Karolis Stulgys
Verified Expert in Engineering
Marketplaces Developer
Vilnius, Vilnius County, Lithuania
Toptal member since March 8, 2022
Karolis is an AI product engineer with 7 years of experience in building web products. As the 1st engineer at PEXX, he established the architecture and developed the front end and APIs. Karolis also recruited and led an initial team of 5 engineers, successfully launching the platform 2 weeks ahead of schedule. He specializes in React, Next.js, and TypeScript, and utilizes coding agents like Claude and GPT. His previous clients include Trustpilot, Irish Life, An Post, and RNHB.
Portfolio
Experience
- Bug Fixes - 7 years
- Web - 7 years
- Communication - 7 years
- Development - 7 years
- React - 7 years
- Node.js - 7 years
- Debugging - 7 years
- Monorepos - 7 years
Work Experience
Software Engineer
Macaw
- Rebuilt the legacy website of RNHB, a Dutch real-estate financier, on Next.js and Contentful.
- Modeled the content in Contentful so the content team publishes without an engineering deploy.
- Automated most ticket triage, implementation, and pull requests with custom coding-agent skills.
Founding Engineer
PEXX
- Built pexx.com as engineer number one, a stablecoin payments and banking platform that moves USDT and USDC to fiat.
- Set the platform architecture and built the frontend and the APIs.
- Recruited and led the first team of five engineers. The launch shipped two weeks ahead of schedule.
Software Engineer
Bound
- Built a new mobile application for visionI in React Native, from an empty repository to release.
- Built the companion web application in Next.js and TypeScript.
- Shipped both clients inside a three-month contract.
Front-end Developer
Apart People AS
- Built front-end UI components in React and shadcn/ui for a real-estate product.
- Integrated back-end APIs in Next.js and TypeScript, with Supabase for data and auth.
- Planned and implemented application features with Claude Code as the coding agent.
Front-end Developer
All human
- Built the first design system for Irish Life in React, working inside their UX team.
- Modernized legacy Irish Life front ends and moved them onto the new React design system.
- Redesigned core public-facing flows for An Post with a focus on accessibility.
Software Engineer
TrustPilot
- Built new front-end integrations in React for Shopify, Wix, and Mailchimp.
- Worked in a team of six developers with one product owner and one designer.
- Reviewed UI and UX designs with the designer to confirm technical feasibility.
Software Engineer
Rocket
- Moved a legacy enterprise desktop application onto a React web platform.
- Rebuilt the desktop workflows as web screens in React and TypeScript.
- Worked in an Agile team through the migration and on new feature delivery.
Front-end Engineer
Netfront
- Built responsive, pixel-accurate web UI in React and TypeScript.
- Shipped production feature work alongside designers and back-end engineers.
- Delivered client design projects in React and Redux against agency deadlines.
Front-end Engineer
UserCentric Pty Ltd
- Built mobile-first prototypes and MVPs in React for enterprise clients.
- Turned designer mockups into responsive interfaces for web and mobile.
- Worked directly with clients and designers on UI and UX requirements.
Project History
React Component Design System
Apps for eCommerce Platforms
POC Binary Options Trading App
Crypto Payment Gateway for USDC and USDT Stablecoin Payments
Create PDFs and Images from HTML in Seconds
https://tailwindpdf.comEducation
Master's Degree in Thermal Engineering (MSc), Building Engineering (BSc)
Vilnius Gediminas Technical University - Vilnius, Lithuania
Certifications
Full-stack Development
freeCodeCamp
Skills
Libraries/APIs
React, Node.js, Stripe API, React Testing Library, OpenAI API, TanStack Table, D3.js, Stripe, REST APIs, Typeform, API Development, Auth, React Router, Telegram Messenger API, WhatsApp API, Mapbox API, Intercom API, Shopify API, Zod, Playwright, Claude API, React Redux, CSSinJS
Tools
Git, Zoom, Adyen Payments, Figma to HTML, ChatGPT, Shadcn, Google Sheets, AI Prompts, GitHub, Terraform, Amazon CloudWatch, GitLab CI/CD, Claude Code, Claude, Whisper, Expo, JSON Schema, Shadcn UI, Webpack, Jira, Firebase Authentication, TestFlight, ComfyUI, Codex, Spreadsheets, Google Workspace, Astro, Prisma, Figma, Slack
Languages
TypeScript, JavaScript, CSS, HTML, GraphQL, HTML5, CSS3, Pine Script, Python, ECMAScript (ES6), Google Apps Script, SQL
Frameworks
Next.js, React Native, Tailwind CSS, Remix, Ant Design, Material UI, MUI CSS, Express.js, Fastify, Angular, Redux, NestJS, Payload CMS, LangGraph, Vanilla JS, Agentic Frameworks, Jest, Cypress, ORMLite, Chrome
