AI software studio · Sunmoon.co Pte. Ltd.
AI products, built by a founder who ships.
I'm Seunghun Lee — a SaaS founder and senior engineer (ex-Spotify, ex-Klarna). I design, build, and launch production AI agents, RAG systems, and full-stack SaaS for teams that need it done right the first time.
Flagship product
transcribe.soAn AI knowledge library: multi-model speech-to-text, cited Q&A, timestamped chapters, and an AI-agent API. Designed, built, and operated solo.
Built and shipped by an engineer who has done it at scale
- Spotify
- Klarna
- Worked with Y Combinator–backed startup
- Ex-Supabase Expert Partner
- transcribe.so
- goodlisten.co
What I build
Production AI, not prototypes.
Three ways to work together. Every engagement is hands-on — the person who scopes it is the person who writes the code and ships it.
Multimodal AI agents with RAG
Assistants that cite their sources, agents that take actions, retrieval over your own data. The same stack behind transcribe.so.
- Cited Q&A with real source attribution
- Tool-use and function calling
- Multi-model routing (OpenAI, Qwen, Mistral)
- Eval harness so quality doesn't regress
Full-stack SaaS, end to end
From schema to Stripe to ship. The product gets built by someone who has shipped and runs his own.
- Next.js + Postgres / Supabase
- Auth, organizations, and billing
- B2B and B2C ready
- Industry-standard stack, no vendor lock-in
Fractional CTO & AI consulting
Architecture reviews, model selection, and hands-on building. A CTO for hire who writes the code.
- AI / RAG architecture review
- Model and cost selection
- Hands-on implementation
- 6 months of email support on builds
Selected work
Products I've shipped and run.
Not case studies for clients I can't name — products I designed, built, and operate myself, plus senior engineering at companies you know.
transcribe.so
An AI knowledge library for lectures, podcasts, and videos. Multi-model speech-to-text, timestamped chapters, cited Q&A, subtitle export, and an AI-agent API that drops into ChatGPT, Claude, and Cursor. Ranked #4 of 80+ models on the ASR leaderboard. Designed, built, and operated solo.
- Multi-model ASR auto-routed per file
- Cited Q&A with timestamped sources
- 67 languages
- AI-agent API + MCP server
goodlisten.co
AI-powered podcast discovery plus a creator studio that turns long episodes into highlights, chapters, and clips in one click.
Spotify
Freemium — internal tooling and growth surfaces for one of the largest audio platforms in the world.
Klarna
Tooling Product Integrations — full-stack across the stack, pushing new tools and better ways of working.
Y Combinator–backed startup
Hands-on product engineering on a venture-backed product during its early scaling.
A note from the maker
Hey, I'm Seunghun 👋
In 2023 I left Spotify to work on finding the useful 90 seconds inside a three-hour podcast. We built goodlisten.co, ran out of runway, and I went back to a desk job.
But I kept building. transcribe.so came out of the same itch — I wanted production AI that actually shipped, not another prototype that dies in a notebook. Now I design, build, and run it solo: multi-model speech-to-text, cited Q&A, an AI-agent API, 67 languages.
sunmoon.dev is my studio (Sunmoon.co Pte. Ltd.). I take on a small number of builds for teams who need the same thing — production AI shipped properly. You work directly with me, not an account manager and a rotating bench of contractors. If I take your project, I'm the one writing the code.
— Seunghun
2
AI products shipped & operated
67
languages in production
10+ yrs
shipping full-stack software
1
engineer on your build — me
How it works
From idea to shipped, without the drama.
01
Scope
A call to understand the problem, the data, and the constraints. You leave with a concrete plan, a timeline, and a fixed-ish quote — not a vague proposal.
02
Build
I build in the open with short feedback loops. You see working software every week, not status decks. Architecture choices favor your team owning it later.
03
Ship
Deployed, monitored, and documented on an industry-standard stack with no vendor lock-in. A basic agent ships in 4–6 weeks; larger builds in 3–6 months.
04
Support
Six months of email support on every build, plus a discounted on-call package if you want me on speed-dial as you scale.
References
What engineering leaders say.
Seunghun has done a great job building internal software, provided positive energy and teamwork. He's a great team player and is very knowledgeable as a full-stack engineer. I highly recommend Seunghun.
Seunghun is known for his technical expertise, adaptability, and innovative mind — well-proficient across frontend and backend, moving between them based on the team's needs. His positive attitude and dedication consistently led us toward effective solutions.
Seunghun demonstrated a high level of proficiency and commitment, with exceptional skills in teamwork and problem-solving. He's always looking ahead, ready to tackle the next big thing, and reachable in times of need.
Throughout our collaboration, Seunghun consistently demonstrated a great ability to generate innovative ideas and contribute positively to the project and team. His dedication and creativity make him an asset to any team.
Engagements
Transparent pricing. No hidden costs.
Starting points, not fixed menus. Final scope and price come out of the first call.
Consulting / Fractional CTO
from $200/ hour
A CTO for hire who writes the code.
- Architecture & AI strategy review
- Model and cost selection
- Hands-on implementation
- Bug fixes and rescue work
AI agent with RAG
from $10k/ application
A production multimodal AI agent with retrieval.
- B2B / B2C SaaS ready, orgs + billing
- Cited Q&A and source attribution
- Industry-standard stack, no lock-in
- 6 months of email support
Full-stack SaaS
from $10k/ application
A complete SaaS build, schema to Stripe.
- Next.js + Postgres / Supabase
- Auth, organizations, billing
- Industry-standard stack, no lock-in
- 6 months of email support
Not sure which fits? Book a 15-minute intro and we'll figure it out.
Questions
Frequently asked.
Let's talk
Have something that needs shipping?
Tell me what you're building. If it's a fit, you'll get a plan and a quote — if it isn't, I'll tell you that too, and point you somewhere better.