Gyeongseok Kang, Handy
Building tools that make things handy.
Senior Software Engineer · Coupang Play, Monetization
I build payment and subscription experiences across web, app, and backend.
As a Senior Software Engineer at Coupang Play, I own payment flows and monetization on the Monetization team.
I'm strong at maintaining legacy projects and improving them step by step. I also have experience leading teams and collaborating across groups.
Beyond web and apps, I'm expanding into backend, infrastructure, and APIs—and using AI to actively solve problems for myself and my team.
As an IC, I focus on building services that create positive impact for my team and organization.
Handy's Dev Blog
+8 Years Software Engineer
397 workdays in Coupang Play
TS · JS · React · Next · Flutter · Dart
Supabase · Docker · AWS · ArgoCD · GraphQL
Git · GitHub · Jest · Cypress · CircleCI
Web Audio API · AudioWorklet · WASM · Wavesurfer.js
- 1
Seeking convenience and removing inconvenience
- 2
When it repeats, automate it.
- 3
I am responsible for every change.
Career
I make products that reduce inconvenience and find convenience.
2025.10 - current
Coupang Play
Sr.Frontend EngineerMonetization team — payment, subscription, and monetization on web and app
2020.02 - 2022.06
Tmax Tibero
Research EngineerHyperData — recommendation, analytics, and data visualization
Project
I create projects using new and good old technologies.
Local-first desktop writing app. Notes are plain Markdown that work with Obsidian and git, with wikilinks, a graph view, and AI proofreading/drafting.
Solo project · In progress
Mobile app that auto-clips swings from long golf practice videos and draws the ball flight like a shot tracer. All analysis runs on-device.
Next.js + shadcn/ui based multilingual portfolio site.
Platform connecting organizations with on-site workshop providers.
Web migration of MS Access based system + Reservation site support
Golf lesson service and membership management platform.
Financial engineering model + AI to create the best portfolio creation and recommendation
Activity
Open source, publication and lectures
- Research on Anomaly Detection using GAN model and DNN model| Graduation thesis
- 리액트, Next.js로 완성하는 프론트엔드| Book publication · 2026 Sejong Book (Academic)2026 Sejong Book
Achievements
Awards & Certifications
- 2026 세종도서 학술부문-선정도서ㄴ 『리액트, Next.js로 완성하는 프론트엔드』(영진닷컴) — 한국출판문화산업진흥원 선정
- 가우디오랩-PIETTIC 중 Integrity 수상ㄴ 신뢰도 높은 협업, 높은 수준의 업무수행으로 인한 수상
- 티맥스 표창장-우수사원상ㄴ 시각화·통계 플랫폼 관련 공로
- 우리은행 온택트 공모전-우수상ㄴ DR.폴리오: 금융공학 모델 + AI 기반 포트폴리오 생성·추천
- 청년 스타트업 어워즈, 경기도 대학생 융합 창업지원 공모전, 흑석캠퍼스타운 창업경진대회, 스마트시티즌 챌린지 외-대상, S등급, 대상, 최우수상 외ㄴ 카찹: 통합 모빌리티 플랫폼
- 한국통신학회 추계종합학술발표회-우수논문상ㄴ [UC-LAB] GAN + DNN 기반 Anomaly Detection 연구
Experience
Quarterly experiences organized as a timeline. (since 2022)
2026
3QThe book was selected as a Sejong BookCompleting Frontend with React and Next.js was selected for the 2026 Sejong Book Academic category. It will go out to public libraries, so the book starts walking on its own.- Selected by the Publication Industry Promotion Agency of Korea (KPIPA)
2QAI creates, and I raise quality by cuttingAs AI enters the workflow, I keep asking how to ship better code and design—and start with what I can do now.- Building automation skills that agents can run repeatedly.
- Reading Refactoring and Clean Code, and capturing personal code rules in an LLM wiki.
- Preparing for a platform-wide monorepo migration.
