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About the Expert

Built personally by James, a 23-year veteran

A full-stack AI & dev expert with 8.5B KRW cumulative revenue and 350+ shipped projects handles everything from planning to deployment

James Profile

James (Sunghoon Lee)

23-Year Full-Stack AI · Dev Expert

Yonsei University, Computer Science Luxury Commerce Startup CTO (₩2B raise, M&A exit) Founded a 30-person agency [Insomnia]

₩2B annual revenue, ₩8.5B cumulative — hundreds of complex platforms shipped

Using AI agents to handle more work than a company of dozens of employees

3,000+ students trained in development, vibe coding, and entrepreneurship

Repeat judge for government startup programs and hackathons

heyjames YouTube

20K+ Subscribers

#Startups #Marketing #VibeCoding #DevTips #Outsourcing

최근 추천 영상

Subscribe to YouTube Channel

Why you should work with James

Built hundreds of startup platforms — combining a developer's eye with a founder's perspective.

Ran an agency to 8.5B KRW in revenue. Sales, contracts, operations — all hands-on experience.

Through hundreds of projects, James has built deep domain knowledge across legal, tax, real estate, advertising, education, startups, monetization, programming, infrastructure, and AI.

First delivery
24 hrs
Projects shipped
0
Total Revenue
0
Program Rating
4.7/5
Why Rails

Why James builds on Ruby on Rails

While JS full-stacks like React, Next, Vercel, and Supabase evolve in fragments, Ruby on Rails has settled into the strongest single-person full-stack for shipping a SaaS end-to-end. The gap only widens in the AI era.

AI-friendly

The stack AI builds fastest

  • Same feature in roughly 1/5 the code
  • More fits in the AI's context — fewer hallucinations and rework
  • Faster and more accurate than React + Express + Prisma

Code volume to deliver the same feature

Rails
JS full-stack
Full-stack built-in

One Rails instead of 100 libraries

  • Long AI calls and email run on Solid Queue
  • Realtime chat and notifications via built-in WebSocket
  • Subscription billing and recurring jobs on a built-in scheduler
  • Frontend, DB, cache, and storage in one package
Auth Background jobs WebSocket Scheduler Hotwire DB Cache Storage
Single server

One server runs the whole SaaS

  • One VPS in Seoul region runs DB, files, scheduler, and web
  • Operate for around $10/month until traffic really grows
  • No stacked bill for Vercel + Supabase + Upstash + Resend + S3

Operations setup

Rails
  • • Everything inside one VPS
JS full-stack
  • • Vercel (hosting)
  • • Supabase (DB · auth)
  • • Upstash (queue · cache)
  • • Resend (email)
  • • S3 (storage)
Security

Out of the npm supply-chain blast radius

  • Fewer dependencies = smaller attack surface
  • Auth · CSRF · SQL injection · sessions handled by the framework
  • API keys stay server-side — never leak to the client

Average dependencies in production

Rails

~30 gems

VS

React / Next

~1,500 npm

Solo-friendly

One person ships end-to-end

  • Rails: 1 person owns product → ops
  • JS full-stack: FE · BE · DevOps · DBA split
  • The secret behind shipping in 4 hours

Roles required

Rails

👤 × 1

JS full-stack

👤 × 4

Maintainable

Same shape one year later

  • Rails conventions: same for 20 years
  • Code AI wrote a year ago still composes cleanly today
  • Successor handoff takes a fraction of the time

How often core frontend tooling churns

Rails Stable for 20 years

MVC · ActiveRecord · ERB

React Swaps every 1–2 years

Router · State · Bundler

Rails 로 만들어진 회사들

AI 시대에도 살아남은 풀스택 — 세계 최대 코드 호스팅부터 국내 대표 서비스까지, 같은 프레임워크 위에서 운영되고 있습니다.

해외
  • GitHub

    세계 최대 코드 호스팅

    Microsoft 75억 달러 인수
  • Shopify

    글로벌 이커머스 플랫폼

    시총 약 1,500억 달러
  • Airbnb

    글로벌 숙박 공유

    시총 약 850억 달러
  • Stripe

    온라인 결제 인프라

    기업가치 약 700억 달러
  • Twitch

    라이브 스트리밍

    Amazon 9.7억 달러 인수
국내
  • 당근마켓

    지역 기반 중고거래

    기업가치 약 3조 원
  • 마이리얼트립

    여행 예약 플랫폼

    누적 거래액 1조 원+
  • 리멤버

    비즈니스 네트워크

    드라마앤컴퍼니 · 가입 400만+
  • 업비트

    암호화폐 거래소

    두나무 · 국내 1위 거래소
  • 잡플래닛

    기업 리뷰 · 채용

    기업 리뷰 600만+ 건
FAQ
Q

Can you build apps too?

