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Soojin Jung

Frontend Engineer for AI Products

sojjung3@gmail.com · linkedin.com/in/soo-jin-jung · github.com/soojjung · medium.com/@sojjung3

Summary

Frontend engineer with 3 years building React-based financial services at two fintech companies. I owned areas where mistakes aren't tolerated: payments and refunds, JWT authentication, and role-based access control. I also built a design system and introduced a PR review process that cut post-release bugs by 40%.

I built AI-facing interfaces, including an SSE streaming chatbot UI and GPT-4o Vision recommendations with model fallback. Since 2025, I completed backend/AI and physical AI bootcamps and ran my own products, reaching 85,000+ diagnoses and shipping two App Store apps.

Skills

Frontend

React TypeScript JavaScript Next.js TanStack Query Zustand Recoil Tailwind CSS SSE Streaming UI Toss Payments SDK Capacitor

AI & Backend

Python RAG Pipelines LangChain ChromaDB OpenAI API FastAPI REST APIs PostgreSQL Supabase

Tools & Operations

Sentry GitHub Actions AWS S3/CloudFront Vercel Playwright Vitest GA4 Mixpanel

Languages

English (Fluent) Korean (Native)

Work Experience (3 yrs)

Frontend Developer

BeHappy · AI financial roadmap service for newlyweds

Oct 2024 — May 2025 (8 months - service discontinued)

  • Implemented the Toss Payments SDK payment and refund flow for paid financial chatbot consultations with reports, handling edge cases such as mid-payment exits, re-entry, and back navigation.
  • Built the SSE streaming chatbot UI — token-by-token rendering with a typing delay, input locking while answers stream, and report terms that open chatbot explanations.
  • Visualized 30+ financial reports with Chart.js, covering income, debt, DSR, retirement, and more.
  • Tracked each step up to payment completion with GA4 / Mixpanel to find drop-off points and the actual user base for future planning, revealing a 60+ user segment and 95% mobile access.
  • Built an automated deployment pipeline to S3/CloudFront with GitHub Actions, deploying on PR merge and eliminating missing environment variable errors.
JavaScript React 18 Toss Payments SDK Recoil Chart.js Zod Tailwind CSS GitHub Actions GA4

Frontend Developer

aiZENGlobal · Receivables-backed loan brokerage for e-commerce sellers

Mar 2022 — Jun 2024 (2 years 4 months)

  • Architected and built a tri-portal ecosystem from the ground up for customers, internal operations, and financial partners, reaching a 34% loan application conversion rate (sign-ups to applications) on the customer portal (KB Kookmin Bank loan-matching platform).
  • Built JWT auto-renewal with a Request Queue pattern, preventing concurrent request failures and session drops on token expiry.
  • Implemented financial-grade security: secondary identity verification, auth route guards, a 5-minute lockout after 10 failed logins, and DOMPurify-based XSS protection.
  • Implemented a three-tier permission system controlling screen, menu, and button access by role, extensible through configuration alone.
  • Built a design system of 50+ reusable UI components to restore UI consistency without a designer, and cut development time by 50% across 30+ pages with a shared SearchTable module (against original schedule estimates).
  • Introduced a PR review process and code conventions as the team grew, cutting post-release bugs by 40% (JIRA issues) and refactoring time by 30% (against original schedule estimates).
JavaScript React 18 Context API Styled-components Ant Design Axios

Selected Projects

AI Wellness App for Women's Health (dwee)

dwee-neon.vercel.app · github.com/soojjung/dwee-wellness-tracker

May 2026 — Present

  • Designed a local-first architecture (Repository/Adapter) with IndexedDB offline storage and cloud migration on login.
  • Supported keyboard and screen reader accessibility with shared modal hooks, ARIA roles/states, focus-visible, and aria-live.
  • Verified cycle prediction logic as pure functions with 724 unit tests, and caught 4 refactoring regressions with Playwright visual tests.
  • Configured Claude Code with role-specific sub-agents, domain rules, and a /commit quality gate (lint → tests → docs sync → PR).
TypeScript React 19 Next.js 15 Zustand IndexedDB Supabase Vitest Playwright Sentry

