Code tab
Inspect and work with custom code screens when you need more control.
When to use it
Most users stay in Preview + Build. Use Code when you have Custom Code / advanced pages and want to review or tweak HTML/CSS/JS with the agent’s help or carefully by hand.
Client env in custom screens
Publishable keys you mark as client-side appear on window.APPIFY_ENV. Never put secrets there — see API keys & env.