A

Yes — as hybrid apps.

We build the mobile web first, then package it as an app. The single build runs across desktop browsers, mobile browsers, iPhone apps, and Android apps with the same UX and feature set. No need to build for four environments separately.

Toss and Karrot, along with many leading services in Korea and abroad, are already built and operated as hybrid apps.

Desktop Web

Mobile Web

iPhone App

Android App

one build · one UX · one feature set

Native features still work

Push notifications, in-app purchases (App Store / Play Store), camera and contacts access — anything that only works inside a mobile app is implemented alongside.

Packaging tech

We pick from Hotwire Native, Flutter, or React Native — whichever fits the service best.

Hotwire Native Flutter React Native
Why It Works

Why non-developers can't get to launch

There's a repeating pattern to why people learn vibe coding but never actually launch. Breaking that pattern is at the core of how James works.

Common failure pattern

  • People keep adding features without setting any operating policies.

  • Security and risk reviews are skipped entirely.

  • Multiple features get built at once, conflicting with each other.

  • Each feature moves on before being reviewed or covered by tests.

  • Ideas get explained to the AI in whatever order they come to mind.

How we actually work

  • We split the work into the right unit and build one step at a time.

  • After each build, we review the code and write tests.

  • Risky pieces get verified in a simple structure first, then merged into the main flow.

  • Each new feature is layered on top of verified ones for safe growth.

  • We analyze the plan and structure it technically so the AI understands it clearly.

Yours to keep

Take it over and run it yourself with vibe coding

We hand the deliverable over to your team and guide you so you can modify and operate it yourself with vibe coding.

Source code repository

We hand over the entire source code, repository and all — it's fully your asset from day one.

AI agent setup & usage

From installing the AI agent that edits your code to using it in practice.

Editing code & deploying

The full flow of changing features yourself and deploying to production.

Testing & detailed code walkthrough

How to test, plus a detailed explanation of the code's structure and behavior.

Database specification

The data structure and table relationships, documented and handed over.

Client reviews

What a founder who built it with us says

Real words from a founder who built their own service with HeyJames.

“What amazed me most was being able to build just by describing what I wanted, even without knowing how to code. Whenever I left a request, an updated result came back in no time.”
“Every question got answered right away, so I never got stuck or left wandering on my own.”
“I signed up drawn by the promise of seeing results fast — and it really was that fast, so I was glad I chose this. Other places quoted timelines that were just too long.”
“Everywhere else quoted tens of millions of won, while this was pay-later and only a few million — at first I was skeptical. It exceeded my expectations and I was thrilled.”
“The moment I saw the result, 'wow, this is great' just came out. Even the landing page came out clean and polished — I was surprised.”
“It had even built parts I hadn't thought of. You get not just what you asked for, but more.”
“Working directly with the founder meant no middlemen and instant communication — that earned my trust.”
“The progress was organized so systematically that I could always see at a glance what was done and what was left.”
“I've already shown it to peers in my startup program, telling them 'you should try this.' I confidently introduced it as something that builds your prototype fast.”
“I don't want this to be a one-off — I'd love to keep going with maintenance and further development. That's how much I trust them.”
“Seeing the result made me so eager to launch that I could hardly wait. That's how excited I am.”
“They handed over the source code and even walked me through how to run it, so I ended up editing and deploying changes myself. It's not a dead-end handoff — I can keep growing it on my own, and that's what I loved most.”
Portfolio

James keeps shipping products

Not just teaching or consulting — James ships his own products the same way. Every one is fully built including the admin panel and ready to operate.

