Sergey Okhotnikov, Developer in L'Eliana, Spain
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Sergey Okhotnikov

Verified Expert  in Engineering

Software Developer

L'Eliana, Spain
Toptal Member Since
July 15, 2021

Sergey has been working remotely for more than ten years. He succeeded in completing remote projects and building remote teams long before it became the main development trend. He acted as a developer and was a part of the QA team in his last working place, where he designed and built the back end and administrative front end from scratch. Sergey is a professional who looks forward to working on high-quality projects—especially in the educational, healthcare, gaming, and IoT industries.


TypeScript, JavaScript, Java, Python, PostgreSQL, PostGIS, Mapbox, Stripe...
Toptal Clients
Java, JavaScript, SQL, Amazon Web Services (AWS), REST...
ANAV/Scientific Entertainment
Java, Spring, PostgreSQL, JavaScript, TypeScript, React, Unity, C#, Spring Boot...




Preferred Environment

MacOS, Linux, IntelliJ IDEA

The most amazing...

...thing that I've designed and implemented is the education robot platform with Arduino controller, Unity game, and Java server.

Work Experience

CTO | Full-stack Developer

2022 - PRESENT
  • Created the project's architecture and infrastructure from scratch.
  • Built back-end services with Python, Node.js, and Java and deployed them to AWS.
  • Developed a web application with React, TypeScript, and Next.js.
  • Integrated Stripe and MapBox libraries to the project.
Technologies: TypeScript, JavaScript, Java, Python, PostgreSQL, PostGIS, Mapbox, Stripe, AWS Lambda, Serverless, Spring, Next.js, GitHub, Docker, React, Microservices, Responsive UI, User Experience (UX), Technical Leadership, Leadership, QR Codes, Material UI, Java 11, JavaScript MVC, Technical Architecture, Cloud Infrastructure, Web Development, Mapbox GL, JSON, API Integration, Webhooks, Web Mapping, UI Design, Databases, Responsive Layout, Vercel, Serverless Architecture, DOM, Jest, DevOps, UX Design, Amazon CloudFront CDN, CTO, Startups, Airtable, Product Development, Payment Gateways, Lambda Architecture, CSS3, JavaScript Libraries, Web App Development, NPM, Unit Testing, Amazon Simple Queue Service (SQS), Cypress, Axios, Technical Consulting

Back-end and Full-stack Developer

2021 - PRESENT
Toptal Clients
  • Developed Auth0 integration for the back end using Java Spring and Rest client.
  • Set up and developed performance tests using REST API, API Gateway, AWS Lambda, and CloudWatch.
  • Developed the email parsing flow using AWS Route 53, SES, S3, and Lambda.
  • Fixed performance issues of AWS Lambda and API Gateway.
Technologies: Java, JavaScript, SQL, Amazon Web Services (AWS), REST, Amazon Simple Email Service (SES), AWS Lambda, Amazon S3 (AWS S3), Amazon Route 53, Amazon API Gateway, Spring, Hibernate, Auth0, MySQL, API Architecture, Swagger, REST APIs, Git, Node.js, APIs, Back-end, JSON Web Tokens (JWT), Back-end Development, OAuth, Microservices Architecture, Serverless, Lambda Functions, CI/CD Pipelines, Integration, DocumentDB, AWS Cloud Architecture, TypeScript, Java 8, NoSQL, Cloud Infrastructure, Web Development, JSON, API Integration, Webhooks, Databases, Serverless Architecture, DevOps, Code Review, Lambda Architecture, JavaScript Libraries, Web App Development, NPM, Unit Testing, Amazon Simple Queue Service (SQS)

