Sergey Kuleshov, Developer in Limassol, Cyprus
Sergey is available for hire
Hire Sergey

Sergey Kuleshov

Verified Expert  in Engineering

MERN Stack Developer

Limassol, Cyprus
Toptal Member Since
June 8, 2016

Sergey is a full-stack and cloud web developer with a master's degree in the field of science and over 10 years of experience in the industry. With an in-depth knowledge of web technologies, he specializes in Node.js, particularly the MERN stack and DevOps, and he has extensive experience with the AWS cloud. Sergey has substantial practical experience in iOS development.


JavaScript, TypeScript, Node.js, Amazon Web Services (AWS), Web Development...
ReactiveX, React Native, GraphQL, React, Node.js, Android, iOS, Swift, Cloud...
Ember.js, Ruby on Rails (RoR), Ruby, Web Development




Preferred Environment

Git, Xcode, Visual Studio Code (VS Code), Linux, MacOS

The most amazing...

...project I've worked on was a scalable, high-load forex trading API layer based on microservice architecture.

Work Experience

Cloud Architect

2022 - PRESENT
  • Designed and implemented migration to cloud-first architecture leveraging Amazon ECS and AWS Lambda.
  • Developed a CD pipeline based on GitHub workflows with deployment to an Amazon ECS cluster.
  • Developed a NestJS module to validate Kafka messages against Glue JSON schemas.
  • Assumed an active role in migrating multiple services under an Nx-based monorepo with the common stack based on NestJS.
Technologies: JavaScript, TypeScript, Node.js, Amazon Web Services (AWS), Web Development, Docker, DevOps, GraphQL, PostgreSQL, AWS Lambda, Amazon

Team Lead and CIO

2016 - 2022
  • Designed and implemented high-performance APIs for the MetaTrader 4 (MT4) platform based on a Node.js and C++ stack with a RabbitMQ message backbone.
  • Migrated microservices to the AWS Cloud Development Kit (CDK) based on IaC best practices.
  • Led the development of a native mobile trading application for iOS and Android.
  • Developed a React and Redux back-office and client portal application.
  • Led the team implementing the company's trading application in React Native.
Technologies: ReactiveX, React Native, GraphQL, React, Node.js, Android, iOS, Swift, Cloud, UIKit, Amazon Web Services (AWS), Full-stack, CSS, Web Development, User Interface (UI), User Experience (UX), Responsive Web Design (RWD), MySQL, Docker, Project Management, DevOps, RxJS, PostgreSQL, AWS Lambda, Amazon

Senior Sofware Developer

2016 - 2016
  • Created a microservice back-end in Ruby on Rails with an EmberJS front end.
  • Worked with the project manager to define the software requirements.
  • Set up a hybrid deployment process with AWS and Digital Ocean.
Technologies: Ember.js, Ruby on Rails (RoR), Ruby, Web Development

Software Developer

2013 - 2016
  • Developed an end-to-end testing stack with Cucumber.
  • Implemented new features in a Perl-based fixed income trading back end.
  • Implemented statistics calculations and reporting for fixed income trading exchange.
  • Improved .NET and WinForms based on the client software for individual clients' needs.
Technologies: Cucumber, Ruby, .NET, C#, Perl


2012 - 2016
  • Designed and architected secure email communication solutions for iOS, Windows, and other platforms.
  • Developed a native email client for iOS supporting IMAP protocol for all popular email services.
  • Optimized Core Data for large data sets for the best user experience.
  • Implemented compatibility layer for Symantec PGP Universal Server.
Technologies: Core Data, Cocoa, Objective-C, RubyMotion, iOS, User Experience (UX)


2011 - 2013
EXA Solutions
  • Implemented an in-house data management system as a set of Rails engines backed by MongoDB.
  • Built several iOS applications with Objective-C, Core Data, and RestKit.
  • Created a multidimensional statistics system as a Ruby on Rails and a Chrome application backed by a local store.
  • Developed many eCommerce solutions integrating with PayPal and other payment gateways.
Technologies: Objective-C, MongoDB, Ruby on Rails (RoR), Ruby, PHP, Web Development, MySQL, Stripe API

