Joel developed and enhanced expense duplication workflows in the Expensify/App and callstack-internal/Expensify-App repositories, focusing on user experience, policy compliance, and internationalization. He implemented navigation guards and modal feedback to prevent unintended duplications and policy violations, while expanding Spanish translations and multi-language error messages to improve accessibility. Using JavaScript, TypeScript, and React, Joel strengthened error handling and stabilized code quality by addressing TypeScript errors, refining test coverage, and introducing optional chaining. He also improved observability by adding Sentry labels for modal monitoring and centralized error reporting, supporting faster debugging and maintainability. His work demonstrated depth in both front and back end development.