Kostyantyn Stepanyuk
Verified Expert in Engineering
Java Developer
Lviv, Lviv Oblast, Ukraine
Toptal member since April 9, 2019
Kostyantyn is a hands-on software architect, developer, and technical lead with 25+ years of experience delivering enterprise applications, SaaS platforms, and distributed systems. His primary expertise is in TypeScript and Java, with a strong focus on cloud-native architecture on Google Cloud Platform and AWS. He has extensive experience integrating enterprise systems, including Salesforce, QuickBooks, Zoho, Stripe, and other third-party platforms.
Portfolio
Experience
- Java - 19 years
- JavaScript - 15 years
- SQL - 15 years
- Spring - 10 years
- TypeScript - 7 years
- Google Cloud - 7 years
- React - 6 years
- Amazon Web Services (AWS) - 6 years
Preferred Environment
Git, TypeScript, Cursor AI, React, Node.js, Google Cloud, AI Tools, PostgreSQL, REST
The most amazing...
...thing I've coded is a program enabling the performance analysis of thousands of servers dealing with issues that Microsoft was unable to help with.
Work Experience
Lead Software Engineer
EX AI
- Led architecture and full-stack development of a multi-tenant SaaS platform on Google Cloud Platform, owning front end, back end, cloud infrastructure, distributed workflows, and production reliability.
- Designed a modular cloud-native architecture using Node.js, TypeScript, React, Cloud Run, and asynchronous processing, focused on scalable full-stack application design.
- Built event-driven workflows for field operations, financial calculations, and integrations with Salesforce, Stripe, QuickBooks, Amazon SP-API, Zoho CRM, DocuSign, and Google Workspace APIs.
- Developed distributed data systems using PostgreSQL (Cloud SQL) and Google Cloud Firestore for transactional workloads, real-time data, and scalable cloud-native persistence.
- Designed web scraping and browser automation solutions for data extraction, workflow automation, and integrations where third-party APIs were unavailable or limited.
- Led hands-on technical delivery across front-end and back-end systems, including implementation, production debugging, and reliability and performance improvements.
Delivery Manager
Edvantis
- Created project proposals, including budgets and schedules.
- Spearheaded work with new accounts, establishing project processes.
- Contributed to the creation of project technical solutions (typically cloud-based web applications).
- Facilitated growth in terms of team size and profitability.
- Ensured customer satisfaction by resolving complaints and conflicts.
Project Lead
Edvantis
- Oversaw projects with a total staff of up to 15 engineers.
- Spearheaded and successfully developed a large infrastructure management software solution based on C#/.NET and various Windows APIs.
- Designed and implemented Realty Leads, a cloud-based Java solution that provides potential realty buyers and agents with the best matches among many thousands of properties available in the US market.
- Led the development of Festival Genius, a Java web application hosting films and schedules information for the US, Canadian, and European film festivals.
- Developed a web-based management solution for leads, contacts, and sales on behalf of a clear span protective structure provider.
- Managed the workflow of thousands of leads, supporting local and cloud deployments.
Lead Software Engineer
SoftServe
- Led the development of lean operations management system modules for a large ERP solution for a lean manufacturer (J2EE/Struts stack).
- Implemented a number of memory and performance optimization projects (primarily a Java/web stack).
- Developed a Java ME mobile application for photo image enhancements.
- Constructed an insurance carrier and agency workflow management system (Java/Hibernate stack).
- Participated in the creation of technical proposals for potential customers.
Senior/Lead Software Engineer
ISD
- Started as a senior Java engineer eventually leading a group of engineers.
- Designed and developed a project-and-resource management solution based on a Workflow framework.
- Developed a Microsoft project interface for a task management solution.
- Gained Java expertise from working within the company.
- Created a contract management solution (porting from Microsoft Access to Java/web).
Software Engineer
Ulybin GmbH
- Developed a small-but-complex routine that calculates the results of an intersection of 3D objects and returns the remaining parts as a single object (C++).
- Developed an RTF-to-HTML-to-RTF converter (C++).
- Implemented a set of Java classes to be used in ASP pages as COM objects that provide content management functionality, automatic rendering and processing of HTML documents, and logging information.
- Created a set of EJBs for managing various business objects like financial contracts, vehicles, applications, and so on.
- Built administrative UIs for a financial application (JSP).
Experience
EE and Audit SaaS platform
• Audit Logic and Field Data Acquisition: Standardized mobile framework for structured field data collection with comprehensive offline synchronization.
• Financial and ROI Modeling: Automated engine for calculating energy-savings proposals, ROI reports, and utility rebate exports with dynamic margin control.
• Inventory Database: Tenant-specific system for managing components along with their pricing, enabling scalable solution design and consistency across projects.
• Production Data Pipeline: Automated generation of technical bill-of-materials (BOM) and installation documentation to synchronize sales and field operations.
• Core Development: Full-stack TypeScript (Node.js and React).
• Cloud and Collaboration: Google Cloud, Google Workspace.
• Project Management and CRM: ClickUp, Salesforce, Zoho CRM.
• Financials and Payments: QuickBooks, Stripe.
• Logistics and Compliance: Amazon SP (Selling Partner) API, DocuSign.