Senior Software Developer

2016 - PRESENT
ANAV/Scientific Entertainment
  • Created and developed the back end and admin front end from scratch using Java, PostgreSQL, Redis, AWS, React, and Angular. The service covers all needs concerning the client, license, and purchase management for the educational software.
  • Implemented developer tools for the team, such as an online dictionary, quest, content, and level editors. AngularJS editors were developed with MongoDB data storage and a REST API service for multimedia client access.
  • Designed and built a user behavior analytics system based on AWS S3 and Apache Spark.
  • Built a teacher-student communication and file-sharing system using a WebSocket server for chat and S3 with CloudFront and a link signing service for file sharing.
  • Managed the teamwork and set up tools including Git, task trackers, and Slack. Planned milestones and wrote tasks for sprints, trained team members, and planned and conducted team meetings and information-sharing sessions.
Technologies: Java, Spring, PostgreSQL, JavaScript, TypeScript, React, Unity, C#, Spring Boot, Docker, Docker Compose, Docker Hub, Architecture, Web Architecture, Full-stack, WebSockets, Redis, Apache Spark, Amazon Web Services (AWS), Amazon API Gateway, Amazon Cognito, TypeScript 3, JavaScript 6, MongoDB, Azure, GitHub API, Redux, React Router, Front-end, API Architecture, REST APIs, Firebase, Firebase Cloud Functions, Git, Figma, Front-end Development, Node.js, APIs, Back-end, JSON Web Tokens (JWT), Back-end Development, OAuth, Software Architecture, Microservices Architecture, Lambda Functions, CI/CD Pipelines, Integration, HTML, CSS, HTML5, Angular, Unity3D, Remote Team Leadership, Spark, GitLab, Technical Leadership, Requirements Analysis, Leadership, Java 8, JavaScript MVC, NoSQL, Machine Learning, Cloud Firestore, Technical Architecture, Cloud Infrastructure, Web Development, JSON, API Integration, Webhooks, UI Design, Team Leadership, Databases, DOM, DevOps, UX Design, Amazon CloudFront CDN, Code Review, Amazon DynamoDB, Product Development, Project Management, Mobile, Kubernetes, Batch File Processing, Google Cloud Platform (GCP), CSS3, JavaScript Libraries, Sass, Web App Development, NPM, Unit Testing

Software Developer

2013 - 2016
  • Developed pipeline for document transformation from word and text files to database records.
  • Implemented tests and validation algorithm for incoming documents.
  • Wrote guides and requirements for documentation providers.
Technologies: Java, MySQL, Delphi, XML, Linux, Apache Kafka, Multithreading, Spring, Google Cloud, REST APIs, Git, APIs, Back-end, JSON Web Tokens (JWT), Back-end Development, Elasticsearch, Databases, Unit Testing

Lead Product Manager

2004 - 2013
PIPE Studio
  • Created product design for major game series of the studio.
  • Trained, evaluated, and managed junior product managers.
  • Conducted negotiations about product design with partners and customers.
  • Designed, developed, and tested product prototypes.
Technologies: Product Design, Unity, C#, Game Design, Game Development, Architecture, User Interface (UI), User Experience (UX), Games, Gaming, 2D Games, 3D Games, Requirements Analysis, Leadership, UI Design, Team Leadership, UX Design, Product Development, Technical Consulting

Pascal Developer and Technical Writer

2001 - 2004
  • Wrote instructions and user guides for new company software products.
  • Developed a user guide library program for indexing and searching documentation.
  • Conducted software testing for special use case description purposes.
Technologies: Delphi, Pascal, SQL

Software Developer

1998 - 2001
Sikkens Ukraine
  • Developed warehouse management system for wholesales company.
  • Maintained warehouse management system for wholesales company.
  • Implemented product sales report and prediction system.
Technologies: Delphi, SQL, User Interface (UI), Windows

B2C and P2P rental platform with Next.js front- and back-end services in Java, Node.js, and Python. The service works with geolocation and geospatial queries, so most items are probably invisible outside Spain.

Toptal React Accelerator Graduate

The Toptal React Accelerator is an exclusive learning program that educates JavaScript developers in React, NextJS, Redux, and GraphQL. This is a 2-month program that consists of rigorous learning exercises and hands-on activities along with a stringent evaluation process, comprehensive learning assessments, and an Invoice Management System. Within this invoicing application, users are able to track invoices, clients, and company information.
Personal website with an old-style text dialog system. A user could access all functions without a mouse with numeric keys, Esc, and Enter. Also, text animation was implemented for old-style text typing effects and text progress bars.

