Vytautas is available for hire
Hire VytautasVytautas Saulis
Verified Expert in Engineering
Full-stack Developer
Vilnius, Vilnius County, Lithuania
Toptal member since February 14, 2022
Bio
Vytautas is a product engineer with 10+ years of experience building mobile apps, backends, payments and AI features. His focus now is AI: features and agents inside real products. He holds a Master's degree in Software Engineering from Vilnius University and has built for Locket, Luminor Bank, Ethos, Checkmate.com and Texture Capital. He has also delivered API security, cloud cost reduction and Stripe and Paysera payments, as the one senior person who owns a product from idea to release.
Portfolio
Sudorandom Labs Inc.
Expo.io, React Native, Web3, iOS, NestJS, Android, TypeORM
Locket Labs, Inc
React Native, TypeScript, Firebase, Java, Kotlin
Checkmate.com Inc.
React, React Native, TypeScript, Redux, Emotion Library, React Router...
Experience
- Node.js - 10 years
- Full-stack - 10 years
- React - 10 years
- React Native - 10 years
- NestJS - 5 years
- Artificial Intelligence (AI) - 2 years
- AI Agents - 2 years
- Claude Code - 1 year
Work Experience
React Native Developer
2025 - 2025
Sudorandom Labs Inc.
- Implemented deposit functionality, allowing users to fund accounts directly within the app. Integrated with back-end transaction APIs and handled error states, confirmations, and balance updates.
- Added support for theming, multi-language translation, and monitoring. Enabled runtime theme switching, integrated i18n workflows, and connected monitoring tools for tracking performance and errors.
- Rebuilt the application UI with a new design system. Replaced all existing components, updated navigation structure, and aligned styling with the new design specifications.
- Integrated on-ramp and off-ramp flows using Sphere and Bridge APIs. Connected external services for fiat-to-crypto and crypto-to-fiat transactions, including KYC handling and transaction tracking.
- Created a proxy backend using NestJS to support third-party provider connections via Privy. Handled authentication flows, request routing, and data transformation between services.
Technologies: Expo.io, React Native, Web3, iOS, NestJS, Android, TypeORM
React Native Developer
2025 - 2025
Locket Labs, Inc
- Implemented video recording functionality using React Native Vision Camera, enabling in-app video capture for over five million users. Integrated native camera APIs and managed runtime permissions to ensure broad device compatibility.
- Implemented camera roll access with integrated cropping, allowing users to select and edit media within the app. Connected to the device media library and implemented a cropping interface consistent with application workflows.
- Improved camera initialization time from 1.2 seconds to 300 milliseconds by optimizing rendering processes and camera module configuration. Identified and removed performance bottlenecks by refactoring rendering logic and camera lifecycle management.
- Implemented ultra-wide camera zoom functionality to support additional lens configurations across supported devices. Detected device capabilities at runtime and adjusted camera parameters to enable dynamic lens switching.
- Delivered core camera features in a production React Native application using Expo and React Native Vision Camera, supporting a user base of over five million.
Technologies: React Native, TypeScript, Firebase, Java, Kotlin
React Senior Developer
2024 - 2025
Checkmate.com Inc.
- Built an interactive pizza builder for both mobile and web applications.
- Maintained 20+ branded React websites from a single shared codebase.
- Maintained 20+ branded React Native apps from a single shared codebase.
- Set up CI/CD pipelines for the React Native apps with Fastlane.
- Integrated Freedom Pay across the mobile and web applications.
- Added Apple Pay and Google Pay to the ordering flow on mobile.
- Delivered ADA compliance and accessibility fixes on the React websites.
- Improved load times for large menus with more than 300 items.
Technologies: React, React Native, TypeScript, Redux, Emotion Library, React Router, React Navigation, Google Maps, Apple Pay, Google Pay, CircleCI, Sentry
Senior React Native Developer
2022 - 2023
Ondato
- Built a React Native SDK that lets mobile apps add Ondato identity verification.
- Implemented biometric authentication in the SDK with FaceTec.
- Wrote the developer documentation and support material for the SDK.
- Led a team of three on the SDK repository: goals, code reviews and delivery.
