ?? null,
+    activeBottom: activeRect?.bottom ?? null,
+    activeFocused: activeElement !== document.body,
+    inputLift:
+      containerRef.current?.style.getPropertyValue(CHAT_INPUT_LIFT_VAR) || null,
+    viewportMeta:
+      document.querySelector<HTMLMetaElement>('meta[name="viewport"]')
+        ?.content ?? null,
+    platform: {
+      name: platform.platform,
+      osName: platform.osName,
+      osVersion: platform.osVersion,
+      deviceVendor: platform.deviceVendor,
+      deviceModel: platform.deviceModel,
+    },
+    browser: {
+      name: browser.name,
+      version: browser.version,
+      inAppBrowserName: browser.inAppBrowserName,
+    },
+  };
+}
+
+function getVirtualKeyboard(): VirtualKeyboardLike | null {
+  return (
+    (navigator as NavigatorWithVirtualKeyboard).virtualKeyboard ?? null
+  );
+}