Herman is available for hire
Hire HermanHerman Kononets
Verified Expert in Engineering
Mobile Developer
Fairfax, VA, United States
Toptal member since March 11, 2026
Bio
Herman is a senior mobile developer specializing in Android and iOS with extensive experience building secure, scalable, and high-performance applications. He is an expert in modern mobile architectures, BLE integrations, and encryption systems. Herman crafts reliable products with clean architecture and excellent user experience, delivering solutions that meet both technical and business goals.
Portfolio
Washos
Swift, Xcode, SwiftUI, UIKit, Objective-C, Alamofire, Core Data, Firebase...
Luminary Bank
Swift, Kotlin, SwiftUI, UIKit, Android Jetpack, Jetpack Compose, RoomDB...
IPG
Swift, SwiftUI, Kotlin, Jetpack Compose, Android, iOS, Retrofit 2, KOIN, OkHttp...
Experience
- Swift - 6 years
- Firebase - 6 years
- Kotlin - 6 years
- Android Jetpack - 5 years
- Clean Architecture - 5 years
- UIKit - 5 years
- Model View ViewModel (MVVM) - 4 years
- SwiftUI - 3 years
Preferred Environment
Android Studio, Xcode, MacOS, Mobile, Push Notifications, Jira, GitHub, Kotlin Multiplatform, OpenCV, Laravel, PHP
The most amazing...
...work I've done is lead the build of a secure BLE-based mobile system for smart intercom devices, implementing encrypted communication and scalable architecture.
Work Experience
Senior iOS Developer
2024 - PRESENT
Washos
- Developed an iOS client for a mobile car detailing booking platform, enabling customers to schedule, manage, and track detailing services directly from their smartphones.
- Implemented a scalable booking workflow with real-time availability, reducing scheduling conflicts and improving booking completion rates.
- Integrated secure payment processing and order management features, allowing users to book and pay for detailing services in under 60 seconds.
- Designed and optimized a user-friendly interface using Swift and modern iOS frameworks, improving customer engagement and reducing drop-off during the booking flow.
- Collaborated with back-end engineers and product stakeholders to define API contracts and ensure reliable synchronization between mobile clients and service providers.
- Improved app performance and stability by optimizing network requests, caching strategies, and error handling across booking and order-management flows.
- Delivered production-ready features through Agile iterations, contributing to faster feature releases and continuous product improvements.
Technologies: Swift, Xcode, SwiftUI, UIKit, Objective-C, Alamofire, Core Data, Firebase, Model View ViewModel (MVVM), Unit Testing, Figma, Keychain, Google Maps SDK, RESTFul APIs, Core Location, Stripe, Apple Pay, Crashlytics, Analytics, SOLID Principles, iOS, iOS SDK, Android, Mobile Apps, Stripe API, Mobile Development, Mobile App Development, App Store, Architecture, Location Services, Maps, Mobile, Payment APIs, Push Notifications, GitHub, Google Play Store, App Store Connect, TestFlight, Software Architecture, Minimum Viable Product (MVP), Jetpack Compose, Coroutines, Google Maps API, Automated UI Testing, iOS Native Libraries, REST APIs, JSON, Performance Optimization, iOS App Development, API Integration, Mobile Architecture, Subscriptions, StoreKit 2, Claude Code, Mixpanel, User Interface (UI), User Experience (UX), Artificial Intelligence (AI), AI Tools, App Design, Authentication, Claude, APIs
Senior Mobile Developer
2022 - 2024
Luminary Bank
- Architected and developed iOS and Android mobile banking applications from scratch using Swift and Kotlin, delivering a secure and scalable client for daily banking operations.
- Implemented secure authentication flows, including biometric login and token-based authorization, improving user security and reducing login friction.
- Designed and integrated core banking features, including account management, transaction history, transfers, and payment services.
- Built a modular mobile architecture with clean separation of data, domain, and presentation layers, enabling faster feature development and long-term maintainability.
- Integrated RESTful APIs with robust error handling, encryption, and secure data storage to meet financial security and compliance requirements.
- Optimized application performance and network efficiency, reducing loading times for account and transaction data.
- Collaborated with back-end engineers, QA teams, and product stakeholders to deliver secure and reliable banking features through iterative Agile releases.