Technologies: TypeScript, React Native, React Navigation, Styled-components, SDKs, Figma, Redux, Redux Thunk, React, React Redux, React Query, APIs, Jira, Slack, Android, iOS, Swift, Kotlin, Firebase, Jest, FaceTec, Front-end
Senior Front-end Developer
2019 - 2023
Atobi
- Delivered features for a retail platform built with React Native and Next.js.
- Worked in an Agile team alongside design, development and QA.
- Improved coding standards and review practices across the codebase.
- Helped take the product from early stage to a production SaaS platform.
Technologies: TypeScript, React Native, Expo, React Query, React, Jest, Jira, Slack, Expo.io, Tailwind CSS, iOS, Android, Azure, Node.js, Figma, CI/CD Pipelines, Redux, React Redux, JavaScript, Agile, CSS, HTML, HTML5, SCSS, Firebase, Sentry, Front-end, Next.js, WYSIWYG Web Builders
Senior Full-stack Developer
2020 - 2021
Nano Bitas
- Built a microservices architecture with domain-driven design to replace a monolith.
- Led the migration of a legacy system to a modern C# codebase.
- Managed a team of two developers through mentoring and code reviews.
- Set up an automated CI/CD pipeline for deployments to production.
Technologies: C#, TypeScript, Redux, Redux Thunk, React, Agile, React Redux, React Query, APIs, Jira, Full-stack Development, Full-stack, Back-end, Slack, Jest, C#.NET, .NET, .NET Core, AutoMapper, Domain-driven Design (DDD)
Senior React Developer
2020 - 2021
Luminor
- Built a React component library in TypeScript for the bank's internal applications.
- Focused on performance and responsive behavior across all components.
- Made the components modular and configurable so teams could adapt them.
- Wrote the library documentation to help developers adopt the components.
Technologies: TypeScript, React, Jest, Jira, Slack, HTML, CSS, SCSS, JavaScript, React Redux, Redux, Styled-components, Front-end
Senior React Native Developer
2019 - 2020
AAG Ventures
- Built MetaOne, a cross-platform React Native application for iOS and Android.
- Added task management and collaboration features to the application.
- Implemented security and data privacy measures across the application.
- Planned the development schedule and coordinated delivery with the team.
Technologies: React Native, Android, iOS, Jest, TypeScript, Figma, Jira, MetaMask, Slack, Agile, Redux, React, React Redux, React Query, Firebase, Sentry, Web3, Front-end
Senior Full-stack Developer
2018 - 2020
L'Officiel
- Owned development of the React Native app, React back office and Symfony API.
- Implemented real-time communication between the app and the API.
- Improved the performance of both the mobile app and the API.
- Implemented security measures to protect user and business data.
- Wrote the project documentation and provided support for the team.
- Worked with the business to improve app adoption and user engagement.
Technologies: PHP, JavaScript, TypeScript, Firebase, Jira, AWS Command Line Interface (CLI), Symfony, React Native, iOS, Android, React, React Redux, Styled-components, Redux, React Query, Figma, HTML, CSS, Agile, Full-stack, Front-end, Back-end, Full-stack Development, SQL, MySQL, Startups, eCommerce
Full-stack Software Developer
2017 - 2018
Amerant Bank
- Developed ASP.NET web applications for the bank using C# and .NET.
- Worked in an Agile team and contributed to process improvements.
- Improved application performance for a better user experience.
Technologies: C#, .NET, ASP.NET, JavaScript, Agile, CSS, SCSS, HTML, HTML5, Front-end, Back-end
Project History
Noktis AI Sleep App
https://noktis.appAI sleep app and my own product, built as one engineer: the app, API, web funnel and admin panel. It uses Claude to build a personal three-track sound bundle for each subscriber every evening. Subscriptions run on Stripe and RevenueCat, and it's live on the App Store and Google Play.
Matter AI Nutrition App
https://matterformula.comAI nutrition and meal ordering app, built from the start with the founder. I owned the whole React Native app, including the AI nutritionist, food logging, meal ordering, Braze and Firebase push notifications and Fastlane CI/CD, and worked on the backend API as well. The app is rated 4.8 on the App Store.
Ivio Invoicing App
Invoicing and tax app in development for self-employed people in Lithuania, and my own product. Users will create invoices by voice, photo or text and see tax forecasts. I built the first version of the API in 11 days with AI-assisted engineering.
