Nextjs Guideline: DataFetching — Use Server Actions for mutations. Description: Server Actions for form submissions. Do: action={serverAction} in forms. Don't: API route for every mutation. Good Example: <form action={createPost}>. Bad Example: <form onSubmit={callApiRoute}>. Severity: Medium. Docs: https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions-and-mutations.