About Me
I develop AI products on the Kanvas TF at Kakao. In 2025 I architected the internal AI search system from scratch, cutting API cost by 94% and tokens by 50%. From the second half of that year into early 2026 I designed and built the system behind AITOP100, a competition platform for AI proficiency, and earlier still, on the AI Native Company TF, I built a knowledge base with GraphRAG.
Before the AI work I spent years on large-scale service backends. I developed and operated Daum Mail for more than 8 years — over 20 million MAU and hundreds of millions of emails a day — which took me through the infrastructure, monitoring and incidents of a service already two decades old. I helped build and launch the My Subscription service from scratch, and contributed to Tistory, OpenLink and OpenChat.
I document what I learn and share it with my colleagues. I automate repetitive work with scripts and build internal tools to reduce operational cost.
Skills
AI / LLM
- LLM application development - RAG (GraphRAG), LLM integration & model routing
- Automated LLM grading pipelines, prompt injection guardrails
Back-end
- Primary: Java, Kotlin, Python, Linux, MySQL, Kafka
- Others: PostgreSQL, C, Perl, Oracle, PHP, etc.
- Frameworks: Spring, SpringBoot, FastAPI
Front-end
- Javascript, jQuery, Bootstrap, React
Others
- Git & Github, Kubernetes, Docker
- Ansible, Jenkins, ArgoCD
Experience
- Kanvas TF - 2026.05 ~ Present
- AI service development
- AI TOP 100 Builder TF - 2026.02 ~ 2026.04
- Worked on the 2026 AITOP100 Campus and AITOP100 Challenge projects
- AI Native Strategy - 2025.07 ~ 2026.01
- Built an internal AI search system - designed the architecture with no prior art to draw on. Cut tokens by 50% through context and prompt optimization, and API cost by 94% by switching models and removing unnecessary processing steps
- Launched internally in April and kept improving it until handover in August; crews have kept using it since
- Built AI Buddy and other internal tools
- Worked on the 2025 AITOP100 and AITOP100 Challenge projects
- Kadenbell at if(kakao)25 Krew Day - planned and built the mobile quiz platform for a CS/AI tech quiz session (two people)
- Sign-up, entry, gameplay and rankings all ran self-serve on each participant’s own phone; 60 concurrent players, no incidents
- Kakao Tech blog (Korean)
- Built an internal AI search system - designed the architecture with no prior art to draw on. Cut tokens by 50% through context and prompt optimization, and API cost by 94% by switching models and removing unnecessary processing steps
- AI Native Company TF - 2024.07 ~ 2025.06
- Built a knowledge base using GraphRAG
- OpenChat Development Part - 2024.04 ~ 2024.06
- OpenLink Development Part - 2023.08 ~ 2024.03
- Personalized chat room recommendations, push notification server
- Tistory Development Part - 2022.06 ~ 2023.08
- White Blog and others
- My Subscription Development Part - 2020.04 ~ 2022.06
- Developed and operated the My Subscription service - Java, SpringBoot, Kafka, MySQL, Redis, Kubernetes
- Built Web APIs in an MSA environment, Pub/Sub data processing with Kafka
- Mail Development Part - 2012.01 ~ 2020.04
- Developed and operated Daum Mail for more than 8 years - over 20 million MAU, hundreds of millions of daily send/receive transactions, with deployment, monitoring and log collection across hundreds of servers
- Modernised a 20-year-old codebase - removed over 4 million lines of unnecessary code, restructured, and upgraded Java, JUnit, the OS, httpd and Tomcat
- Large migrations - Oracle to MySQL, 32bit to 64bit OS, IDC relocation, physical to virtual machines
- Email domain knowledge - mail protocols such as SMTP and LMTP, DNS records such as MX, SPF and DKIM
- Eight years of detail →
Qualcomm CDMA Technologies Korea
Assistant Software Engineer
July 2011 ~ Dec 2011
https://www.qualcomm.com
- Supported the multimedia team. Developed build helper tools.
- C, JTAG, Android, Python
- Supported molecular modeling research. Built a tool that reads molecular data and renders 3D models.