Realty Leads
Hybrid architecture combining a core monolithic back end with independently deployed modular scraping services responsible for extracting, normalizing, and synchronizing data from hundreds of real estate websites.
Distributed scraping infrastructure designed for resilient large-scale data collection with rate-limit handling, fault tolerance, and normalization across heterogeneous external sources.
Data processing workflows for property listing deduplication, enrichment, and rule-based matching to buyers and agents.
AWS-based deployment architecture with core back end hosted on Elastic Beanstalk and scraper services implemented as independent Lambda-driven components.
Physical Therapy Portal
It consists of two major components:
• Support Chat—an embeddable chat widget that clinics will host on their websites. In addition to traditional SaaS support chat features, it allows the scheduling of patient visits and money deposits for reservation. The chat also features advertisements for physical therapy products directly related to the patient’s specific injury.
• Portal—a web application for physical therapists handling chats and for clinics, setting up patient schedules. The portal is responsible for selecting the type of physical therapy based on the patient's injury; it also facilitates payment workflows.
Video Presentation Ecosystem
Performance Monitor
Education
Master's Degree in Applied Mathematics
Ivan Franko National University of Lviv - Lviv, Ukraine
Skills
Libraries/APIs
React, Google Workspace APIs, Node.js, REST APIs, Stripe, Stripe API, Spring REST, Google APIs, jQuery, jQuery UI, Java Message Service (JMS), Zoho API, QuickBooks API, Google Maps API, Playwright, JDBI, Stripe Connect, LinkedIn API, Puppeteer, Google Calendar API, Facebook API, Windows API, Beautiful Soup
Tools
Git, Apache Tomcat, Apache, Amazon Simple Email Service (SES), Amazon Simple Queue Service (SQS), Claude, Terraform, Zoho Inventory, Claude Code, ChatGPT, Expo, GIS, Gradle, NPM, Amazon Elastic Container Service (ECS), RabbitMQ, Firebase Cloud Messaging (FCM)
Languages
Java, JavaScript, TypeScript, SQL, HTML, HTML5, Python, GraphQL, Zoho Deluge, CSS, C, PHP, C#, C++, C#.NET
Frameworks
Spring, Apache Struts, Hibernate, Jakarta Server Pages (JSP), Spring Boot, Spring Security, .NET, OAuth 2, Angular, AngularJS, NestJS, Next.js, Tailwind CSS, Selenium, Express.js, ZK, Spark, React Native
Paradigms
REST, Agile, Object-oriented Programming (OOP), Functional Programming, Extreme Programming, Scrum, Microservices, Service-oriented Architecture (SOA), Automation, Role-based Access Control (RBAC), App Development, UI Design
Platforms
Amazon Web Services (AWS), Google Cloud Platform (GCP), Firebase, Google AppSheet, Google App Engine, JBoss, WebSphere, Docker, Salesforce, AWS Lambda, Zoho CRM, Calendly, Vercel, Windows, MacOS, Eclipse, Jakarta EE (Java EE or J2EE), Linux, Oracle, Heroku, Kubernetes, Visual Studio Code (VS Code)
Storage
PostgreSQL, Google Cloud, Relational Databases, Spring Data, Amazon S3 (AWS S3), Microsoft SQL Server, MySQL, NoSQL, Amazon DynamoDB, Data Pipelines, MongoDB, Redis
Industry Expertise
Project Management
Other
Ajax, TypeORM, Full-stack, Full-stack Development, API Integration, Web Development, APIs, Artificial Intelligence (AI), Software Development, Minimum Viable Product (MVP), RESTFul APIs, Browser Automation, Web Scraping, SaaS, Software as a Service (SaaS), Security, Technical Leadership, Back-end, Software Architecture, Software Design, Third-party APIs, Leadership, Back-end Development, Front-end Development, Authorization, Database Schema Design, Webhooks, Cloud Infrastructure, Code Auditing, Payment APIs, OAuth, Front-end, Solution Architecture, System Architecture, Billing, MVP Design, Multi-tenant SaaS, Web Applications, Architecture, Amazon Route 53, Enterprise Java Beans (EJB), Cursor AI, GoHighLevel API, Hibernate 3, AI Tools, Modular, Integration, Zoho, User Experience (UX), User Interface (UI), Agentic Coding, Offline Data Synchronization, Data Scraping, Scraping, Deluge, Order Management, Fulfillment, Stripe Subscriptions, DocuSign, Finance, AI Integration, AI-assisted Development, Data Engineering, CRM, OpenAI, Web Crawlers, LinkedIn, Startups, Base44, Cloud, Serverless, Payments, CI/CD Pipelines, Booking Systems, WebSockets, Identity & Access Management (IAM), Data Modeling, Workflow Automation & System Integration, Progressive Web Applications (PWAs), Data Privacy, Pipelines, Reporting, Reports, User Roles, Workflows, Geolocation, Maps, Algorithms, Document Parsing, AI Automation, Data Processing, CSV, Gmail, Workflow Automation, Cost Analysis, Service Delivery Management (SDM), Applied Mathematics, Supabase, Gemini API, Deepgram, Fintech, Supabase Auth, Vite, General Data Protection Regulation (GDPR), Quarkus
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