Timespex Booking Platform
https://timespex.comSenior engineer on a booking platform. I built API access control, rate limiting and login protection, and reduced cloud costs by consolidating load balancers and moving development to a smaller server. I replaced the retired traffic router, made queued jobs and search survive server replacements, built Paysera payments and improved the Stripe flows.
Ethos Annuities Flow
https://ethos.comAnnuities work for an insurance company. I oversaw and built the annuities landing page, its experiments and the Optimizely and Segment setup. I built an annuities flow with four A/B tested variants to find which brought the most qualified leads, integrated Salesforce and added logging that cut lead debugging from hours to minutes.
Ines4U Emergency Support App
Emergency support web application used by healthcare professionals. I built multi-step medical assessment forms, trauma scoring and clinical decision support, tablet and mobile layouts for use during emergency response with offline-resilient forms, and patient data validation based on standard clinical protocols.
DonateMate Donations App
https://donate-mate.comDonations app for the US market. I was the sole owner of the frontend and led the React Native app through to release on the App Store and Google Play. I built donation tracking, goals, social activity, search and multi-criteria filtering, and added Stripe payments and real-time analytics.
Texture Capital Validator Interface
https://texture.capitalDigital asset platform. I built the wallet validator interface for a Canton distributed ledger platform, owned authentication with Keycloak, including tokens, sessions and role-based access, and built a typed smart contract layer over Canton's JSON API.
Clarity Bookkeeping App
B2B bookkeeping app for wholesale operators. As technical lead for non-technical founders, I led architecture and estimates, built an offline-first React Native app with local storage and a NestJS API, and checked each delivery against the approved plan, line by line.
Auralyo Focus Audio App
https://www.auralyo.comFocus audio app for deep work, study and creative flow. I built the iOS and Android app and the NestJS API behind personal focus audio sessions, added background audio, focus tracking and streaks across six work modes, and set up subscriptions with RevenueCat and releases to the App Store and Google Play.
Circles
Circles is a React Native mobile app that provides online support for people. My main goal was to build new features for the app, and I also redesigned screens, wrote end-to-end tests and fixed bugs, working in an agile team on iOS and Android with Firebase.
The Poolit
The Poolit is a React Native mobile app for investments. I tested all the code I delivered with Jest, introduced TypeScript best practices for React Navigation, used lint to keep dependencies sorted, and suggested changes to the team's code review process.
Education
2019 - 2023
Master's Degree in Software Engineering
Vilnius University - Vilnius, Lithuania
2015 - 2019
Bachelor's Degree in Software Engineering
Vilnius University - Vilnius, Lithuania
Skills
Libraries/APIs
React, Node.js, React Navigation, React Redux, React Query, AutoMapper, MobX, Stripe, Claude API, Emotion Library, React Router, Google Maps
Tools
Expo, Jira, Figma, Slack, Expo.io, Redux Thunk, OneSignal, Claude Code, Sentry, MetaMask, AWS Command Line Interface (CLI), ChatGPT, CircleCI, Fastlane, Braze, Optimizely, Keycloak, TestFlight
Languages
C#, JavaScript, PHP, TypeScript, CSS, HTML5, HTML, SCSS, ECMAScript (ES6), SQL, Swift, Kotlin, C#.NET, Java
Frameworks
Angular, React Native, Redux, .NET Core, Jest, ASP.NET, Tailwind CSS, NestJS, Symfony, Laravel, Material UI, Next.js, .NET, i18next
Paradigms
Clean Code, Agile, Mobile Development
Platforms
iOS, Android, Amazon Web Services (AWS), Firebase, Kubernetes, Azure, Blockchain, Salesforce, PostHog, MacOS
Storage
Database Architecture, MySQL, Microsoft SQL Server, MongoDB, PostgreSQL, SQLite
Other
Styled-components, Software, Engineering Software, Full-stack, Architecture, APIs, Front-end, Back-end, Full-stack Development, DOM, i18n, eCommerce, Software Development, Data Visualization, Charts, Data Structures, CI/CD Pipelines, SDKs, FaceTec, Web3, Startups, WYSIWYG Web Builders, Artificial Intelligence (AI), AI Agents, Domain-driven Design (DDD), OpenAI GPT-4 API, OpenAI GPT-3 API, Apple Pay, Google Pay, TypeORM, A/B Testing, Segment, WatermelonDB, EAS
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