Research Analyst

2008 - 2011
  • Participated in designing and executing field trials of P2P traffic optimization algorithms based on economic incentives under the EU research project SmoothIT.
  • Designed and implemented an internet protocol television (IPTV) eCommerce application.
  • Adapted and completed the quality assurance of the IPTV applications for older people under the EU research project T-Seniority.
  • Implemented video on demand (VOD) and Livestream recording for usage by clients on IPTV platforms.
  • Took part in several research projects and submitted a few proposals.
Technologies: Networking, P2P, IPTV, JavaScript, Ruby on Rails (RoR), Ruby, MySQL

Software Developer

2005 - 2007
  • Adapted SugarCRM for the needs of the business selling internet service provider (ISP) services.
  • Developed a phone number catalog for a local call center.
  • Implemented onboard registration for new customers.
Technologies: .NET, PHP

iOS Forex Trading App
As the team lead and lead iOS developer, I took the most active role in developing the trading application from the ground up, including architecture, high-load server-side APIs, and many UI/UX decisions.

Open-source CMS and e-shop based on the MERN stack. As a freelance developer, I face specific requirements to regularly develop small, low-budget sites. I needed a tool that would allow me to do it quickly and efficiently; hence, I decided to implement a custom solution and never looked back at any other commercial CMS.

Krypto Mail

Krypto Mail is a full-featured native iOS email app with integrated pretty good privacy (PGP) security, compatible with Symantec PGP, including encryption and digital signatures. Support for all IMAP/SMTP email servers. Integrated with PGP Universal Server.


One stop for all event needs—find and book locations for the event, find professionals, get quotes, and hire the best ones. Manage your budget and much more.

NDA Project

A crypto investment platform where clients can purchase ERC-20 tokens and stake them into various investment schemes. Staking and profit logic were implemented as smart contracts backed by off-chain oracles.
2007 - 2008

M.Sc. Degree in Computer Science

Royal Holloway, University of London - Surrey, UK

2002 - 2006

B.Sc. Degree in Mathematics, Computing, and Statistics

University of London - London, Distance Learning

2002 - 2005

B.Sc. Degree in Computer Science

Cyprus College - Nicosia, Cyprus


Node.js, React, RxJS, RxJava 2, RxSwift, Socket.IO, Stripe API, ReactiveX, Stripe


Git, RabbitMQ, Xcode, Cucumber


Cocoa, Rx, UIKit, React Native, Core Data, Ruby on Rails (RoR), RubyMotion, Redux, Ember.js, .NET, NestJS, Next.js, Tailwind CSS


ECMAScript (ES6), CSS, JavaScript, Swift 5, Kotlin, GraphQL, Ruby, Objective-C, SQL, TypeScript, TypeScript 2, TypeScript 3, PHP, Swift, Perl, C#, Solidity


Heroku, iOS, Linux, Android, MetaTrader 4, Amazon Web Services (AWS), Docker, AWS Lambda, Amazon, MacOS, Visual Studio Code (VS Code), Blockchain


Redis, PostgreSQL, MySQL, Amazon S3 (AWS S3), MongoDB


Test-driven Development (TDD), Responsive Web Design (RWD), DevOps

Industry Expertise

Project Management


Full-stack, Web Development, MERN Stack, User Experience (UX), IPTV, P2P, Networking, Encryption, OpenPGP, Cloud, User Interface (UI), Team Leadership, Smart Contracts

Collaboration That Works

How to Work with Toptal

Toptal matches you directly with global industry experts from our network in hours—not weeks or months.


Share your needs

Discuss your requirements and refine your scope in a call with a Toptal domain expert.

Choose your talent

Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.

Start your risk-free talent trial

Work with your chosen talent on a trial basis for up to two weeks. Pay only if you decide to hire them.

Top talent is in high demand.

Start hiring