Full Stack Developer · 4+ years shippingHi, I'm Khánh I build systems that do real work.
Full-stack developer rooted in Golang backend for high-scale fintech. Payment systems processing millions of daily transactions, real-time ride-hailing, and AI-powered SaaS — built end to end. Hà Nội, Việt Nam.
Hà Nội, Việt Nam · ICT (UTC+7)
Available for new projects
- find an engineer who ships
- Found 1 match: Nguyễn Duy Khánh
- 4+ yrs · Golang · Node · TS
- 10M QR payments daily
- ChillGo — real-time rides
- IELTS Smart — AI scoring
- Available for new projects
- hire him
Companies I've shipped for
What you can hand me.
The high-scale backend, the real-time layer, or the whole product. All three work.
High-scale backend & payments
Golang services built for volume: QR payment systems generating 10 million codes a day, e-invoice platforms dispatching 20,000 invoices daily, integrations with VIB, BIDV, VietinBank and Vietcombank, CDC pipelines, and reconciliation that balances to the đồng.
Real-time systems & mobile
Driver matching, live location tracking, and trip lifecycle for ride-hailing — Golang, Redis and FCM broadcasts, with background job workers and fare reconciliation. Shared Flutter apps for riders and drivers, plus the web admin console to run it all.
AI products, end to end
IELTS Smart scores Speaking and Writing with LLM evaluation and a pronunciation analysis pipeline — plus tiered subscriptions with per-feature quotas, a credit-based B2B scoring API, and admin dashboards. Go and PostgreSQL underneath, Next.js on top.
Products I helped build.
From payment rails to ride-hailing — real systems in production, with real users.
IELTS Smart
AI-powered SaaS for IELTS Speaking & Writing practice and mock tests, for both learners and centers (B2C & B2B). Automated band scoring via LLM evaluation, plus a pronunciation and speech-analysis pipeline for Speaking.
End to end — the scoring pipeline, tiered subscription & billing with per-feature quotas, a credit-based B2B Partner Scoring API, center/admin dashboards, i18n, JWT auth, and audio upload via Cloudflare R2.
- Go
- PostgreSQL
- Next.js
- LLM
- Speech analysis
- Cloudflare R2
- JWT
- i18n
KPOS
UpcomingA sales management system for retail stores: product catalog with variants and price books, stock and stocktakes, purchasing and orders, plus customers, staff, attendance and payroll — multi-branch from the start.
Building it end to end — the catalog and inventory model, CSV import/export, branch-scoped access, and the admin console on top.
- Golang
- Next.js
- TypeScript
- PostgreSQL
- Multi-branch
ChillGo
A ride-hailing platform: real-time driver matching, live location tracking, trip lifecycle, and fare & revenue reconciliation.
End to end — matching and tracking in Golang with Redis, FCM broadcasts, background job workers, deep links, shared Flutter apps for riders and drivers, and a web admin console, on Clean Architecture.
- Golang
- Redis
- Flutter
- FCM
- Clean Architecture
Frame by Frame Player
A fully offline iOS app for motion analysis, built for coaches, athletes, physios and animators. Ordinary players scrub in whole seconds, so a golf swing or a lift can never be inspected — this one makes the frame the unit of work: step one frame at a time, overlay the neighbouring frames as an onion-skin motion trail, and annotate the exact frame.
Built the app — an on-device FFmpeg extraction pipeline with pre-flight memory estimation and cancellable sessions, onion-skin ghosting up to five frames each way colour-coded by direction, an annotation layer rendered in a background isolate so exports burn in cleanly, RevenueCat subscriptions, eight locales, and the App Store submission itself. No accounts, no backend, no analytics — nothing leaves the device.
- Flutter
- Dart
- FFmpeg
- RevenueCat
- StoreKit
- Next.js
- i18n
Payment System
High-capacity QR code generation producing 10,000,000 codes daily, with real-time transaction notifications — integrated with VIB, BIDV, VietinBank and Vietcombank.
Backend — the generation pipeline, bank integrations, and the real-time notification flow, in high-traffic production.
- Golang
- Kafka
- PostgreSQL
- Bank APIs
E-Invoice System
E-invoice calculation and dispatch for partners including VIETTEL, VNPT, MISA and FPT — 20,000 invoices a day for 1,000+ users.
Backend — CDC for asynchronous processing, calculation, and dispatch that has to be right the first time.
- Golang
- CDC
- Kafka
- PostgreSQL
Nail System
A multi-branch nail salon management platform: booking management, employee scheduling, inventory control, and role-based access.
Full stack — built with NestJS, TypeORM and MySQL, with RBAC and JWT authentication.