- OpenGL, Python
- Flucard (Wifi SD Card) - built a web photo viewer and management tool running on an embedded OS
- iBall (Wifi Camera) - device driver work and hardware debugging
- Linux, JTAG, CGI, C, lighttpd
- Built the industry-academic research support system for Kyungpook National University
- Built Winitech’s project management system
- Oracle, Java, JBoss, Javascript, MiPlatform
Yeongcheon National Cemetery
Software Engineer
Mar 2005 ~ Aug 2005
https://www.mpva.go.kr/ycnc/index.do
- Built the Yeongcheon National Cemetery website
- PHP, MySQL, Flash
Projects
AITOP100 - AI Proficiency Competition Platform
2025 - 2026
- 2025 AI TOP 100 — owned the common modules: system design, infrastructure and the skeleton projects
- Analysed the load scenarios for thousands of concurrent users and designed the staged answer, including triple-IDC redundancy
- Two of us completed skeletons in Java, Python and JavaScript in a week, wired into internal storage and authentication
- Co-authored the write-up on Kakao’s tech blog - What AI TOP 100 left us (Korean)
- AITOP100 Challenge — built the submission and automated LLM grading site
- Kafka-based asynchronous grading pipeline separating submission from grading, worker pool backpressure via semaphores, at-least-once idempotent re-grading
- Multi-persona LLM grading on virtual threads with score aggregation, prompt injection guardrails
- Anti-cheating measures — one submission per problem, invalidation of duplicate submissions
- 2026 AITOP100 Campus — built and operated the competition for university and high school students
- Opened preliminary and final rounds on the Challenge site, ran LLM grading (resolved grading prompt issues collaboratively)
- 3,002 applicants (4.3x the previous year’s 700), 179 universities nationwide plus 18 overseas universities and high schools (5.6x growth in high school participants)
- Java, Kotlin, Kafka, MySQL, Kubernetes
- Joined the build of a new service, launched it, and developed and operated it for the next two years
- Designed and built Web APIs in an MSA environment, with Kafka pub/sub moving data between services
- Java, SpringBoot, Kafka, MySQL, Redis, Kubernetes
- Replaced the outbound mail server from Sendmail with a Java server, adding TLS mail delivery
- Set up the user settings server, mail receive event delivery server, mail cleanup batch, outbound mail server, log collection, statistics and operational tools. Handled signup and event draw features
- Kakao Mail project - applied cmake to the legacy C mail codebase, replaced the sendmail-based outbound server with a Java server
- C, Java, MySQL
Mail Delivery Log Collection System and Search Tool
2016
- Addressed how difficult it was to check mail delivery results
- Parsed delivery logs with Logstash and forwarded them to Kafka
- Logs flowed through Storm into HBase
- Built an API to query logs from HBase and an operational tool on top of it - NodeJS
Decoupling the Member System from the Mail System
2015
- Removed the dependency between the member system and the mail system - C
- Signup and withdrawal processing system - SpringBoot, RabbitMQ
- Group mail
- Strengthened monitoring
EMS - Bulk Mail Delivery System
2014
- Rebuilt the bulk mail delivery system
Unified Corporate Mail
2014
- Merged mail accounts from both companies after the merger
Mail - CS System Integration
2013, 2016
- Mail to customer service system integration
- 2016 rewritten from Python to Java
- 2013 rewritten from Perl to Python
Smart Work
2013
- Revamped the existing domain mail service into the Smart Work service
- Java
Paran Mail Migration
2012
- Migrated users into Daum Mail after Paran Mail shut down
Seolleneun Library
2012
- Built the in-house library system
- Spring
External Activities
Hackathons
- 2025 Kakao internal hackathon 10K - “Actually, this one’s a bit cheaper”, an agent that tracks AI API spend and recommends cheaper models (Python, Google A2A/ADK)
- Themed on agentic AI - an orchestrator directing statistics, model-recommendation and reporting agents over A2A, built to an MVP within the 10-hour format
- Article (Korean)
- 2022 Kakao internal hackathon 24K - web screen sharing tool (Node, WebRTC)
- 2019 Kakao internal hackathon 24K - 24K GOLD thumbnail creation tool (Javascript)
- 2017 Social Innovation Camp 36 - Pick Art You - won both the Completion Award and the Social Innovation Award (PHP, CodeIgniter, MySQL)
- A web service for student creators to exhibit and share work that would otherwise be discarded
- Article
- 2014 Social Innovation Camp 36 - ThumMap - Completion Award
- 2013 Social Innovation Camp Seoul - Finger Town - 1st prize
- An app that turns filing civic complaints into a game. Won the Seoul round of the 48-hour hackathon and advanced to the Singapore final
- Article - The Dong-A Ilbo, “Solving social problems with IT: hackathons light up the world” (Korean)
- 2012 Social Innovation Camp 36 - app for children in special education - Social Impact Award
Mentoring
- 2026 Kakao Tech Campus (4th cohort) mentor (Jun ~ Nov 2026)
- Stage 1 - code review mentoring, technical mentoring sessions, and support for using AI tools
- Stage 2 - team mentor, from tech spec review through development, deployment and the final presentation
- 2026 Kakao Tech for Impact 26-1 mentor (Apr ~ Jun 2026)
- Mentored a team under the Seoul Environmental Federation on Onloop, a campus platform for circulating household goods among exchange students
- Final showcase (Korean)
Communities & Talks
- 2024.10.24 if(kakao)AI 2024 crew panel talk, panelist - growing an AI career, the doubts that come with it, and applying the technology at work
- Event Stage, Team ground / 52-minute live outdoor session
- Talk details
- 2019~2022 Gardeners - a daily commit community. Participated in seasons 2~7
- Built the attendance board - season 7 board
- 2019.11.15 GDG DevFest Pangyo - spoke on building the Gardeners attendance checker (track B, Kakao Pangyo office)
- Slides · event recap video · attendee write-up with the agenda (Korean)
Education
Kyungpook National University
B.S. in Computer Science, College of IT Engineering
2004 - 2012
- Software development club (Haneulso) - club president in 2005
- 2011 LED sheet music composer & player - Grand Prize (C)
- 2010 Acupuncture point learning app - Silver Prize (Android) / English vocabulary app - Silver Prize (Android, QRCode) demo / Balancing Lego robot (Android, Bluetooth)
- 2009 Shopping assistant - Silver Prize (Android, QRCode)
- 2005 Rhythm game (WinAPI, DirectX, MIDI), club website (PHP, MySQL)
- 2004 Photo Story image editor - Special Prize (MFC)
- Projects
- 2011 Remote robot arm control with Kinect (MFC, Kinect) - drove a robot arm from Kinect gesture tracking. Demo video
- 2011 KNUSNS (PHP, MySQL, JavaScript), AR timetable (Android)