1QRaised work density with tooling and shared modulesRefined the dev flow with Claude Code and Cursor, and automated prep work with MCPs.- Cut review and onboarding busywork with Claude Code, Cursor, and MCPs.
- Started English study and aligned work with PM and ops.
- Built and shipped shared modules reused across Coupang Play products.
2025
4QJoined Coupang Play and started fresh as a seniorFocused on adapting to English work and earning trust in the team process.- Started onboarding as a Senior Engineer.
- Adapted to English meetings, docs, and code reviews.
- Learned the codebase and processes while building trust.
3QTried building an API Developer siteCleared legacy and developed user/admin tools providing APIs- Experienced documentation system from basics to deployment using Docusaurus
- Completed the first design system and applied it to a real project
- Completed a job change and wrapped up tasks
2QFocused on monorepo and design systemIntroduced a monorepo for repository management and applied it to the design system- Started managing internal packages with AWS CodeArtifact.
- Began managing a monorepo via PNPM Workspaces.
- Prepared a design system and progressed projects in parallel.
1QFocused on writing and prepared to learn new techFinished manuscript revision and began learning Elixir in earnest- Absorbing Elixir through seminars and Exercism.
2024
4QAs a lead, organized processes.Built rational processes and put effort into automating repetitive tasks- Conducted internal projects based on a browser-based media editor in development
- Established code review processes and striving to enforce them.
- Doing my best to be a good mentor
3QFinding a path between schedule and people managementLearning lead responsibilities from my lead and working to become a good lead- Developing a browser-based media editor (open source)
- Building backend knowledge using Supabase, etc.
- Striving to become a good mentor or lead
2QTook frontend lead, moving towards senior developerWorking on people and schedule management, seeking specialization- Writing tests, doing code reviews, and running a study.
- Exploring the path to become a web audio expert.
- Challenging various side projects.
1QNon-technical prep to become a better developerStarted code reviews, studied to be a good mentor, and prepared for book publication- Introduced code reviews with a junior colleague and applied automation via Bitbucket.
- Studying to become a good mentor developer.
- Received a book publication offer and started preparing.
2023
4QAdded proficiency in existing tech rather than new onesFocused on organizing the stack and deepening understanding of existing tech.- Deepened understanding of React and Next, and refactored existing projects.
- Maintaining a Flutter project to improve stability.
3QGained confidence in audio domain development.Completed internalization of the core library (Waveform-playlist) and became an open-source contributor (wavesurfer).- Completed internalization of Waveform-playlist and proceeding with added features and advancements.
- Became an open-source contributor to Wavesurfer.
- Launched a service with Flutter and improving it based on user feedback.
2QTried many fire-starting attempts to survive the winter.A very busy quarter from planning to implementation and launch- Launched Gaudio Studio-pro. A service I built started earning money.
- Picked up Flutter again for a side project.
1QEntered wintering, challenged to survive with technologyStarted developing a core library (Web Audio) and handled large files in the browser.- Improved Waveform-playlist library (TS/React support, large file optimization)
- Implemented automated data collection tools for AI models (using Puppeteer) - collected 100GB
- Launched a project with ChakraUI, Framer Motion, and TailwindCSS
2022
4QStarted laying the groundwork for various services at Gaudio LabImplemented various services and demo sites based on trust.- Performed optimizations for audio and large data.
- Made structure changes and responsive support for the existing website for mobile.
3QWorked to become a trustworthy colleague after changing jobsMigrated existing projects and learned the tech stack; a critical time to earn trust- Completed migration from class components to function components
- Introduced Next and improved data fetching with React Query
2QPrepared to change jobs and wrapped up projectsUpdated portfolio, went to interviews, finished current work and focused on documentation.- Moved from Tmax to Gaudio Lab
- Wrapped up handover and organized work
1QDecided to change jobs and tried modern stacks like Next.js and RecoilTried to step out of the old stack and explore various libraries and frameworks.- Started a side project to learn modern tech (Next.js)
- Prepared for job change, updated portfolio, and prepared for interviews