refresh.cv - Drove zero-to-one across product, architecture, full-stack engineering, UX design, data analytics, and GTM/sales - Shipped resume editor with agent-based resume authoring, revision, and feedback - Launched resume scoring and feedback based job description - Delivered resume web templates and resume card components

Toss Ads - Built and operated ad platform used in 15M+ MAU Toss app for campaign execution, review, and performance - Implemented ad performance ingestion/aggregation (impressions, clicks, plays) with Kafka, Druid, Impala - Implemented real-time CPM/CPC billing; ensured data integrity at scale with local cache + flush pattern - Contributed to settlements, agency commission payouts, and tax invoice issuance - Shipped ad account/group systems and integrated with Toss Business Display Ads product (monthly 10B+ KRW scale) - Contributed to eCPM-based ad recommendation and ranking improvements, driving >1B KRW monthly uplift - Implemented multiple optimization strategies to minimize ad refresh and serving latency, improving both UX and fill rate. - Implemented CPC (cost-per-click) and CPM (cost-per-mille) billing logic end-to-end for our ad serving pipeline. - Built real-time dashboards and alerting to monitor impressions, clicks, and spend in production, catching ad-serving incidents before they impact revenue Live Shopping - Optimized performance with tens of thousands of peak RPS without degrading UX using Local Cache, Redis and Kafka optimizations - Authored article on handling large-scale traffic without adding servers (https://toss.tech/article/monitoring-traffic) Credit Score Board - Built product aligned to financial context and user comprehension Benefits Tab (8M+ DAU) - Shipped Lucky Quiz, Lucky Lottery, Money Alerts, and Weekly Missions - Owned product development and operations from advertiser and user perspectives

founding team; leading product roadmap and led a 10-engineer team Evoclass: real-time video conference platform - Implemented WebRTC SFU with Mediasoup and high-performance socket servers using uWebSockets - Built server orchestrator and demand forecasting to reduce streaming cost and ensure efficiency - Created container-based load testing to guarantee real-time video/audio QoS and performance - Delivered real-time STT and translation via browser-native APIs - Built AI-powered video effects: background blur, virtual background, face morphing Learning Management System - Designed and implemented system architecture - Integrated with the video platform to enable AI-driven learning features