Hey James

heyjames.ai

Built-in features

Main features delivered (by effort)

  • Video courses + progress tracking
  • Toss Payments recurring billing (membership)
  • 1:1 consulting booking + terms checkout
  • Community posts, comments, likes
  • Streaming AI chatbot
  • i18n (Korean / English / Chinese)
  • Admin panel (courses, payments, users, ads)
  • Unicorn calculator + dynamic OG image

Built-in features

Main features delivered (by effort)

  • Text → slide video auto-generation (Remotion)
  • AWS Lambda distributed video rendering
  • TTS voice synthesis (multiple voices)
  • Turbo Stream live progress
  • Meta/Google ad auto-upload manager
  • Payment + credit system
  • Shared-server SaaS child app hosting
  • Admin panel

Built-in features

Main features delivered (by effort)

  • Studio / instructor / class search
  • Live class streaming
  • Booking + payment
  • Instructor payout system
  • Reviews & ratings
  • Studio self-registration portal
  • Admin panel

Built-in features

Main features delivered (by effort)

  • Gmail auto-collection + AI parsing
  • Claude-based rate suggestion
  • Counterparty classification (direct/agency/speculative)
  • YouTube Data API metrics
  • Review → live → payout workflow
  • Google OAuth sign-in
  • Admin panel

Built-in features

Main features delivered (by effort)

  • AI live Q&A SSE streaming (Claude)
  • Monk / Friend persona modes
  • Prompt caching cost optimization
  • Today's dharma talk (date-based content)
  • Buddhism ABC: 8 doctrine cards
  • Conversation history

Built-in features

Main features delivered (by effort)

  • AI live Q&A (Yoga Sutras persona)
  • Today's sutra card
  • Sutra library (with Sanskrit original)
  • KakaoTalk share cards
  • Premium subscription scaffolding

Built-in features

Main features delivered (by effort)

  • Vision LLM palm analysis (image upload)
  • Physiognomy + palm compatibility
  • Saju (Four Pillars) reading
  • Result card PNG export (9:16 / 1:1)
  • Auto photo deletion policy (PIPA-compliant)
  • Google OAuth sign-in

Built-in features

Main features delivered (by effort)

  • AI dream interpretation (Korean traditional interpreter persona)
  • FAL.ai flux-2 illustrations (3 styles)
  • Active Storage S3 persistent images
  • Anonymous public feed + reactions
  • Web Share API
  • Per-call AI cost tracking

Built-in features

Main features delivered (by effort)

  • Bank of Korea ECOS indicators auto-collection
  • Open Assembly 22nd-term bill tracking
  • Ministry of Land real-estate transaction charts
  • Policy Briefing RSS integration
  • NEC pledge evidence auto-matching
  • D+N timeline visualization from inauguration
  • Email / Google OAuth auth
  • Admin evidence review tool
FAQ

Frequently Asked Questions

The questions clients ask most often before commissioning a build.

Q How long does development take?
A

We work in focused 4-hour sessions, and core features — payments included — are usually done within one or two sessions. Every session ends with the result deployed to a server, so you always receive something that actually runs.

Q Our plan isn't finalized yet — can we still commission a build?
A

Yes. With AI, the cost of writing code has dropped so much that building an MVP first and refining it in use beats perfecting a spec up front. Features are prioritized and built in stages, and if you know your own business, that is the plan — no separate product planner needed.

Q Can we trust the quality of AI-written code?
A

In the AI era, verification matters more than writing. On top of automated tests, a developer with 23 years of experience reviews everything, we walk through features together on screen share during sessions, and you test them yourself. Most issues found are fixed within a prompt or two.

Q Why is it cheaper than typical agencies? I've heard cheap outsourcing is risky.
A

Risky low prices come with three signals — a quote given without any questions about your requirements, starting work without a contract, and no plan for after launch. heyjames does the opposite of all three. Our price is lower for one reason: deep AI leverage and 23 years of experience mean the same work takes us less time.

Q When does the 100% refund apply?
A

You can cancel the session any time within the first 30 minutes after it starts, and if you do, we refund the full amount you paid. If we can't show you a satisfying result within those first 30 minutes, we return 100% of your payment — no questions asked. That's how confident we are in the outcome.

Q Does changing things later cost a lot?
A

Unlike traditional outsourcing, there's no per-change quote. Because we bill by build complexity and difficulty, you don't have to lock the scope in advance — request and change as much as the time allows, and a reference screenshot is usually all we need to build the screen you want.

Q How is the pay-later build billed?
A

There's no upfront payment. Cost is based on the complexity and difficulty of the build. Your project page shows clear per-item pricing — the initial build and each change request as separate line items, with a running total. You're only billed for feature changes and additions; bug fixes are always free.

Q When do I pay for a pay-later build?
A

Once the unsettled balance reaches 2,000,000 KRW, you settle before the next change request can proceed. Until then you can keep requesting changes without paying. With many revisions the total bill can exceed 2M KRW — in that case you simply settle in 2M increments and keep going. You can also pay early anytime to receive instructions for the source code and usage guide. Payment is by bank transfer, processed as soon as the deposit is confirmed.

