Give the agent one small page to build before asking for an entire application. Write down what should appear on the page and what should happen when someone clicks its main button. This gives you something specific to check.
Keep a copy before the next change. When the result is wrong, describe the visible problem and ask for a single correction. A page that opens is only the beginning; check its links and try the form with empty fields too.
Evgenii Arsentev covers this starting point in his guide to a first prompt that builds, part of his free Claude Code course. The guide is for beginners; it does not replace checking the code and the result yourself.