Worked on the Hackaton-Yad-Tamar/Back repository to enhance backend data contracts supporting user authentication and manager data workflows. Focused on Python-based API design and data modeling, the work introduced three new Pydantic DTOs for user sign-in, sign-up, and manager data, each enforcing strict validation for fields like email and password hashes. Refactored the DTO architecture by centralizing schemas and leveraging inheritance to improve maintainability and code reuse. Further refinements included adding post-signup data handling, clarifying field names, and supporting volunteer-specific signup flows. The changes prioritized data integrity and contract stability, laying groundwork for scalable authentication features without introducing defects.