Sergey Smyshlyaev, Developer in Belgrade, Serbia
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Sergey Smyshlyaev

Verified Expert  in Engineering

Software Developer

Belgrade, Serbia
Toptal Member Since
July 29, 2021

Sergey is a senior software developer with 12+ years of experience. For the past six years, he has focused on web applications with React and mobile applications with React Native. He has worked on projects that now serve millions of customers and is passionate about finding solutions to complex problems. Sergey is always looking for challenging projects where his technical skills can have an impact.


WeMoney Pty Ltd
React Native, React, Redux, TypeScript, JavaScript
Droplet Tech Ltd.
React Native, Redux, TypeScript, Redux Toolkit, Unit Testing, Jest, Firebase...
Elemy - Main
React, TypeScript, Storybook, GraphQL, Hasura, Jest




Preferred Environment

MacOS, WebStorm

The most amazing...

...thing I've done was launching the Hippo drug discount application as a part of the founding team.

Work Experience

Senior React Native Developer

2023 - 2023
WeMoney Pty Ltd
  • Improved startup time and performance of the application.
  • Upgraded React Native and related libraries to up-to-date versions.
  • Fixed multiple bugs related to React Native and library upgrades.
Technologies: React Native, React, Redux, TypeScript, JavaScript

React Native Developer

2022 - 2023
Droplet Tech Ltd.
  • Participated in the development of a React mobile application from scratch.
  • Built the component library and storybook for the project.
  • Implemented the business logic in a reusable manner within a package re-used in a web app.
Technologies: React Native, Redux, TypeScript, Redux Toolkit, Unit Testing, Jest, Firebase, Minimum Viable Product (MVP)

Front-end React Developer

2022 - 2022
Elemy - Main
  • Developed, as part of the team, a new iteration of an internal tool aimed at reducing operational costs.
  • Took part in developing React component library used by multiple projects in the company.
  • Participated in engineers' on-call rotation and fixed various bugs in the company's web projects.
Technologies: React, TypeScript, Storybook, GraphQL, Hasura, Jest

Senior Full-stack Developer

2021 - 2022
Toptal Client
  • Built a logistics and operations management dashboard for a large US medical corporation from scratch as a part of a small team.
  • Worked on an ETL pipeline between a data warehouse in the cloud and a database powering the dashboard.
  • Helped shape the technical coordination and development process as the team grew.
Technologies: JavaScript, React, Next.js, GraphQL, Hasura, PostgreSQL, Full-stack, Full-stack Development, Material UI

Senior Software Engineer

2018 - 2021
Centrica Connected Homes
  • Participated in the complete rewrite of the app from native code to React with Redux and Redux-saga. Participated in the launch of the rewritten version, resulting in an increase in the app rating from 3.0 to 4.5 stars.
  • Played a key role in launching multiple devices and services, including the Hive outdoor camera, HomeShield security system, and Hive Heating Plus subscription.
  • Fixed complex WebRTC bugs by introducing extensive debugging tools and patching the React Native WebRTC library, including native code.
Technologies: React Native, WebRTC, JavaScript, Flow, Redux, Redux-Saga, Jest, Serverless Framework, AWS Lambda

Senior Software Engineer

2017 - 2018
Hippo Technologies LLC
  • Participated in the development and launch of the Hippo mobile app with React Native, MobX, and TypeScript.
  • Implemented and launched the internal customer service dashboard web application with React, Redux, and TypeScript.
  • Participated in the development and launch of the Hippo web app with React, MobX, and TypeScript.
Technologies: JavaScript, React, React Native, Node.js, TypeScript

Senior Software Engineer

2016 - 2017
Epic Software Development
  • Participated in developing a new version of a B2B web app in the area of risk management, assessment, and audit with React and Redux.
  • Implemented an SSO solution based on SAML 2.0 and Shibboleth and automated the solution deployment via Docker and Docker Compose.
  • Worked on a B2B web app back end using Node.js and PostgreSQL.
Technologies: JavaScript, Node.js, SAML-auth, Docker, Shibboleth, React, Express.js, Full-stack, Full-stack Development, Material UI

Senior Software Engineer

2016 - 2016
Mera Networks
  • Co-developed a WebRTC-based SDK for a contact center solution from one of the largest business communication providers in the United States.
  • Architected a solution for real-time communication between smart devices and websites.
  • Co-developed a white label social app aimed at image analysis (resel) and a health-oriented enterprise social network.
Technologies: JavaScript, React, React Native, Sails.js, PHP, Angular, Java, WebRTC

Senior Software Engineer

2014 - 2015
  • Implemented a new UI for the broadcast monitoring system using React.
  • Migrated the old broadcast monitoring system UI from Google Web Toolkit (GWT) to React.
  • Worked on back end of the broadcast monitoring system written in Java with Spring and Hibernate.
Technologies: React, JavaScript, Java, Spring, GWT

Senior Software Engineer

2013 - 2014
  • Played a key role in implementing a new generation of the contact center back end in Erlang.
  • Fixed bugs in the contact center front-end integration with Salesforce.
  • Fixed bugs in the contact center call routing and matching back end.
Technologies: Java, Erlang, JavaScript

Software Engineer

2008 - 2013
Mera Networks
  • Developed real-time software for GSM and UMTS core network nodes while working in an outsourcing team for a leading vendor of mobile network equipment.
  • Built an SIP-based VoIP solution while working in an outsourcing team for a leading VoIP solution vendor.
  • Developed the front end and back end for a network monitoring tool used by mobile phone and internet providers while working in an outsourcing team for a measurement and monitoring solution vendor.
Technologies: C, SS7, Java, Java EE, Groovy, Grails, JavaScript, Ext JS

Hippo Drug Discount Application

A web and mobile app that allows consumers to find prescription drugs at discounted prices. As a member of the founding team and senior software engineer, I played a pivotal role in developing and launching the web and mobile apps. One of my focus areas was the internal customer service dashboard web application.
2003 - 2009

Master's Degree in Physics

Lobachevsky University of Nizhny Novgorod - Nizhny Novgorod, Oblast, Russia


React, WebRTC, Node.js, Redux-Saga


Flow, MATLAB, LabVIEW, Shibboleth, WebStorm, Redux Toolkit


React Native, Redux, Sails.js, Angular, Spring, GWT, Grails, Ext JS, Next.js, Express.js, Material UI, Jest, Serverless Framework


JavaScript, TypeScript, Java, PHP, Erlang, C, Groovy, GraphQL


Unit Testing


Docker, Java EE, MacOS, Firebase, AWS Lambda


Hasura, PostgreSQL


SAML-auth, SS7, Mobile Apps, Web App Development, Dashboards, Full-stack, Full-stack Development, Storybook, Minimum Viable Product (MVP)

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