Q When do I receive the pay-later build deliverables (source code & guide)?
A

Your app is deployed to a test server, so you can use it right away — even before paying. We'll send instructions for the full source code and usage guide once the accumulated balance is settled.

Q How does the contract work?
A

We only work with a standard written contract. It explicitly covers copyright and source-code transfer, acceptance criteria and review period, the scope of free defect repairs, and the change-request process. Under court precedent, copyright stays with the developer unless the contract says otherwise — wherever you commission work, check for that clause. We include it up front.

Q What about maintenance after launch?
A

Development is followed by an annual maintenance contract. Change requests and questions are handled against a time balance, we hand over documentation when the contract ends, and if you hire a developer we'll walk them through the code.

Q What's the difference between defect repair and maintenance?
A

Defect repair means fixing, free of charge, anything that was contracted to work but doesn't — provided for 6 months after delivery. New features and improvements are maintenance (paid), with scope, response time, and cost defined in writing before we proceed. Keeping the two separate in the contract is what prevents disputes later.

Q We don't know how to code — can we edit and operate it ourselves later?
A

Yes. If you'd like, we set up an AI coding environment (Claude Code) on your machine and train you to use it. No need to study code — copy and screen tweaks can be done with prompts, and anything you get stuck on we sort out together in a session.

Q Do you build in payments too?
A

Yes. As a Toss Payments partner we help you apply with the sign-up fee waived, and we implement both one-time and subscription payments. We build against test keys first — swap in your keys and real payments go live.

Q Can the server handle it when users grow?
A

We build so that a server costing a few dollars a month handles tens of thousands of users. Because we use a proven full-stack framework instead of stacks whose bills explode with usage, you simply upgrade the server step by step as you grow.

Q Can we pay with government startup-program funds?
A

Yes. We prepare the paperwork such programs require — outsourcing contracts, development plans, and completion reports. With extensive experience both judging and delivering government-funded projects, we work to each agency's requirements. We also issue the full set of settlement documents — statements of work, photo-documented inspection reports, and tax invoices — and handle prior-approval and multiple-quote procedures for larger contracts.

Q Can we get the source code of the service you build?
A

Yes. Every service we build is a standard Ruby on Rails web application with no platform lock-in. You can receive the full source code as-is, and we can push it to your own GitHub repository so future changes are tracked there too. Separately from handing over the code, copyright transfer is written into the contract — receiving the files and receiving the rights are legally different things.

Q Can it integrate with systems we already use, or an engine we built ourselves?
A

Yes. We support outbound API calls, webhooks fired on events, and connecting your own engine (Python or otherwise) as a separate API server. We can also build a public API with an OpenAPI schema so AI agents like Custom GPT Actions can call your service.

Q Where are our data and uploaded files stored?
A

The initial version is stored in dedicated storage on servers we operate in Korea. When you move to production, we migrate the database and file storage to cloud infrastructure you own (e.g. AWS Seoul region).

Q Is data safely separated per company or per customer?
A

Yes. The app is designed as a multi-tenant system where every query is scoped to the signed-in account's company, blocking cross-company access at the code level. If you need a physically separate database or server, we can set that up as a dedicated build.

Q When we delete a file or record, is it really deleted?
A

Yes. Deleting removes both the database record and the actual file in storage immediately. Backup retention and disposal policies are designed around your privacy requirements.

Q Can the HEY JAMES team see our data?
A

The service has no screens for browsing client data, and server access is used only for operations such as incident response. Once you migrate to infrastructure you own, your data is entirely under your control.

Q How are secrets like API keys managed?
A

Sensitive values such as API keys and passwords are managed with encrypted configuration files (Rails encrypted credentials), with the decryption key stored separately. Nothing is stored in plain text in the database or source code.

Q When we go to production, do we own the domain, database, and storage?
A

Yes. The domain is registered under your name, and the database, file storage, and backups are all migrated to your own accounts. Test accounts and demo data are cleaned up at handover.

Q What happens to the service when our engagement ends?
A

Copyright, source code, server and domain accounts, and deployment docs are all transferred to your name, so the service runs perfectly well without heyjames. You can maintain it yourself, hire another agency, or come back for spot requests. Not locking you in is the principle.

Start now — the easy way in

Go slow with pay-later and no upfront cost, or fast with a focused 4-hour real-time build. Pick what suits you.