Orrery (혼천의)
Birth chart calculator for Eastern and Western astrology.
An open-source client-side astrology calculator that computes three distinct chart systems entirely in the browser with zero backend. Implements a pure TypeScript planetary ephemeris based on Moshier's analytical theory — no WASM, no external data files. Available in Korean, Chinese, Japanese, and English. Core engine published as an npm package (@orrery/core).
Key Features
- Four Pillars of Destiny (사주팔자) — Classical Chinese astrology based on the 60-year Heavenly Stem & Earthly Branch cycle. Analyzes Ten Gods, 12 life stages, hidden stems, elemental interactions (合/沖/刑/破/害), 10-year major luck periods (大運), and daily/monthly transits
- Zi Wei Dou Shu (자미두수) — Traditional Chinese star-chart system using the lunar calendar. Places 14 major stars across a 4×4 palace grid (命盤), with brightness ratings, Four Transformations (四化), and decade/annual fortune forecasting
- Natal Chart (점성학) — Full horoscope with 10 planets, Chiron, and lunar nodes across 12 houses. Supports 10 house systems (Placidus default), 5 major aspects, and an interactive SVG zodiac wheel
- AI-agent-friendly combined text export for all three chart systems
- Profile management, dark/light theme, fully responsive
Feb 2026
Feb 2026
79
React, TypeScript
Technical Details
Pure Client-Side Ephemeris
Planetary positions computed using Steve Moshier's analytical ephemeris theory implemented entirely in TypeScript, with no server calls, no WASM compilation, and no external data files.
Lunar Calendar Engine
Full solar-to-lunar calendar conversion supporting leap months, required for accurate Four Pillars and Purple Star calculations.
Interactive SVG Zodiac Wheel
The Western natal chart renders as a fully interactive SVG with zodiac ring, house cusps, aspect lines, and planet markers.
npm Package (@orrery/core)
Core calculation engine published separately for programmatic use, enabling integration into other applications.
Mouton Journal
Private diary with a cute AI companion.
A subscription-based commercial iOS app (actively developed until April 2025). I built everything from ideation to planning, design, and back-office tools entirely on my own. Available in 8 languages: English, German, Korean, Japanese, Chinese, French, Italian, and Spanish.
Key Features
- AI Companion that likes your posts and writes empathetic comments on your diary entries
- Clean, social media-inspired design
- Calendar view and search functionality
- Optimized for iPhone and iPad, also runs on macOS (Apple Silicon)
- Support for comments and quote-sharing
- PDF export
Jan 2025
Mar 2025
1,653
Flutter, Django
Technical Details
🗄️ Offline-First Architecture
All journal entries are stored locally using SQLite with FTS5 (Full-Text Search) for instant search capabilities. Data syncs to the server when online with sophisticated conflict resolution and change tracking.
🤖 AI-Powered Interactions
Mouton's personality is powered by OpenAI's GPT models with custom prompt engineering. Includes content moderation, emotion matching, and multi-language support. Comments are generated contextually based on entry content and attached images.
🦀 Rust Integration
Performance-critical operations like image resizing are handled by Rust modules viaflutter_rust_bridge. Uses the fast_image_resize crate for efficient image processing, ensuring smooth performance even with multiple high-resolution photos.
🔄 Smart Synchronization
Implements a sophisticated sync protocol with change tokens, automatic conflict resolution, and retry logic. Supports offline post creation with automatic sync when reconnected.
🔗 Rich Content Support
Automatic link preview generation with OpenGraph parsing, special YouTube handling, and support for quoting other entries or comments in a social media-style interface.
iOS Apps built in Collaboration
9 side projects created with designer Eui-Hyung Jung (2015-2023)
Sole developer on all projects (Swift, Objective-C, Flutter)
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Work Experience
Software Architect
Building and operating BizRouter, an LLM gateway for the Korean enterprise market. At its core is a high-performance Rust API proxy handling streaming responses, tool calling, multimodal inputs, and provider-agnostic routing across OpenAI, Anthropic, Google Gemini, and more — behind a single OpenAI-compatible interface. Includes GCRA-based rate limiting, token-level usage metering, BYOK encryption, and PII masking for Korean data privacy compliance (PIPA).
On top of BizRouter, shipped three customer-facing AI applications — AI Image Generation, AI Video Generation, and AI Meeting Notes — each taken from initial product planning and UX design through full-stack implementation to production deployment and ongoing operations, entirely solo.
Software Architect
Built and optimized an AI-powered coding agent with Python and TypeScript, focusing on maintenance, feature delivery, and Claude Code-driven development workflows.
Product Owner & Engineer
Architected and launched Mouton Journal for iOS, built Django-Ninja and PostgreSQL APIs, integrated LiteLLM-powered diary comments, and used Rust for performance-critical photo resizing.
Senior Software Engineer
Architected APIs and infrastructure for the Japanese e-commerce platform nugu.jp, built product and back-office systems with Next.js, TypeScript, Django, and Svelte, and mentored the team on Django practices.
Chief Technology Officer
Led company-wide API architecture with Django, React, and PostgreSQL, cut AWS infrastructure costs by 75 percent, and managed a fully remote engineering team across time zones.
Chief Technology Officer
Led development of a Flutter-based K-pop fandom app to 10K+ users, built scalable Django and PostgreSQL APIs, and engineered real-time video broadcasting with WebRTC, RTMP, FFmpeg, and CUDA.
Senior Software Engineer
Architected the chatbot engine for Kakao's smart speaker, built an Angular management console for internal teams, and ported a high-traffic KakaoTalk server from Linux to macOS for faster local development.
Chief Technology Officer
Co-founded the company, shipped a native iOS app in Swift, built a Flask and SQLAlchemy backend on AWS, and mentored two junior developers through launch.
Senior Software Engineer
Designed a UI test automation platform for Need for Speed Edge with Angular, Node.js, TypeScript, and Docker, reducing QA time by 70 percent.
Senior Software Engineer
Developed a social music player for Android and maintained a high-traffic Python API server handling more than 1 million daily requests.
Senior Software Engineer
Optimized AWS infrastructure to save about $200K per month, improved Django performance for 10M+ daily requests, and built Java-based sharding middleware for horizontal scaling.
Professional Consultant
Prototyped a Node.js comment backend, researched a CloudFoundry-based PaaS, and developed a custom Nginx extension in C and GLib for request handling.
Independent Software Engineer
Built an Android MSN Messenger clone that reached 2M+ downloads and generated more than $100K in ad revenue while handling the full product lifecycle alone.
Software Engineer
Developed SpringNote messaging integrations, implemented an OpenID-based private messaging service, and built a Firefox extension for content collection and metadata extraction.
Software Engineer / Lead Software Engineer
Worked across CyberImagination, Linux Korea, Tri-D Communication, and National Grid, building Java financial systems, RFC-based network authentication modules, Oracle-backed web services, and Java grid middleware while leading small engineering teams.