Sergey Kolodiy, .NET Developer in Saint Petersburg, Russia
Sergey Kolodiy

.NET Developer in Saint Petersburg, Russia

Member since September 25, 2014
Sergey is a software engineer with extensive development experience in the .NET technology stack, with strong architecture and coding skills. He loves to work on complex and business-critical tasks with full involvement, high productivity, and great enjoyment. He is a big fan of clean, testable, and maintainable code and has worked for a number of successful projects ranging from small startups to complex enterprise applications.
Sergey is now available for hire




Saint Petersburg, Russia



Preferred Environment

Git, VS Code, Visual Studio, Windows

The most amazing...

...application I've created is a tool that generates an OData REST API and a single-page web UI for any relational SQL database.


  • Senior Software Engineer

    2017 - 2018
    Shrader Group, LLC (via Toptal)
    • Designed and implemented an ETL pipeline to migrate a large amount of data from a legacy Drupal-based system to the new SQL Azure database.
    • Performed a codebase audit and fixed some serious issues related to security, database versioning, testability, and overall code quality.
    • Made a performance audit and improved the performance of critical APIs up to 10 times.
    • Implemented continuous integration pipelines in VSTS.
    Technologies: C#, .NET, Visual Studio Team Services (VSTS), Microsoft SQL Server, REST APIs, Entity Framework Core, ASP.NET Core, .NET Core, Data Integration, ETL, SQL Server Integration Services (SSIS)
  • Senior Software Engineer

    2016 - 2017
    Community Investors, Inc. (via Toptal)
    • Implemented a centralized security token service and a granular permission-based authorization system for ASP.NET Core (as opposed to coarse-grained role-based authorization).
    • Implemented an automated voicemail system with voice recognition so homeowners can register their visitors by phone and community guards will be immediately notified about new guest invitations.
    • Built a notification API for delivering various kinds of notifications to the platform users.
    • Implemented a bunch of useful ASP.NET Core extensions and middleware, such as a distributed cache with fallback logic.
    • Worked on CI-related stuff, including continuous delivery pipelines and package management.
    • Worked on payment systems integration, back-end APIs, web and desktop clients, and much more.
    Technologies: C#, .NET, Visual Studio Team Services (VSTS), Microsoft SQL Server, SendGrid, PubNub, Twilio, Identity Server, OAuth, Microservices, REST APIs, Entity Framework Core, ASP.NET Core, .NET Core
  • Senior Software Developer

    2014 - 2016
    • Implemented an administration API with AWS integration for automatic code deployment.
    • Created an administration REST service and AngularJS-powered single-page web application on top of it.
    • Worked on new features, fixed bugs, and refactored legacy code.
    Technologies: .NET, Moq, MSTest, Bootstrap, AngularJS, Windows Communication Framework (WCF), OWIN, ASP.NET Identity, ASP.NET Web API, C#
  • Software Engineer

    2014 - 2014
    • Implemented a web application for real-time server performance monitoring.
    • Created a chart control with D3.js library and helped the client avoid using commercial charting libraries.
    • Implemented a REST API for one of the projects from scratch.
    • Implemented an efficient parallel data parser for MediaWiki API.
    Technologies: C#, .NET, Moq, MSTest, Bootstrap, D3.js, jQuery, AngularJS, ASP.NET Web API, SignalR, ASP.NET, ASP.NET MVC
  • Senior Software Engineer

    2013 - 2014
    T-Systems CIS
    • Implemented new functionalities and business logic for desktop and web applications.
    • Helped integrate the software system with external services like SAP and others.
    • Provided on-site application support and helped resolve issues on the customer's site.
    • Helped to meet a bunch of important deadlines during the project lifetime.
    • Made a presentation on code review and best practices applicable to it.
    Technologies: .NET, jQuery, ASP.NET MVC, Microsoft SQL Server, Entity Framework, Windows Communication Framework (WCF), Windows Presentation Foundation (WPF), C#
  • Software Engineer

    2010 - 2013
    ETNA Software
    • Designed and developed a bunch of core system components: back-end APIs, services, and libraries for the trading platform.
    • Implemented and supported streaming and load balancing solutions for real-time market data delivery.
    • Integrated back-end components with the customer's service monitoring system.
    • Developed a market data provider with a web-based admin panel and AmiBroker integration.
    • Introduced unit testing practices to the project.
    Technologies: .NET, Moq, MSTest, NUnit, ASP.NET MVC, Microsoft SQL Server, Entity Framework, Windows Communication Framework (WCF), C#


  • Trading Platform

    A large-scale distributed platform for stock and option trading, including web and desktop client terminals.

