Forms, validation, and error states

Client-side validation is a convenience; the server check is the real one. Parse the payload on arrival and return errors the form can render.

What this lesson covers

• Validate submitted data on the server before writing
• Return structured field errors back to the form
• Keep the form usable when JavaScript has not loaded

This lesson sits in Server Actions and Mutations, part of Next.js App Router in Depth. It assumes what came before it and leads directly into the next lesson in the module.