Denys Kotelnykov

Senior iOS Engineer / Team Lead

Contacts

Summary

Product-minded Senior iOS Engineer / Team Lead with 6 years of end-to-end delivery (idea → UX → architecture → implementation → release). Shipped 16+ own apps to the App Store and delivered multiple commercial products for iOS/iPadOS/macOS/watchOS. Strong in building high-performance, reliable, real-time apps and in automation of release/localization workflows.

Core strengths

  • Scale & reliability: high-load products, performance tuning (Instruments), crash-free improvement 80% → 99.9%, clean architecture (SwiftUI/UIKit, Combine/RxSwift).
  • Real-time & integrations: WebSockets, complex networking, external APIs (incl. Binance API / market data), offline-first & sync patterns.
  • Release & growth automation: internal tooling around App Store Connect API (auth, metadata export/import, app/version management, localization + screenshots upload), fastlane workflows.
  • Localization engineering: codebase string search, automated key generation, updates to localization files, refactoring hardcoded strings to localized APIs.
  • Deep platform work: Metal shaders, camera/editing pipelines, .pkpass tooling with on-device signing (OpenSSL in Swift).
  • Leadership: led teams up to 6 engineers, mentoring, cross-functional coordination (iOS / backend / design), delivery ownership.

Work Experience

Timrus Group — Project Manager & iOS Developer

Sep 2024 – Present
  • Owned planning and delivery: feature decomposition, prioritization, and cross-team coordination (iOS / backend / design).
  • Shipped and supported multiple products with different business models and technical constraints.
  • Selected products:
    • Coffee Talk — social networking app.
    • CollyHive — geek culture aggregator.
    • Wallet Creator — .pkpass editor with on-device signing (no backend).
    • Brusher — digital asset marketplace with adaptive UI, backend integration, analytics, and subscriptions.

Triada — iOS Developer / Team Lead

Aug 2022 – Aug 2024
  • Led iOS engineering for a high-load e-commerce product with millions of users.
  • Drove modernization: migrated Objective-C → Swift, moved UI away from Storyboards to UIKit, integrated payments.
  • Reliability impact: improved crash-free rate from 80% to 99.9%.
  • Managed a team of 5 developers; improved delivery workflow with custom Jira tooling.

Siazan — iOS Developer

Jan 2021 – Jul 2022
  • Built iOS apps from scratch: AdBlocker, VPN, TikTok-style short video app.
  • Worked end-to-end: implementation, iteration, and delivery.

Midland Retail Group — iOS Swift Developer

Sep 2019 – Dec 2020
  • Developed Numbers — VoIP client with Realm sync, WebSocket chat, and audio/video calls.

GameTrek — Unity3D Developer

Jan 2019 – May 2019
  • Optimized gaming services for TELE2.
  • Designed RTS mechanics and quest systems (Walk the Talk, Secret Government).

Selected Projects

OverCam — camera + reference overlays + on-device AI editing

  • Built a full camera stack with manual controls and composition overlays; designed UX for “repeat the reference shot precisely”.
  • Added on-device AI editing: relighting, background changes, retouching, artistic filters.
  • Links: App Store • Website

EasyWallet — offline .pkpass editor with local signing

  • Built a standalone .pkpass generator/editor with on-device signing (no backend dependency).
  • Bundled OpenSSL into a Swift framework and executed signing workflow directly from Swift.
  • Links: App Store

Lapy — high-load e-commerce (Tech Lead)

  • Scaled product handling 5,000 users/hour; built dynamic product lists (UIKit + diffable data sources) and complex checkout flows.
  • Led tech + process in a 20+ person team: internal tooling, task tracking, KPI monitoring, planning syncs.
  • Links: App Store

NanoApps: AI App Generator — prompt → mini apps on-device

  • Generates mini “calculator-style” apps from a prompt; stores and runs them locally.
  • Parses JavaScript and renders UI natively via a custom interpreter + custom UI system.
  • Links: App Store

WatchFace Notes — notes on Apple Watch with real-time sync

  • Built Apple Watch notes app with seamless sync across iOS/iPadOS/macOS.
  • Supports watch-face note creation + widgets on iPhone and macOS.
  • Links: App Store

Xcstringer — macOS .xcstring localization tool

  • AI-assisted translation workflow for .xcstring: generation + parsing + automation to speed up localization.
  • Links: App Store

Additional shipped apps (selection)

Skills

iOS / Apple platforms
  • Swift • SwiftUI • UIKit • Combine • RxSwift • SnapKit • Texture (AsyncDisplayKit) • StoreKit
Data / Networking
  • GRDB • Realm • SwiftData • SQL • REST • WebSocket • Alamofire
Quality / Performance
  • Instruments • Performance monitoring • Memory leak tracking Architecture design • Clean Architecture • MVVM
Monetization / Analytics
  • Subscriptions • RevenueCat • Adapty • Analytics
Backend / Infrastructure
  • Vapor (Swift) • Firestore • NodeJS
Product / Collaboration
  • Team leadership • Mentoring • Hiring • Cross-functional coordination • Jira • Git
Design / Other
  • Figma • Zeplin • UI/UX • Spline • Unity3D

Education

Kharkiv National University of Economics (2018) — Bachelor’s Degree in Economic Informatics and Information Systems