Сергей

SERHII VOITOV
Python / Full-Stack Developer
[open contact info](look above in the "contact info" section) | [open contact info](look above in the "contact info" section) | [open contact info](look above in the "contact info" section) | github.com/diffary
Odesa, Ukraine • Open to remote worldwide

PROFILE
Full-stack developer with a strong backend focus. I build, test, and deploy production services end-to-end: FastAPI + async
SQLAlchemy backends, React/Next.js frontends, Stripe payment integrations, Celery task queues, and LLM-powered features —
all backed by 300+ automated tests and CI pipelines. Background in Computer Engineering (master's in progress) and 4 years of
C#/Unity game development, which gave me a solid foundation in OOP, algorithms, and shipping real products. AI-native
workflow — I leverage Claude and Gemini throughout development and critically review every output.

KEY HIGHLIGHTS
▸ 6 production-grade projects built end-to-end — from design docs to deployment and 24/7 operation
▸ 300+ automated tests across all projects (pytest, Vitest) with TDD methodology and GitHub Actions CI
▸ Complete Stripe payment cycle in production: Checkout, signature-verified webhooks, idempotent processing
▸ Deployed and operating services 24/7: systemd on Linux VPS, Vercel, multi-service Docker Compose
▸ Team collaboration experience: code reviews, shared codebase, API design discussions

TECHNICAL SKILLS
Backend: Python 3.10+, FastAPI (async), SQLAlchemy (async), Alembic, Pydantic v2, Celery, APScheduler, pytest, TDD
Frontend: React 18, Next.js (App Router), TypeScript, Vite, Zustand, TanStack Query, Tailwind CSS, Vitest
Data: PostgreSQL, Redis, Supabase, SQLite
Payments / Auth: Stripe API (Checkout, webhooks, idempotency), JWT, OAuth 2.0 (Google)
DevOps: Docker, docker-compose, GitHub Actions CI/CD, Vercel, systemd, Linux (Ubuntu), Nginx
AI / LLM: Claude Code, Gemini API, prompt engineering, LLM integration with structured output
Other: Git (branching, PRs, code review), C# (4 years, Unity), REST API design, asyncio

PROJECTS
DigiShop — Full-Stack Digital Commerce Platform ★ Flagship
Production-ready e-commerce platform for digital goods with a complete real-money payment cycle.
▸ Stripe Checkout integration with signature-verified webhooks and idempotent payment processing — tested with real
payments
▸ Async backend: FastAPI + SQLAlchemy async + PostgreSQL + Redis caching with rate limiting
▸ Automated order delivery and cleanup via Celery worker + beat scheduler
▸ JWT + Google OAuth 2.0 authentication, Alembic migrations, 5-service docker-compose stack
▸ 134 tests (TDD), full GitHub Actions CI pipeline
Stack: FastAPI, SQLAlchemy async, PostgreSQL, Redis, Celery, Stripe, React 18, TypeScript, Zustand, TanStack Query
github.com/diffary/digishop

Mail GenAIrator — AI Email Generation Web App ● Live
Web application that generates professional emails from topic, tone, and length parameters using Gemini LLM.
▸ LLM integration with provider abstraction, mock mode for development, and automatic rate-limit fallback
▸ End-to-end error handling, responsive UI with Tailwind + shadcn/ui
▸ Deployed and live at mail-genairator.vercel.app
Stack: Next.js (App Router), React, TypeScript, Tailwind, shadcn/ui, Supabase, Gemini API, Vercel

Telegram Task Scheduler Bot — AI-Powered Task Management ● 24/7 in prod
Multi-user Telegram bot where an LLM parses natural language into structured tasks with scheduled reminders.
▸ Free-text parsing via Gemini API with strict JSON schema validation and automatic retries
▸ APScheduler-based reminders with timezone support, multi-user isolation
▸ 86 tests, CI pipeline, deployed as a systemd service on Oracle Cloud (24/7 uptime)
Stack: Python, aiogram 3, SQLAlchemy async, PostgreSQL, Gemini API
github.com/diffary/BOT_telegram_scheduler

Resource Calculator — Full-Stack Desktop Application
▸ Crafting dependency tree builder with recursive DFS graph traversal and cycle detection
▸ 51 backend tests, packaged as a native desktop app via Tauri (.exe)
Stack: FastAPI, Pydantic v2, React 18, TypeScript, Vite, Tauri

Team Backend Project — Collaborative API Development
▸ Built a TTL/LRU cache layer that reduced external API calls by 3×
 ▸ Implemented O(log n) spatial lookup using scipy cKDTree for geolocation queries
▸ Collaborated in a shared codebase with pull requests and code reviews

EDUCATION
Master's — Computer Engineering | Odesa National Technological University | 2025 – Present
Bachelor's — Game Development & Interactive Media (VR) | ONTU | 2021 – 2025
4 years of C#/Unity development and full 3D production pipeline (Blender, Substance Painter, Unity). Thesis: rigged and
animated 3D tank model.

CERTIFICATIONS
Claude Code 101 — Anthropic (2026) • Claude Code in Action — Anthropic (2026)

LANGUAGES
Ukrainian (native) • Russian (native) • English (B1 — technical reading/writing, conversational)