Work Experiences

• - Software Engineer @ The Guild

  2025.09 ~ 2026.02

  Worked as a full-stack engineer at The Guild, a company operating a GraphQL-related SaaS product.

  As a full-stack engineer, I worked on small product features,
  and led a structural migration of the account system.

  • •Account Linking Migration
    • React
    • GraphQL
    • PostgreSQL
    • SuperTokens

    Enabled multiple sign-in methods to be linked to a single account.

    The product used SuperTokens to implement its authentication system,
    and one of its limitations was that each account could only have a single sign-in method.

    This encouraged users to create multiple accounts by signing up with different methods,
    which led to duplicated accounts with the same email and became a hurdle for future feature work and expansion.

    To address this, I implemented Account Linking at the application layer,
    independent from SuperTokens, so that multiple sign-in methods could be connected to a single account.

    For existing users with duplicated emails, I also led the account merge process by writing
    a DB migration script based on real production data and a wide range of edge cases.

• - Software Engineer @ Contents Technologies

  2024.07 ~ 2025.08

  Worked as a full-stack engineer at Contents Technologies, a company operating various businesses based on music IP.

  As a full-stack engineer, I developed mobile and web applications for a new business,
  and rewrote legacy software stacks for an existing business.

  • •BackPac
    • TypeScript
    • SolidStart
    • UnoCSS
    • urql
    • Rust
    • async-graphql

    Participated in the development of app and server for a new business targeting creator business.

    The app was initially developed targeting mobile devices using Capacitor,
    and during this process, to improve UX, I ported Stackflow,
    a stack navigation library, to Solid and utilized it.

    Later, the main target was changed to web,
    and to provide good UX in desktop environments while maximizing the use of existing code,
    I developed and utilized a plugin called stackflow-plugin-omniflow.

    Additionally, I participated in GraphQL API server development using Rust,
    and to improve frontend DX through the use of Semantic Nullability,
    I developed a support package for async-graphql and utilized it.

  • •Fluxus Infrastructure Rewrite
    • SolidStart
    • Solid Relay
    • TailwindCSS
    • Rust
    • lazycsv

    Proceeded with infrastructure rewrite work for Fluxus, a subsidiary related to music distribution.

    The existing infrastructure was developed through an outsourcing company,
    and as the business grew and data size increased,
    performance and scalability issues arose, leading to the decision for redevelopment.

    I actively participated from the stack research stage
    to ensure performance and scalability of the new infrastructure,
    and conducted high-performance OLAP PoC such as StarRocks
    and development of our own high-performance CSV parser lazycsv.

    Subsequently, I proceeded with development work centered on the frontend,
    and during this process, I developed an excellent web frontend in both UX and DX aspects
    by utilizing Solid Relay, a library I developed myself.

    Additionally, I proceeded with development independently without APIs
    by utilizing the Mocking functionality of GraphQL Tools,
    and during this process, I also took the lead in designing the GraphQL schema.

• - DX Engineer @ PortOne

  2022.10 ~ 2024.07

  Worked as a DX engineer at PortOne, a company building payment-related SaaS products.

  As a DX engineer focused on the frontend, I was responsible for, but not limited to,
  improving both internal and external developer experience.

  • •JavaScript SDK Rework
    • TypeScript
    • Node.js
    • SWC
    • esbuild

    Reworked the JavaScript SDK to improve performance, maintainability, and usability.

    Previously, the PortOne JavaScript SDK was a single fat script, with jQuery dependency,
    which resulted in poor loading performance and unnecessary overhead.

    I reworked the whole architecture with several priorities in mind like removing jQuery dependency
    and lazy loading support per each functionality of the SDK, while following business requirements like IE11 support.

    To achieve this, I constructed a custom module system that works without any ESM support.

    And I also configured a build system to transpile and bundle the core SDK and each functionality module,
    utilizing modern tools like SWC and esbuild.

  • •PortOne Analytics
    • TypeScript
    • React
    • UnoCSS
    • Framer Motion
    • Relay

    Involved in the development of a new analytics dashboard service for PortOne.

    I contributed to several parts of the product like creating custom chart components with SVG and Framer Motion,
    and integrating @defer support for Relay to utilize concurrent features of React 18.

    The chart components are made to match with high-quality standards that our team requires,
    focused on features like responsive design, animated transitions, and sticky axis labels.

