Hello! I am David Kuczynski
ABOUT ME
Senior Software Engineer — Full Stack · Mobile · AI with 10+ years of experience designing, building, and shipping production software across mobile, web, backend, and AI. I have delivered 50+ applications for dating, social, wellness, fitness, e-commerce, and real-estate products, from native iOS (Swift) and Android (Kotlin) and cross-platform React Native to React/Next.js frontends and Node.js, Laravel, Django, and Spring backends on AWS.
I build AI-powered product features with LLM APIs, retrieval-augmented generation, on-device machine learning, and speech technology, and use AI-assisted engineering workflows to ship faster. Strong in MVVM and Clean Architecture, real-time systems (WebSocket, WebRTC, LiveKit), Agile, and TDD.
Services I offer
AI Product Development
LLM-powered features built on OpenAI and Claude: chatbots, in-app assistants, RAG over your own data, content moderation, and document automation.
Mobile App Development
Native iOS (Swift, SwiftUI) and Android (Kotlin, Compose) or cross-platform React Native apps, taken from architecture to App Store and Google Play launch.
Full Stack Web Development
React and Next.js frontends backed by Node.js, Laravel, or Django APIs, with secure payments, subscriptions, and clean, well-tested code.
Real-time & Cloud Systems
Video calling, chat, and live updates with LiveKit, WebRTC, and WebSocket, deployed on AWS with Docker, CI/CD, and monitoring for reliability.
My Experience
Senior Software Engineer (Mobile & AI)
April 2022 ~ February 2026Global Personals LLC, United States
- Led development of the Tinder-style dating apps Fling and Highreply on React Native for iOS and Android, with a focus on engagement, retention, and a smooth user experience.
- Built AI-powered engagement features on LLM APIs (OpenAI, Claude), including personalized conversation starters and profile bio suggestions, to increase replies and match activity.
- Implemented AI-driven safety and content moderation for photos and chat messages (image classification and toxic-text detection), cutting manual review and improving member trust.
- Improved matchmaking quality by feeding user rating and behavioural signals into ML-based recommendation ranking.
- Integrated low-latency 1:1 video chat using the LiveKit SDK, plus scalable WebSocket-based real-time messaging and notifications.
- Implemented in-app purchases and subscriptions to support monetization, and Firebase Cloud Messaging push notifications to re-engage users.
- Used React Query for efficient data fetching, caching, and server-state management.
- Introduced AI-assisted development workflows (Claude Code, Cursor) to speed up delivery, automate refactors and tests, and raise code quality across the team.
Full Stack & AI Engineer
September 2021 ~ May 2025Toptal Inc, United States
- Selected into Toptal’s exclusive network of top freelance engineers to deliver full stack solutions for global clients.
- Designed and developed 10+ scalable web and 10+ mobile applications using modern technologies.
- Built LLM-powered features for client products, including customer-support chatbots and in-app AI assistants, using the OpenAI and Claude APIs.
- Implemented retrieval-augmented generation (RAG) pipelines with LangChain and vector search (pgvector, Pinecone) so assistants answer from each client’s own documents and data.
- Automated document processing and data extraction workflows with LLMs, replacing manual data entry for client operations teams.
- Built Rubicon, a Telegram bot that delivers real-time crypto trading signals from whale wallet tracking, using the Cielo SDK to monitor large wallets across multiple chains and alert users to swaps, transfers, and new token buys within seconds.
- Designed the bot’s event pipeline (Cielo feed and webhooks, signal filtering and deduplication, Telegram Bot API delivery) with per-user watchlists, alert thresholds, and inline-keyboard commands.
- Partnered with product and design teams to ship user-focused features, building secure, reliable APIs and improving performance through optimization and refactoring.
Senior Mobile Engineer
March 2024 ~ February 2025AlchemistOne, Canada
- Owned end-to-end delivery of native iOS (Swift, SwiftUI) and Android (Kotlin, Jetpack Compose) mindfulness and recovery apps, from technical design through App Store and Google Play launch.
- Defined the mobile architecture on MVVM and Clean Architecture with clear domain, data, and presentation layers, making features faster to build and easier to test.
- Engineered privacy-first features with encrypted local storage (Keychain, Android Keystore) and minimal data collection for sensitive health and recovery information.
- Built immersive media playback (guided audio, video, ambient soundscapes) with background audio, offline downloads, and seamless session resume.
- Profiled and optimized startup time, memory use, and rendering to deliver a smooth, responsive experience on low-end devices.
- Established unit and UI test coverage (XCTest, JUnit, Espresso) and automated builds and releases with CI/CD and Fastlane.
Full Stack Mobile Engineer
October 2021 ~ March 2022Vivid Unity Games, United Kingdom
- Architected and built a cross-platform React Native social gaming app for iOS and Android from a shared TypeScript codebase.
- Designed scalable Node.js and Express backend services with event-driven architecture, background job automation, and Redis caching.