Technologies: Swift, Kotlin, SwiftUI, UIKit, Android Jetpack, Jetpack Compose, RoomDB, Core Data, RESTFul APIs, WebSockets, Encryption, Keychain, Core Location, Two-factor Authentication (2FA), Model View ViewModel (MVVM), Clean Architecture, Kanban, Figma, SOLID Principles, iOS, iOS SDK, Android, Mobile Apps, Mobile Development, Twilio API, Mobile App Development, App Store, Architecture, Messaging, Mobile, Push Notifications, Real-time Systems, Jira, GitHub, Google Play Store, App Store Connect, TestFlight, Software Architecture, Minimum Viable Product (MVP), Coroutines, Java, Android SDK, Automated UI Testing, iOS Native Libraries, REST APIs, JSON, Application Architecture, Performance Optimization, Android Development, iOS App Development, Amazon Web Services (AWS), API Integration, Mobile Architecture, User Interface (UI), Pixel Perfect, User Experience (UX), App Design, Authentication, APIs, Google Cloud Platform (GCP)
Senior Mobile Developer
2021 - 2024
IPG
- Developed and maintained a global co-working desk booking app, implementing search, booking flows, and real-time availability, improving user conversion and engagement.
- Integrated maps, location services, and third-party APIs to enable seamless discovery of co-working spaces worldwide, reducing booking friction and enhancing user experience.
- Optimized app performance and architecture, reducing crash rates and improving load times, while collaborating with cross-functional teams to deliver scalable features.
Technologies: Swift, SwiftUI, Kotlin, Jetpack Compose, Android, iOS, Retrofit 2, KOIN, OkHttp, Alamofire, Microsoft Authentication Library (MSAL), Firebase, Java, Android SDK, Automated UI Testing, Model View Intent (MVI), iOS Native Libraries, REST APIs, JSON, Application Architecture, Performance Optimization, Android Development, iOS App Development, API Integration, Content Delivery Networks (CDN), Mobile Architecture, User Interface (UI), User Experience (UX), App Design, Authentication, APIs, Google Cloud Platform (GCP), React Native
Senior Mobile Developer
2018 - 2021
Liza Remote Control
- Developed a companion mobile app for smart home remote control devices, implementing device configuration, drag-and-drop UI for control mapping, and seamless synchronization between smartphone and hardware.
- Built and optimized connectivity with Wi-Fi and infrared-based devices (TVs, Philips Hue, Sonos, and Spotify), enabling centralized control of home automation services through a unified mobile interface.
- Designed and improved intuitive user flows for multi-user personalization and local (no-cloud) data handling, enhancing privacy, usability, and reliability of device interactions.
Technologies: Swift, UIKit, Android, iOS, Retrofit 2, Alamofire, Core Bluetooth, Bluetooth, RESTFul APIs, Java, Android SDK, Automated UI Testing, Model View Intent (MVI), Apple HealthKit, WatchOS, AVFoundation, iOS Native Libraries, REST APIs, JSON, Performance Optimization, Android Development, Kotlin Multiplatform Mobile (KMM), iOS App Development, Android NDK, API Integration, Audio Engines, Content Delivery Networks (CDN), Mobile Architecture, Subscriptions, Text-to-Speech (TTS), User Interface (UI), User Experience (UX), App Design, Android TV, APIs, Google Cloud Platform (GCP)
Senior Mobile Developer
2015 - 2018
Trionika
- Developed and optimized mobile applications for high-traffic, content-driven platforms, contributing to scalable user acquisition systems and improving performance across SEO-driven products.
- Implemented integrations with back-end services and analytics systems, enabling data-driven feature development and supporting traffic growth and monetization strategies.
- Improved app architecture and performance (networking, caching, and stability), reducing load times and increasing user engagement in products focused on large-scale traffic and content delivery.
Technologies: Swift, Kotlin, Java, iOS, Android, Firebase, RESTFul APIs, WebSockets, Twilio API, WebRTC, SIP, Clean Architecture, Model View ViewModel (MVVM), Google Maps API, Android SDK, Automated UI Testing, Model View Intent (MVI), Apple HealthKit, WatchOS, AVFoundation, iOS Native Libraries, REST APIs, JSON, Application Architecture, Performance Optimization, Kotlin Multiplatform Mobile (KMM), iOS App Development, Android NDK, Python, Amazon Web Services (AWS), API Integration, Audio Engines, Content Delivery Networks (CDN), Mobile Architecture, Subscriptions, Text-to-Speech (TTS), StoreKit 2, Laravel, PHP, User Interface (UI), Pixel Perfect, User Experience (UX), App Design, APIs, Flutter, React Native
Experience
Luminary
https://luminarybank.com/I contributed to the development of a mobile banking client for Luminary Bank, a digital financial platform focused on global payments and modern fintech services. The application enables users to manage multi-currency accounts, send and receive international payments, and convert between crypto and fiat assets within a secure mobile environment.
