Mateus standardized input validation across the AppCivico/smae repository by introducing reusable constants for character limits within Data Transfer Objects. He replaced hardcoded values with centralized constants such as MAX_LENGTH_DEFAULT and MAX_LENGTH_MEDIO, using TypeScript and leveraging NestJS for backend development. This approach established a single source of truth for validation rules, improving maintainability and reducing the risk of inconsistencies as the codebase evolves. His work focused on refactoring and DTO validation, enabling easier future updates and minimizing validation drift. The depth of the change lies in its impact on code quality and the maintainability of input validation logic.