  • •Payment Bridge
    • TypeScript
    • SolidStart
    • UnoCSS

    Created a custom checkout UI that gets embedded in customers' websites.

    Payment Bridge is a custom checkout UI that replaces the default checkout UI provided by payment gateways.

    To prevent customers from refusing to purchase due to poor experience,
    it is built with SolidStart to provide the best performance and UX.

    By utilizing features like streaming SSR and server RPC, it was possible to provide
    a smooth checkout experience that handles about 300,000 requests per month.

• - Backend Developer @ NutritionCourt

  2021.10 ~ 2022.10

  Worked as a backend developer at NutritionCourt, an AI healthcare startup.

  After previously leaving the company, I rejoined the team as a backend developer
  to fill the gap left by the departure of the previous backend developer.

  Despite being a backend developer, I also took on the role of maintaining the mobile app
  and onboarding new frontend developers, essentially working as a full-stack engineer.

  • •Welcoach App Development & Maintenance
    • Flutter
    • GetX
    • Node.js
    • GraphQL
    • Mercurius
    • Prisma
    • Elasticsearch

    Added features like simplified authentication and improved usability for the Welcoach app we had previously built.

    Although I joined as a backend developer, the company needed to continuously improve the app,
    and I was the only developer with deep product knowledge around it, so I took ownership of the maintenance work.

  • •API Backend for Welcoach Shop
    • Node.js
    • Fastify
    • Envelop
    • GraphQL
    • Schema Stitching
    • Terraform
    • AWS EKS, RDS, SQS, etc.

    Created an MSA backend for providing additional features to a Shopify store.

    Utilizing the Schema Stitching feature of GraphQL Tools, I created a single supergraph API
    that merges multiple microservices into a single API that can be used by the frontend conveniently.

    By integrating with the API provided by SBN, I created a service flow that allows customers to purchase
    a blood test appointment from the shop, take the test, and receive a report that is created with our own algorithm.

  • •Frontend Development Assistance for Welcoach Shop
    • Shopify Liquid
    • React
    • Svelte
    • Relay
    • Vite
    • WindiCSS
    • Astro

    Supported various frontend work that are required when building a Shopify store.

    On a web store built with Shopify, I did various customizations using vanilla JS and Liquid templates.
    I also created various custom components with Svelte to add dynamic functionalities.

    Moreover, to create pages for receiving questionnaires and displaying the reports,
    I utilized the Vilay framework, which I created as a side project to utilize React and Relay in SSR.

    Most of the development was done by collaborating with my teammates,
    and I also participated as a lead to help junior developers.

• - Frontend Developer @ NutritionCourt

  2020.09 ~ 2021.07

  Worked as a frontend developer at NutritionCourt, an AI healthcare startup.

  Due to the nature of a small startup, I also worked in various fields other than frontend.

  • •Rewrite Angular Project to Vue
    • TypeScript
    • Vue.js 2
    • Bootstrap 4
    • SCSS
    • Google App Engine

    Rewrote a MVP healthcare product from Angular 2 to Vue 2.

    I worked on an healthcare app that receives blood test results and displays report UI including meal plans.

    Responsive design was applied to the UI using Bootstrap 4 and SCSS.

  • •Rewrite Angular Project to Nuxt
    • TypeScript
    • Nuxt.js
    • Bootstrap 4
    • SCSS
    • Python
    • Falcon
    • Google App Engine

    Rewrote a B2B product from Angular 2 to Nuxt 2.

    I worked on a B2B product for hospitals that includes a desktop Web UI for doctors and a mobile Web app for patients.
    The app provided end-to-end features like scheduling appointments, writing reports, scheduling blood tests,
    receiving questionnaires, displaying reports, sending dosage reminders, etc.

    To perform SSR smoothly, optimization techniques like prefetching were applied.

    Also, I worked on the API backend a little bit, written in Python and Falcon. I mostly fixed bugs and added some minor features.

  • •Welcoach Mobile App
    • Flutter
    • GetX
    • Node.js
    • GraphQL
    • Mercurius
    • Prisma
    • Elasticsearch

    Created a mobile app that provides a health management solution based on blood test results.

    The app provides personalized meal plans and supplement recommendations by analyzing the blood test results
    that are retrieved using APIs provided by the National Health Insurance Service of Korea.

    I almost have worked on the app solely except for some infrastructure work,
    released the app to the Play Store, and downloaded more than 1000 times.