Available for full-time roles

Sung Guk “John” Lee

Teacher turned full-stack developer.

Based in South Korea

Focus Full-stack web

Building Coco English

Coco English pronunciation drill asking the student to listen to the word fish, then record it.

Coco English speaking mission where Coco the cat asks what the student likes to do on weekends.

TypeScript/ JavaScript/ Python/ SQL/ Next.js/ React/ Flask/ Jinja/ PostgreSQL/ Supabase/ SQLite/ OpenAI APIs/ Azure Speech/ Vitest/ Playwright/ pytest/ Dependency Injection/ Vercel/ Supabase Auth & Storage/ Row-Level Security/ SQL Migrations/ Cron Jobs/ Git/ TypeScript/ JavaScript/ Python/ SQL/ Next.js/ React/ Flask/ Jinja/ PostgreSQL/ Supabase/ SQLite/ OpenAI APIs/ Azure Speech/ Vitest/ Playwright/ pytest/ Dependency Injection/ Vercel/ Supabase Auth & Storage/ Row-Level Security/ SQL Migrations/ Cron Jobs/ Git/

Selected work

Things I've built.

Coco English

Live

An AI app for practicing spoken English. Students record an answer and get feedback on what they said and how they pronounced it. I built it to replace the speech recordings I used to assign and collect one student at a time.

Try the demo

No sign-up. About 3 minutes. Needs a microphone.

View code on GitHub

Coco English welcome screen with Coco the cat cheering and a Try the demo button.

How it's built

Next.js App Router on Supabase/PostgreSQL
Separate teacher and student logins, enforced with row-level security
Azure Speech scores pronunciation; OpenAI handles evaluation and moderation
A content-addressed TTS cache keeps paid API costs down

Testing and stack

Backed by 1,200+ automated tests, including Playwright end-to-end coverage.

TypeScriptNext.js 15React 19SupabasePostgreSQLOpenAIAzure SpeechVercel

University IT Support Ticketing System

Group project

A role-based ticketing system for university support workflows, with separate dashboards and ticket queues for student, staff, and manager roles. Includes category-based routing, activity logs, a notification panel, and an automated pytest suite.

Primary contributor on a five-person team, authoring the majority of the backend and automated test suite.

PythonFlaskSQLiteJinjapytest

GitHub

Guitar Song Tracker

Live

A web app for keeping track of songs I want to learn on guitar. It stores the tuning, capo position, and a YouTube link for each one, plus how far along I am. Search and filter the library, or export the entire collection to JSON and import it again.

PythonFlaskPostgreSQLJavaScript

Live site GitHub

About

A short version.

I'm an ESL teacher and Computer Science graduate who builds full-stack software. I like turning problems I have seen firsthand into practical tools.

Nearly ten years of teaching taught me to explain hard things without jargon. That skill carries over to software more than I expected.

Stack: TypeScript, Next.js, React, Supabase/PostgreSQL
Currently: Seeking a full-time software role
Languages: English (fluent) · Korean (conversational) · Japanese (conversational)
Outside work: Boxing, guitar, lifting

Contact

Get in touch.

I'm looking for a full-time software role where I can work across the stack. If you're hiring, I'd like to hear from you.

Send me an email GitHub Resume