As a mobile developer, I participated in building both iOS and Android applications from the ground up, implementing core banking functionality, including authentication, account management, transaction history, and payment processing. I collaborated closely with back-end engineers and product teams to design scalable mobile architecture, integrate secure APIs, and deliver a reliable, high-performance banking experience focused on usability and financial data security.
As a mobile developer, I participated in building both iOS and Android applications from the ground up, implementing core banking functionality, including authentication, account management, transaction history, and payment processing. I collaborated closely with back-end engineers and product teams to design scalable mobile architecture, integrate secure APIs, and deliver a reliable, high-performance banking experience focused on usability and financial data security.
Washos
https://www.washos.com/I worked on the development of the mobile client for Washos, an on-demand platform that lets customers book professional car-washing and detailing services directly from their smartphones. The service connects users with vetted technicians who travel to the customer’s location to perform vehicle cleaning and detailing, often within the same day.
As an iOS developer on the project, I contributed to building key features of the booking and service-management experience, including appointment scheduling, service selection, location handling, payment processing, and real-time booking updates. I collaborated with back-end engineers and product teams to integrate APIs, improve performance, and deliver a reliable and user-friendly mobile experience that streamlined the entire car-detailing booking workflow.
As an iOS developer on the project, I contributed to building key features of the booking and service-management experience, including appointment scheduling, service selection, location handling, payment processing, and real-time booking updates. I collaborated with back-end engineers and product teams to integrate APIs, improve performance, and deliver a reliable and user-friendly mobile experience that streamlined the entire car-detailing booking workflow.
Together Desk Booking
https://apps.apple.com/us/app/together-desk-booking/id1563045637The Together app is designed to get office workers back together! Using uploaded floor maps and configurable naming for desks and floors, it can be customized as needed to fit right into your corporate culture. Parking availability, along with a robust vaccine and test documentation workflow, will enable a safe return.
Education
2010 - 2015
Master's Degree in Software Engineering
NTUU Kyiv Polytechnic Institute - Kyiv, Ukraine
Skills
Libraries/APIs
Stripe, Google Maps API, iOS Native Libraries, REST APIs, Stripe API, Twilio API, Alamofire, Google Maps SDK, Retrofit 2, Microsoft Authentication Library (MSAL), WebRTC, OpenCV
Tools
Xcode, Android Jetpack, Jira, GitHub, TestFlight, Apple HealthKit, Claude Code, Claude, Android NDK, Algorithm Design, Android Studio, Figma, Crashlytics
Languages
Swift, Objective-C, Kotlin, Java, SQL, Python, PHP
Frameworks
SwiftUI, UIKit, iOS SDK, Android SDK, StoreKit 2, Laravel, Flutter, React Native, Core Data, Core Location, KOIN, Core Bluetooth
Paradigms
Unit Testing, Model View ViewModel (MVVM), Mobile Development, Model View Intent (MVI), Application Architecture, Real-time Systems, Agile, Scrum, Kanban, Test-driven Development (TDD), Clean Architecture
Platforms
Firebase, iOS, Android, Mobile, WatchOS, Google Cloud Platform (GCP), MacOS, Amazon Web Services (AWS), Mixpanel, Android TV, Keychain
Storage
JSON, NoSQL, RoomDB
Other
RESTFul APIs, Apple Pay, Jetpack Compose, Mobile Apps, Mobile App Development, App Store, Architecture, Location Services, Maps, Push Notifications, Google Play Store, App Store Connect, Software Architecture, Kotlin Multiplatform, Minimum Viable Product (MVP), Coroutines, Automated UI Testing, AVFoundation, Performance Optimization, Android Development, Kotlin Multiplatform Mobile (KMM), iOS App Development, API Integration, Audio Engines, Content Delivery Networks (CDN), Mobile Architecture, Subscriptions, Text-to-Speech (TTS), User Interface (UI), Pixel Perfect, User Experience (UX), App Design, Authentication, APIs, OOP Designs, Messaging, Payment APIs, Artificial Intelligence (AI), AI Tools, Pattern Design, SOLID Principles, Data Structures, Cryptography, Technical Documentation, Analytics, WebSockets, Encryption, Two-factor Authentication (2FA), OkHttp, Bluetooth, SIP, DI
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