Mertushka contributed to the DefinitelyTyped/DefinitelyTyped repository by delivering enhancements to the Haxball Headless Browser typings. Over the course of a month, they added a new player chat event and improved admin management features, focusing on robust API development and comprehensive documentation. Using TypeScript, Mertushka refined type safety by addressing return types and missing traits, while also expanding JSDoc coverage to clarify usage for downstream developers. These updates improved the reliability and maintainability of the headless-browser integration, reducing onboarding time and runtime risk. The work demonstrated a strong grasp of TypeScript typings, API surface design, and collaborative open-source workflows.