Freelance Flutter & Cloudflare development
I am Seongjin Kim, a full-stack developer. I build Flutter apps and Cloudflare-based backends, and I write about that work on this blog.
- 10 years
- building software
- 11
- commerce apps
- 3
- B2B full-stack
- AI
- chat app shipped
What I can take on
Mobile apps (Flutter)
iOS and Android from one codebase — commerce, diary, social, subscriptions, in-app payments, push, deep links. Ship a new app, or take over one that already exists and make it stable.
AI products & features
Character chat, LLM API integration, streaming responses, prompt pipelines, token cost control. Built and shipped, not a proof of concept.
Backend & edge infrastructure
Cloudflare Workers · D1 · R2 · KV · Durable Objects, and AWS. APIs, cron jobs, webhooks, OAuth integrations, queues — running without a server to babysit.
B2B & full-stack
Admin dashboards, internal tooling, third-party API integrations, permission models, and the unglamorous reliability work around them.
Cloud cost reduction
Find where the bill actually comes from and move that part — egress, always-on instances, managed services you are paying for twice.
Rescue & handover
An app whose original developer is gone, a codebase nobody wants to touch, a service that falls over weekly. I have picked up all three.
Selected work
- LumoraCharacter chat AI app — conversational AI product built and shipped.
- Diary appConsumer app with daily-use retention as the core problem.
- Commerce apps · 11Storefront, cart, payments, order flow, push and deep links.
- B2B full-stack · 3Internal tools and dashboards, end to end.
- effidev publishing automationThe service linked from this site — OAuth to five platforms, scheduling, media pipeline. Built and operated by me.
Client projects are listed by type — names are under NDA unless the client has made the work public.
You can see how I work before you ask
The publishing automation linked from the home page — scheduling to Instagram, Threads, X, YouTube and TikTok — is mine, built and operated end to end. The posts on this blog come out of that work and out of client projects, with the versions, numbers and code checked against primary sources. Read a few and decide whether that is the kind of engineer you want.
Get in touch
Instagram DM is the fastest. Email works too — I read both.
Including these makes the first reply useful
- What you are building, and what problem it solves
- Where it is now — idea, existing code, or a live service
- Rough timeline and budget range
- Platforms and any stack you are locked into
If it is not something I can do well, I will say so rather than take it on.