diff --git a/webui.py b/webui.py
index eef1e3c..a5d0fbb 100644
--- a/webui.py
+++ b/webui.py
@@ -171,6 +171,18 @@ async def run_custom_agent(
             playwright = await async_playwright().start()
             chrome_exe = os.getenv("CHROME_PATH", "")
             chrome_use_data = os.getenv("CHROME_USER_DATA", "")
+
+            if not chrome_exe:
+                raise ValueError("You selected use own browser, but CHROME_PATH environment variable is not set. Please set it to your Chrome executable path.")
+            
+            if not os.path.exists(chrome_exe):
+                raise ValueError(f"Chrome executable not found at {chrome_exe}")
+            if not chrome_use_data:
+                raise ValueError("You selected use own browser, but CHROME_USER_DATA environment variable is not set. Please set it to your Chrome user data directory.")
+            
+            if not os.path.exists(os.path.expanduser(chrome_use_data)):
+                raise ValueError(f"Chrome user data directory not found at {chrome_use_data}")
+            
             browser_context_ = await playwright.chromium.launch_persistent_context(
                 user_data_dir=chrome_use_data,
                 executable_path=chrome_exe,