I was working on a project called “Multimedia physics lab for elementary schools”. I've built back end and admin tools from scratch, including authorization, customer management, developer tools, and user behavior analytics. Also, I hired and trained other developers.

Native Speech Recognition plugin

Paid Unity plugin for speech recognition. This project includes iOS and Android libraries, Unity integration code, and a test scene. With this plugin, Unity developers can easily integrate speech recognition into their game,

Professor Drozdov School
Online educational platform for elementary schools. I built a back end and admin tools, including content management and delivery system, class management, lesson scheduling, client notifications, chatrooms for students and teachers.
1993 - 1999

Bachelor's Degree in Computer Science

National Technical University of Ukraine - Kiev, Ukraine

MARCH 2023 - MARCH 2026

AWS Certified Developer – Associate

Amazon Web Services Training and Certification


Toptal React Accelerator Graduate

Toptal, LLC


React, REST APIs, Node.js, React Router, Stripe, Mapbox GL, GitHub API


Amazon CloudFront CDN, GitHub, WebStorm, Apache Maven, GitLab, Git, NPM, Amazon Simple Queue Service (SQS), IntelliJ IDEA, Mathematica, Figma, Amazon Simple Email Service (SES), Amazon CloudWatch, Amazon Elastic Container Service (Amazon ECS), Amazon Elastic Container Registry (ECR), Docker Compose, Docker Hub, Amazon Cognito, Auth0


Spring, Spring Boot, JSON Web Tokens (JWT), Next.js, AngularJS, Redux, Unity3D, Material UI, JavaScript MVC, Jest, Cypress, Spark, Unity, Angular, Apache Spark, Hibernate, Swagger


Java, SQL, JavaScript, HTML, CSS, Java 8, Java 11, TypeScript, C#, HTML5, CSS3, Sass, Swift, Python, Pascal, C++, Delphi, XML, GraphQL, TypeScript 3, JavaScript 6


UX Design, Microservices, REST, API Architecture, Microservices Architecture, Requirements Analysis, Mobile Development, UI Design, Responsive Layout, Serverless Architecture, DevOps, Unit Testing, Management, Web Architecture, Lambda Architecture


Amazon Web Services (AWS), Android, Docker, AWS Lambda, Firebase, Mapbox, Vercel, Azure, Linux, Apache Kafka, MacOS, Kubernetes, Visual Studio Code (VS Code), Amazon EC2, Windows, iOS, Mobile, Google Cloud Platform (GCP)


Databases, Amazon S3 (AWS S3), NoSQL, JSON, PostgreSQL, Redis, MongoDB, MySQL, SQL Stored Procedures, Cloud Firestore, Elasticsearch, Google Cloud, Amazon DynamoDB, PostGIS

Industry Expertise

Project Management


Product Design, Back-end, Full-stack, Front-end, Front-end Development, APIs, Back-end Development, Lambda Functions, User Experience (UX), Gaming, 2D Games, Web Development, API Integration, Webhooks, Web App Development, Remote Team Leadership, Game Development, User Interface (UI), Technical Leadership, Architecture, Chakra UI, OAuth, Software Architecture, Serverless, Integration, Games, 3D Games, DocumentDB, QR Codes, Technical Architecture, Cloud Infrastructure, Team Leadership, DOM, CTO, Startups, Code Review, Product Development, Payment Gateways, Batch File Processing, JavaScript Libraries, Axios, Technical Consulting, Marketing Mix, Electronics, Physics, Game Design, Machine Learning, Responsive UI, RESTful Microservices, WebSockets, Multithreading, Amazon API Gateway, Amazon Route 53, Firebase Cloud Functions, CI/CD Pipelines, AWS Cloud Architecture, Leadership, Web Mapping, Airtable

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