Personal Color Self-Diagnosis Service

omct.web.app · github.com/soojjung/personal-color-self-diagnosis

Feb 2023 — Aug 2024 · AI feature added Jul 2026

  • Designed a 9-stage algorithm using 36 curated chips and a bonus-round re-evaluation.
  • Recorded 85,000+ diagnoses and 27,600+ annual active users (AAU) in 2025 (GA4), with a 91.5% completion rate.
  • Added GPT-4o Vision color recommendations for users unsure of their picks, balancing cost and accuracy with gpt-4o-mini → gpt-4o fallback routing.
  • Reached Google's first page for “퍼스널컬러 테스트” (personal color test) through SSR and SEO optimization, with 83% of traffic from organic search.
TypeScript React 18 Next.js 14 Recoil Styled-components Firebase OpenAI GPT-4o

Hospital Guidance & Dispensing Robot Control System

mingkycarepro.site/medical · github.com/finalproject3fastcamp/mingky_care_pro

Aug 2026 · 6-person team project

  • Built the clinician dashboard, deriving each robot's status, destination, and battery from session events and splitting views by robot URL (/medical/:robotId).
  • Implemented the QR patient check-in flow (ROS2 node → FastAPI → guidance session) so that only robots activated by staff scanned QR codes and released themselves after repeated polling failures.
  • Cut wireless bandwidth for robot camera previews from 13.1 → 1.1 Mbps by sending only new frames at 640px, removing multi-second lag.
  • Built a LeRobot ACT imitation learning pipeline (29 episodes, 40,000 steps) and connected the policy that places pill bottles into bags to the pharmacy screen's packaging step on a real robot arm.
TypeScript React 19 FastAPI PostgreSQL ROS2 LeRobot (ACT)

GRE Vocab Master

apps.apple.com/app/id6758345755 · github.com/soojjung/gre-vocab-master

Jan 2026 — Present

  • Released a 1,560-word GRE vocabulary learning app to web and iOS using React 19 and Capacitor (WebView hybrid), maintaining the product through App Store v1.5.
  • Fixed a silent quiz-generation bug involving inflected word forms with regex normalization for 4 inflection types, reaching a 99.9% match in a full simulation across 1,560 vocabulary items.
  • Integrated Sentry across web and iOS after a Supabase auto-pause went unnoticed for 50 days, detecting and fixing new crashes within 3 days.
TypeScript React 19 Capacitor Supabase Sentry Tailwind CSS Vite PWA

Gacha Shop Map Service (GOTCHA)

apps.apple.com/kr/app/id6759491099 · github.com/soojjung/GOTCHA-FE

Jan 2026 — Apr 2026

  • Shipped a Capacitor-based iOS app to the App Store, applying a three-layer Container/Presenter architecture and hybrid state management (TanStack Query + Zustand) across 21 API hooks.
  • Optimized map API calls — viewport-based queries and a ‘Search this area’ button removed automatic refetching while panning, with a switch to a cluster API when zoomed out.
  • Managed architecture and coding standards as AI context (.ai/) to keep team conventions consistent, using AI for design review.
TypeScript React 19 Next.js 16 Zustand TanStack Query Capacitor Sentry

AI Policy Assistant for Newlyweds (bbumate)

bbumate.com · github.com/soojjung/bbumate-policy-chat

Oct 2025 — Dec 2025

  • Architected an end-to-end RAG pipeline using LangChain (LCEL) and ChromaDB, centralizing 113+ fragmented policies into a high-dimensional (4,096-dim) vector store.
  • Achieved a 66% reduction in system latency by implementing parallel document grading, reducing complex task processing times from 4.2s to 1.4s.
  • Engineered a fallback strategy (RAG → Query Re-write → Web Search) using the Tavily API, so questions outside the indexed data still get an answer through web search.
  • Developed a high-reliability grounding system with 97+ URL mappings, so every answer links to its official source.
Python FastAPI LangChain ChromaDB

Education

BSc. in Applied Mathematics and Statistics & Economics

Stony Brook, State University of New York — GPA 3.57 / 4.0

Graduated Dec 2018

Additional