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Software engineer in London building React Native & Expo developer tooling — open to full-time roles, contract work, and collaboration.

I'm a software engineer in London working on React Native and Expo tooling — the layer that sits between the app and the device.

Across five years as a React Native engineer at early-stage startups, I've taken consumer mobile products 0→1 and 1→10: driving one from 1K to 10K DAU (30K MAU), cutting a main-screen load from 3s to 0.5s, and shipping the MVP that helped close a $150K seed round. Most recently I architected a cross-platform health-tracking app as a TypeScript monorepo — 95%+ code reuse across iOS, Android, and web — and led a team of five.

Alongside product work I build developer tooling. My main open-source project is serve-emu: the `npx serve` of Android devices. It spawns scrcpy on a booted emulator or attached phone, pipes H.264 frames over a WebSocket, and decodes them in the browser with WebCodecs, so you can stream and drive a real device from a browser tab — built for agentic mobile QA with tools like Claude, Codex, and Cursor, with REST input APIs, emulator GPS/route control, and logcat-over-SSE.

I also publish React Native libraries (react-native-focus-guide, a dependency-free tooltip and onboarding overlay) and contribute upstream — including merged fixes to Expo's expo-notifications and expo-task-manager R8 packaging, EvanBacon's serve-sim, and Spacedrive's spacebot.

I'm open to full-time roles, contract work, and collaboration on developer tooling.

Projects

Products, platforms, and prototypes.

serve-emu

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The `npx serve` of Android devices. Spawns scrcpy on a booted emulator or attached phone, opens an adb forward tunnel, pipes H.264 frames over a WebSocket, and decodes them in the browser with WebCodecs — so you can stream and drive a real device from a browser tab, locally, over LAN, or tunneled anywhere. Built for agentic mobile QA with tools like Claude, Codex, and Cursor. Exposes agent-friendly REST input APIs (tap/swipe/text/screenshot), emulator GPS + route playback (GPX/GeoJSON/KML), and logcat-over-SSE alongside the live view.

Published on npm as `serve-emu` — ~410 downloads in the last 30 days. Apache-2.0, written in TypeScript.

v1, actively developed

TypeScriptscrcpyWebCodecsWebSocketAndroidadbdeveloper-toolsagentic-QA

react-native-focus-guide

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A React Native library for interactive focus guides and tooltips — highlight any component with a dimmed overlay and anchor a tooltip to it, for onboarding flows and feature walkthroughs. Measures real tooltip size for accurate anchoring, supports 11 anchor positions with automatic on-screen clamping/flipping, is reactive to orientation, split-screen, and web resizing, and is Fabric / new-architecture safe. No native dependencies — pure JS across iOS, Android, and Web (via react-native-web).

Published on npm as `react-native-focus-guide` v0.2.0 — ~250 downloads in the last 30 days.

v0.2.0, maintained

React NativeTypeScriptonboardingtooltipiOSAndroidWeb

Proof

Milestones, rankings, and results.

Skills

The work Jiun is useful for.

React Native
Expo
TypeScript
WebCodecs & WebSocket streaming
Android device tooling (scrcpy / adb)
Kotlin
Swift

Work with Jiun

Selected advisory and build work.

Full-time engineering roles

Employment

Full time

Open to full-time software engineering roles — especially in developer tooling, mobile (React Native / Expo), or anything close to the device and runtime layer. London-based and flexible on setup: remote, hybrid, or onsite. Reach me at jiun.shin.uk@gmail.com.

Custom

Contract & freelance work

Contract

Flexible

Available for contract and freelance work: React Native / Expo apps and libraries, native iOS (Swift) and Android (Kotlin) modules, and developer-tooling builds like serve-emu. Flexible on location and engagement length — get in touch to scope it.

Custom

Open-source collaboration

Collaboration

Happy to collaborate on open-source developer tooling — especially React Native / Expo, device streaming and control, and agentic mobile QA. Open to contributions, co-maintenance, and building new tools in that space.

Custom

Email Jiun about a project

Experience

Roles Jiun has held.

Senior React Native Engineer · FutureworkLab

Nov 2024 – Present

Architected a cross-platform health-tracking app (iOS, Android, web) as a TypeScript monorepo — 19 feature modules, 657 source files, 95%+ code reuse. Integrated 6+ native health platforms (Apple Health/HealthKit, Health Connect, Google/Apple Calendar, Pedometer) with background sync for passive data collection. Lead a team of five engineers, setting coding conventions and code-review practices. Based in Seoul, Korea.

React Native Engineer · Sneakers

Jan 2024 – Jun 2024

Core React Native engineer at an early-stage consumer startup. Drove DAU from 1K to 10K (30K MAU) by owning performance and UX end-to-end — map clustering and location preloading cut main-screen load from 3s to 0.5s and reduced drop-off by 90%. Built a React admin dashboard with automated analytics that cut the Growth team's daily reporting from an hour to five minutes. Seoul, Korea.

Software Engineer · Gractor

Oct 2022 – Apr 2023

Cut the main dashboard's render time from 60s to 3s using clustering in Nuxt.js for performance optimization. Seoul, Korea.

React Native Engineer · Lighthouse

Feb 2021 – Oct 2022

One of the first mobile engineers — took core app features from concept to production under tight timelines and shipped the MVP that helped close a $150K seed round. Helped scale the engineering team from 4 to 13, mentoring new engineers and establishing best practices. Gyeonggi, Korea.

Education

Education.

National Institute for Lifetime Education

Jan 2021 – Dec 2024

B.Eng. in Computer Engineering (Academic Credit Bank System)