Form Validation Mismatch Between Client and Server

1. Client uses custom validation rules, server uses different schema (Zod, Joi)
2. Only client-side validation, no server-side validation of submitted data
3. Server action accepts data without validation before database insert
4. Different field requirements or constraints on client vs server
5. No shared validation schema between front and backend

Use shared schema: Define validation with Zod schema used on both client and server:
const schema = z.object({ email: z.string().email(), name: z.string().min(2) })
// In client component: schema.parse(data)
// In server action: schema.parse(formData)

Always validate server-side: Never trust client validation. Always validate in server action before database operation.

Return validation errors: Server action should return validation errors to display in form: return { errors: { email: 'Invalid email' } }

Use form libraries: React Hook Form + Zod handles both validation and error display.