Nazar Kozak
Verified Expert in Engineering
iOS Engineer and Developer
Los Angeles, CA, United States
Toptal member since March 3, 2025
Nazar is a skilled senior iOS engineer with 10+ years of experience in mobile development, specializing in Swift, SwiftUI, UIKit, ARKit, and AI-powered apps. He has built scalable iOS applications, led teams, and integrated advanced features like computer vision, augmented reality (AR), and LLMs, enhancing user experience and boosting app engagement. Since 2014, Nazar has proven positive results with every client, including improving team development speed and driving business growth.
Portfolio
Experience
- Xcode - 11 years
- Software Development - 11 years
- Concurrency - 10 years
- UIKit - 8 years
- Swift - 8 years
- Push Notifications - 8 years
- SwiftUI - 5 years
- Artificial Intelligence (AI) - 2 years
Preferred Environment
Slack, Xcode, Jira, Firebase, AWS Command Line Interface (CLI), Vercel, Amazon S3 (AWS S3), ARKit, APIs, iOS SDK
The most amazing...
...thing I've done is lead the development of complex features for a HIPAA-compliant healthcare app.
Work Experience
Senior iOS Engineer
Shader
- Implemented efficient routing, persistence, and network layers, improving app performance for 100,000+ daily active users.
- Designed and implemented AI image generation and media management, including advanced gallery features and AR mask generation.
- Contributed to back-end and UI/UX decisions, ensuring seamless cross-functional alignment.
- Improved engagement by 15% by developing and launching paid subscriptions, push notifications functionality, and deep linking.
Senior Software Engineer
Sidequest Inc.
- Developed a SwiftUI app with media ARKit recording, deep linking, AI features, and a social video feed, aligning with principles and guidelines.
- Designed a scalable database and integrated Amazon S3 for media storage, enabling efficient real-time data handling and uploads.
- Built an API with authentication, CRUD, AI-driven endpoints, deep linking, and push notifications, ensuring reliability.
- Increased engagement by 25% by optimizing networking and caching for smoother interactions.
- Led product development from concept to MVP, ensuring alignment with business objectives and user satisfaction.
Lead iOS Engineer
Datasya
- Published and developed a complete VIPER SwiftUI app from scratch, achieving a 99.5% crash-free session rate.
- Implemented Core ML and TensorFlow computer vision models, reducing response time from 300 to 40 milliseconds for anonymization and screen capture.
- Developed media management tools, real-time video processing, AR video calling features, and passwordless authentication using AWS.
- Led the iOS team, hired new developers, and created a comprehensive development roadmap, improving development speed by 40%.
- Established cross-functional collaboration with designers, managers, and back-end engineers, ensuring alignment with business values.
- Implemented a CI/CD pipeline, conducting pull requests, code reviews, and unit and UI testing.
Senior iOS Engineer
Adozi Inc.
- Modularized the app architecture, saving 20% on development time and improving performance by 20% per report.
- Led collaboration with design and back-end teams for new and legacy feature development, ensuring scalability and reliability.
- Built end-to-end user flows for lesson booking, ensuring high usability.
- Developed a scalable checkout flow for lesson booking, ensuring seamless transactions and improved UX.
- Established CI/CD pipelines with Fastlane and Jenkins, automating deployments and reducing regression testing by four hours per release.
- Managed the iOS development team, increasing the team's performance by 50%.
Senior iOS Engineer
ARUM Trade LTD
- Architected and developed a trading app for iOS, enabling desktop-level trading functionality on mobile platforms.
- Implemented complex features like KYC and real-time trade tracking via WebSockets.
- Mentored developers, fostering skill growth and delivering key app features collaboratively.
Senior Mobile Engineer
Stack (by Appodeal)
- Ran A/B tests for 80+ ad networks, integrating and optimizing them for iOS and SDKs, improving revenue by 30%.
- Managed the development of a scalable internal analytics product with over 10 million requests per minute.
- Contributed to the Objective-C iOS SDK development and was later involved in Swift iOS SDK development.
- Maintained and developed new features for multiple large-scale iOS apps and integrated trust and safety features.
- Led the development of 20+ frameworks for several platforms, generating 80% of the company's revenue.
Experience
SeaGreen Healthcare Chat App
https://apps.apple.com/pl/app/seagreen/id1668005526/Education
Master's Degree in Computer Science
Lutsk National Technical University - Lutsk, Ukraine
Skills
Libraries/APIs
Xcode Server, Core Graphics, Core Animation, Firebase iOS SDK, AWS Amplify, Claude API, AVKit, React, Node.js, Stripe API, OpenCV
Tools
Slack, Xcode, Jira, Postman, Crashlytics, Android Studio, Apple Push Notifications, Claude Code, Jenkins, AWS Command Line Interface (CLI), Notion, CallKit, Claude, Claude Agent SDK, Expo
Languages
Swift, GraphQL, TypeScript, Kotlin, C#, Python, Objective-C
Frameworks
SwiftUI, UIKit, ARKit, Core Data, Combine, Core ML, Flux, Metal, Core Foundation, Unity, Flutter, React Native, Core Location, TensorFlow Lite, Apple Vision Framework, Unreal Engine, iOS SDK, gRPC
Paradigms
REST, Mobile Development, App Development, Automation
Platforms
Firebase, Visual Studio Code (VS Code), iOS, Vercel, Amazon Web Services (AWS), Apple Watch, MacOS, Docker
Storage
Amazon S3 (AWS S3), Google Cloud, PostgreSQL
Other
Software Development, Concurrency, APIs, GitHub Actions, AVFoundation, Crash Fixing, Pipelines, QA Process, WebSockets, MVVM-C, Push Notifications, Deep Linking, Google+ Authentication, Mobile App Development, Mobile Apps, SDKs, Content Delivery Networks (CDN), AI Agents, Scripting, App Store, Generative Systems, Artificial Intelligence (AI), OpenAI, Gemini, Supabase, Amplitude, VoIP, Payment APIs, Computer Vision, Machine Learning, Cursor AI, Healthtech, Wearables, TrueDepth Camera, Facial Tracking, Biometrics, Solana, Web UI
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