Toivo Mattila restructured the Kesäseteli development environment for the City-of-Helsinki/yjdh repository, focusing on improving local development speed and onboarding efficiency. He refactored Docker Compose configurations to separate base, employer, and handler services, introduced distinct development and production Yarn targets, and enhanced compatibility with Linux and WSL. Toivo also overhauled the project’s documentation, reorganizing the README with a comprehensive table of contents, detailed service environment descriptions, and expanded setup and troubleshooting guidance. Leveraging skills in DevOps, Docker, and technical writing, his work streamlined contributor handovers and reduced setup errors, laying a foundation for more maintainable future development.