- Delivered 1:1 and group audio and video calling with the LiveKit SDK (WebRTC), including connection-quality handling and reconnection logic.
- Built a WebSocket real-time messaging system for direct and group chats, presence, typing indicators, and live in-game event updates.
- Containerized services with Docker and deployed them on AWS, adding monitoring and logging for production reliability.
Full Stack Engineer
November 2020 ~ August 2021MacroFit Inc, United States
- Engineered responsive fitness program and workout modules in React.js and TypeScript with reusable, component-driven UI.
- Built iOS and Android mobile apps for fitness tracking and guided workouts, integrating Apple HealthKit and Google Fit.
- Designed and documented versioned RESTful APIs in Laravel (PHP) and MySQL serving both the web and mobile clients.
- Established end-to-end test automation with Laravel Dusk and PHPUnit, catching regressions before release.
- Built the e-commerce storefront for fitness hardware with secure checkout via Stripe, PayPal, and Affirm financing, including webhooks and order management.
Front End Engineer, Agile Developer
March 2019 ~ October 2020Intelligent Voice Limited, London, United Kingdom
- Built a WebRTC video-conferencing MVP with real-time AI subtitles, streaming audio to NVIDIA Jarvis speech-to-text via Node.js and Socket.io and rendering live captions in React.
- Developed three AI-powered smart-transcript applications in React.js and TypeScript from complex Adobe XD designs, featuring synchronized playback, speaker labels, and searchable transcripts.
- Drove feature iterations from user research and feedback, raising user satisfaction from 81% to 95%.
- Created a Chrome extension that uses NLP to extract and display key topics and tags from YouTube videos.
- Extended the MynaRecorder desktop application (C# / .NET) with new features and resolved long-standing defects.
- Worked in two-week Agile sprints with code reviews and TDD, collaborating closely with data scientists and backend engineers.
Mobile Developer
April 2013 ~ October 2020Narmer Technology Inc, Regina, Canada
- Designed, developed, and published 35+ native iOS (Objective-C, Swift) and Android (Java, Kotlin) apps for clients in e-commerce, real estate, social media, and on-demand services.
- Led the migration of 10 iOS applications to Android, achieving full feature parity with platform-native UX and performance.
- Built backend APIs and admin panels (Node.js, PHP, Firebase) and integrated maps, geolocation, payments, push notifications, and social login.
- Managed the full release lifecycle (store submissions, review compliance, crash monitoring) and rapidly resolved client-reported issues to keep apps stable and highly rated.
- Mentored junior developers and set coding standards and code-review practices across the mobile team.
Bachelor's Degree in Computer Science
2008 ~ 2012Czech Technical University In Prague
Tech Stack
AI & ML
OpenAI API, Anthropic Claude API, LangChain, RAG, vector search (pgvector, Pinecone), prompt engineering, AI content moderation, Core ML, ML Kit, TensorFlow Lite, speech-to-text (NVIDIA Riva/Jarvis), Claude Code, Cursor, GitHub Copilot
Mobile
Swift, SwiftUI, Objective-C, iOS SDK, Kotlin, Jetpack Compose, Java, Android SDK, React Native, Expo, MVVM, Clean Architecture, In-App Purchases & Subscriptions
Frontend
React.js, Next.js, Vue.js, Angular, TypeScript, JavaScript, HTML5, CSS3, Tailwind CSS, Bootstrap, React Query
Backend
Node.js, Express.js, Laravel (PHP), Python / Django, Java Spring Boot, C# / .NET, Ruby on Rails, REST, GraphQL
Real-time
WebSocket, Socket.io, WebRTC, LiveKit, Firebase Cloud Messaging
Cloud & DevOps
AWS (Lambda, EC2, S3, CloudFront, Cognito, DynamoDB, SES, IoT, Chime), Firebase, Docker, CI/CD pipelines, Fastlane, Git
Databases
PostgreSQL, MySQL, MongoDB, Redis, DynamoDB, Firebase Firestore
Practices
Agile / Scrum, Test-Driven Development, end-to-end test automation, payments (Stripe, PayPal, Affirm), performance optimization
By the Numbers
What would you like to Do?
Hire me!My Works
Rubicon Bot
What clients & colleagues say
David was always a pleasure to work with, demonstrating strong technical skills, excellent communication, and a genuine team-oriented attitude. His ability to bridge front-end development with backend functionality made our collaboration efficient and productive. I highly recommend David to any organization looking for a talented, dependable, and collaborative application developer.
David was able to quickly understand our current systems and PERFECTLY integrated our Stripe/Node.js requirements. Very professional and easy to work with. Will definitely hire again.
David did a great job. I didn't have that much information for him to create about page and how it works but he still manages to create great content and very quickly also.
David has done a great job not only is he very talented on what he does but also good at communicating. I would give him more stars if I could but the system only allows five.