- NestJS
- TypeORM
- MySQL
- JWT
- RBAC
Four years of building for fintech. Still not bored.
I'm a full-stack developer rooted in backend work — the kind where correctness matters: a payment that must settle, a driver who must be matched in seconds, an essay that deserves a fair score. My happy place is Golang, PostgreSQL, Redis and Kafka, but I'll go wherever the bug is.
I shipped my first production code in 2021 and haven't stopped since. I've built QR payment systems producing 10 million codes a day, an e-invoice platform dispatching 20,000 invoices daily for VIETTEL, VNPT, MISA and FPT, a lending platform connecting merchants with banks, and messaging gateways with CDC for reliable delivery.
These days I build products end to end: a ride-hailing platform with real-time matching in Golang and Flutter, and an AI-powered IELTS scoring SaaS in Go, PostgreSQL and Next.js — from schema to screen, ideation to ship.
Most of what I'm learning and breaking ends up on GitHub (opens in a new tab).
A few quick bits:
- B.IT — Posts & Telecoms Institute of Technology
- Based in Hà Nội, Việt Nam (ICT)
- Backend-leaning full-stack, Golang first
- +45% test coverage on a 100k-user product
- Distributed systems reader
- Ships mobile too — Flutter, both apps
One last thing: I'm open to new projects right now. Say hello — I don't bite.
The tools I reach for.
Four years of picking things up and putting a few down. These are the ones I'd be happy to be judged on.
Backend
Where most of my time goes.
Golang
Node.js
NestJS
Express
gRPC
Data & Messaging
Relational, document, cache and stream.
PostgreSQL
MongoDB
Redis
Kafka
MySQL
Frontend & Mobile
Enough to ship the whole thing.
JavaScript
TypeScript
React
Next.js
Flutter
Tooling
Build it, test it, ship it.
Git
GitHub
GitLab
Python
Four years, three chapters.
Agency developer, then high-scale fintech, now products end to end. Here's the honest summary — the full version is in the CV.
Full-stack Developer
Chill Go Viet Nam Technology JSC · Hà Nội
- Built real-time driver matching, location tracking, and trip lifecycle for a ride-hailing platform (ChillGo) using Golang, Redis and FCM broadcasts.
- Implemented Clean Architecture, standardized API responses, background job workers, fare calculation, and driver revenue reconciliation.
- Developed shared Flutter apps for riders and drivers, plus a web admin console for managing users, drivers, trips, and catalogs.
– Present · 1 yr 1 mo
Backend Developer
KiotViet Corp. · Hà Nội
- Developed and maintained backend services and APIs in Golang, efficiently handling high-traffic environments with over 100,000 active users.
- Integrated third-party services seamlessly, enhancing functionality and user experience across multiple platforms.
- Implemented comprehensive unit testing, increasing test coverage by 45% and significantly reducing bug rates in production.
– · 3 yrs 1 mo
Backend Developer
Greenify Viet Nam Co. · Hà Nội
- Engineered scalable codebases with NodeJS and ReactJS, focusing on performance and maintainability.
- Designed databases to meet project requirements and ensure functional effectiveness.
- Seamlessly integrated third-party services, extending application features and improving user experience.
– · 1 yr 4 mos
Questions people ask before hiring me.
Short answers. Anything else, email me.
How do we work together?
A short call to pin down the real problem, then a written plan with milestones before I write any code. After that you get working software every week — not a status update.
What kind of work do you take on?
Backend-heavy products are my sweet spot — payments, real-time systems, integrations — but I ship the whole thing when needed: web in Next.js, mobile in Flutter, and the Golang services underneath.
Can you build AI features?
Yes — IELTS Smart scores Speaking and Writing with LLM evaluation and a pronunciation analysis pipeline, with quotas and billing wired in from day one. I build AI features that survive real users and real bills.
What do you build with?
Golang first, with Node.js and NestJS where they fit. PostgreSQL, MongoDB, Redis and Kafka for data; Next.js and TypeScript on the front; Flutter for mobile. If your stack is something else, tell me — I'd rather say it's not a fit than learn on your budget.
Where are you based, and will our hours overlap?
Hà Nội, Việt Nam — ICT (UTC+7). That's a full working day with Asia-Pacific, afternoons with Europe, and evenings with the US West Coast. Chat and email day to day, calls when a call is faster.
Are you free, and how do we start?
Yes, I'm open to new projects right now. Email khanhnd4.work@gmail.com with what you're building and when you need it — if it's a fit, you get a plan and a timeline back; if it isn't, I'll say so.
Got something you want built?
Tell me what you're working on. I'll tell you honestly whether I'm the right person for it — and what it would take.
You'll also find me here.