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Hyukjun Yoon
Software engineer who uses generative AI throughout development to deliver products across backend, frontend, and infrastructure.
About Me
I am a software engineer who centers on backend engineering and connects frontend and infrastructure work as needed to turn business requirements into production-ready product capabilities. I have redesigned legacy payment and authentication domains on Java/Spring and introduced LLM diagnostic pipelines and AI-powered CS automation in production, improving service reliability and operational efficiency. I treat generative AI as a development partner, not merely a code generator. I integrate it across requirements analysis, codebase exploration, design, implementation, testing, review, and documentation, while personally validating outcomes against official documentation, executable code, automated tests, and production data.
AI-native Development
AI throughout the development lifecycle
I integrate generative AI agents into the daily development loop, from requirements analysis and codebase exploration to design, backend/frontend implementation, testing, code review, and documentation.
End-to-end product delivery
With Java/Spring as my backend foundation, I connect React/TypeScript interfaces, E2E tests, deployment, and observability to deliver complete product features.
Verifiable outcomes
I use MCP and official documentation to check current specifications, then validate AI-generated work through compilation, automated tests, runtime logs, and production metrics before adopting it.
Experience
Day1 Company
Backend Engineer
Aug 2024 - Present
- •In progress: backend and app localization for entering the Japanese market
- •Diversified authentication by adding LINE, Google, and Apple social login, and integrated a LINE friend-add prompt for Japanese users
- •Built the app internationalization (i18n) foundation with GCS runtime-loaded language packs and bundle fallback, using a GrowthBook kill switch for zero-downtime rollout
- •Cleaned up hardcoded Korean into message-based strings with locale fallback
- •Added user language and timezone (locale) settings APIs and screens, and propagated language codes to authenticated user data
- •Rebuilt issued documents (completion certificates, level-test reports) from an image-based approach to an HTML rendering architecture for multilingual support — adding a new language now means adding a string file, not redrawing per-language background images
- •The backend only publishes issuance events; rendering is delegated to a Cloud Run service that renders HTML templates and locale strings into PDF
- •Implemented language-based home banner segmentation
EXEM
Backend Engineer
Jul 2020 - May 2024
- •Reworked MyBatis queries with subquery structures to avoid query-size limits from large parameter sets
- •Combined multiple split read queries into a single query to improve response performance
- •Implemented core business logic for a database analysis tool
- •Improved large data read performance to respond within 100ms to 3s
- •Provided database status and analysis metrics visually in the user interface