Paradigms
Agile, Responsive Web Design (RWD), Search Engine Optimization (SEO), Unit Testing, UI Design, Agile Project Management, B2B, REST, Component-based Development, Microservices, Model Context Protocol (MCP), Mobile Development, Microfrontends, Automation, Web Application Architecture, DevOps, Azure DevOps, Clean Code, Testing, Continuous Integration (CI), Stress Testing, Role-based Access Control (RBAC), Conversion Rate Optimization (CRO), Application Architecture
Platforms
Visual Studio Code (VS Code), Firebase, Amazon Web Services (AWS), Vercel, Shopify, iOS, Android, Azure, HubSpot, Google Cloud Platform (GCP), Linux, Web, Harness, WordPress, WooCommerce, Azure Functions, Mobile, Vertex AI, Docker, Google AppSheet, Blockchain, MacOS, Typesafe, Contentful
Storage
PostgreSQL, Redis, Data Pipelines, Database Modeling, Data Integration, MongoDB, JSON, Databases, Google Cloud, ClickHouse, Database Architecture, SQLite, MySQL, Cloud Firestore
Industry Expertise
Web Design, Healthcare
Other
Responsive Design, APIs, Proof of Concept (POC), Artificial Intelligence (AI), Full-stack Development, Minimum Viable Product (MVP), API Integration, Front-end Development, Pixel Perfect, Responsiveness, Storybook, Front-end, Full-stack, Dashboards, Architecture, Technical Leadership, CI/CD Pipelines, Software Architecture, Gemini API, Image Generation, eCommerce, Content Management Systems (CMS), Headless CMS, Apple Pay, Integration, Large Language Models (LLMs), RESTFul APIs, React Hooks, UI Frameworks, Figma to React, Radix UI, Strapi, Web Development, Real Estate, Algorithms, Responsive UI, AI Integration, Affiliate Marketing API integration, Supabase, Supabase Auth, SaaS, Startups, Anthropic, Looker Studio, Web Scraping, Mobile eCommerce, Payment APIs, eCommerce Development, Server-side Rendering (SSR), Static Site Generators, Agentic AI, Prompt Engineering, Retrieval-augmented Generation (RAG), AI Architecture, AI Automation, Cloud, Image Processing, Fintech, Mobile Apps, Payments, Data Visualization, AI Tools, AI Agents, Event-driven Systems, AI-assisted Development, AI-generated Code, Web App Development, Lovable, OAuth, Webex, Product Lifecycle Management (PLM), SDKs, Intercom, Webhooks, Azure Data Lake, Financial Data, Accounting Systems, Data Modeling, Database Normalization, System Integration, Zustand, Application State Management, Apify SDK, FaunaDB, Back-end, Solution Architecture, System Architecture, API Design, LLM Integration, Back-end Development, Data, Infrastructure, Orchestration, Shopify Customizations, Payment Gateways, Billing, MVP Design, Websites, Cross-platform App Development, ElevenLabs Solutions, AI Voice Agents, Speech-to-Text (STT), Workflow Automation, Design Systems, Google Play Store, Generative Artificial Intelligence (GenAI), AI Agent Orchestration, Workflow, Multi-tenant SaaS, Identity & Access Management (IAM), Software Engineering, Cloud Infrastructure, Debugging, Communication, Vibe Coding, Agentic Coding, Web Application Design, Development, CMS, Payment Processing, Real-time Data, User Authentication, App Store Acceptance Process, Marketplaces, Affiliate Marketing, Affiliate Tracking, Trading, Financial Markets, FastAPI, Devin, In-app Purchase (IAP), Subscription Management, Push Notifications, Analytics, Conversational AI, Multi-agent Systems, LangChain, Cognigy, json-render, Generative UI (GenUI), CRM, Mobile App Development, UI Development, Text-to-Speech (TTS), Speech Recognition, Bug Fixes, Monorepos, Large-scale Projects, Azure Service Bus, OpenTelemetry, Open Source, Web Standards, Browsers, HTTP, Core Web Vitals, AI Engineering, Technical Architecture, RAG Pipelines, SEO Tools, A/B Testing, Third-party APIs, Web Applications, AI Model Integration, Workflows, Security, Privacy, Data Extraction, Reporting, Reports, Real-time Computing, Row-level Security (RLS), Banking as a Service (BaaS), Design, Pub/Sub, Mobile App Security, TradingView, Document Parsing, CSV, Data Processing, Gmail, Authentication, iOS Authentication, Email Authentication, Healthcare Software, Base44, WebSockets, OpenRouter, AI-generated Video, Cursor AI, Multi-tenant Architecture, Code Review, Code Auditing, Plugins, Performance, Inventory Management, Lightspeed, Data Security, Integrations, Chrome Extensions, Azure Blob Storage, Digital Banking, Financial Services, Finance, PDF, Support, Google Drive, Google BigQuery, Airtable, User Interface (UI), User Experience (UX), HTML5 Animations, OpenAI, Vite, Web3, Solana, Pinecone, Crypto, Chakra UI, Gatsby, Teams, Discord, Convex, Thermodynamics, Engineering
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