  • ETNA Trader

    ETNA's flagship trading platform, featuring a front office, back office, and integration with third-party services and exchanges.

  • ASPro

    An enterprise software system for TÜV SÜD, a service corporation focusing on testing and certification in the industrial sector. The system consists of two major parts: a desktop workstation for the technical inspection of cars and other vehicles, and a web application for organizing drivers' license exams, surrounded by a set of back-end services and external systems.

  • Infor Learning Management System

    Infor LMS is an enterprise SaaS solution for creating, delivering, and reporting on learning throughout your internal and extended organization.

  • Real-time Server Performance Monitor

    A web application allowing administrators to remotely monitor web server performance in real time (CPU utilization, memory, disk usage, etc.), pretty much like Windows Task Manager.

  • Microsoft Certified Professional

    Microsoft Certified Professional (MCP) certification validates IT professional and developer technical expertise through rigorous, industry-proven, and industry-recognized exams. MCP exams cover a wide range of Microsoft products, technologies, and solutions.

    To validate the certification, use the following information:
    Transcript ID: 1166968
    Access Code: F4163941

  • Functional Programming Principles in Scala

    This course introduces the cornerstones of functional programming using the Scala programming language.

  • Stack Overflow

    75 answers. Active in C#, .NET, ASP.NET, ASP.NET Web API, Unit testing, and Entity­ Framework.

  • PolyGen

    PolyGen is a code generator that produces ORM layer, REST API, and a user interface for your database.

  • Unit Tests, How to Write Testable Code and Why it Matters (Publication)
    In this article, I will show that unit testing itself is quite easy; the real problems that complicate unit testing, and introduce expensive complexity, are a result of poorly-designed, untestable code. We will discuss what makes code hard to test, which anti-patterns and bad practices we should avoid to improve testability, and what other benefits we can achieve by writing testable code. We will see that writing testable code is not just about making testing less troublesome, but about making the code itself more robust, and easier to maintain.
  • Toptal Mentor
    Sergey is a mentor in the Toptal Global Mentor’s Program. This program is a partnership between Toptal and General Assembly to provide high quality mentorship for students from minority and low income backgrounds who are looking to begin their careers as professional software engineers. Sergey shows commitment to diversity in tech by mentoring a General Assembly student every week for a year, covering everything from coding tips and tricks to advice on making it in the industry.


  • Languages

    C#, T-SQL, HTML, JavaScript, Java, Markdown
  • Frameworks

    .NET Core, ASP.NET Core, .NET, ASP.NET Web API, ASP.NET MVC, Entity Framework Core, Entity, NUnit, AngularJS, ASP.NET, ASP.NET Identity, Windows Communication Framework (WCF), OAuth 2
  • Libraries/APIs

    LINQ, Moq, Entity Framework, SignalR, REST APIs, PubNub, SendGrid API, Twilio API, D3.js
  • Tools

    Microsoft Visual Studio, Azure DevOps Services, ReSharper, Git, Roslyn, Chrome Developer Tools, MSTest, Visual Studio, SendGrid, Postman, Fiddler, SoapUI, Trello, Jira
  • Paradigms

    REST, Unit Testing, Object-oriented Programming (OOP), Dependency Injection, Inversion of Control, Refactoring, Scrum, Microservices Architecture, Microservices, Object-oriented Design (OOD), Metaprogramming, Design Patterns, Azure DevOps, ETL, Test-driven Development (TDD), Agile Software Development, Functional Programming
  • Other

    SOLID Principles, Code Auditing, Single-page Applications (SPA), Identity Server, OAuth, Performance Analysis, Microsoft Data Transformation Services (now SSIS), Domain-driven Design (DDD)
  • Platforms

    Azure, Twilio, Windows, Visual Studio Code, Arduino
  • Storage

    SQL Server Management Studio, Microsoft SQL Server, Data Integration, SQL Server Integration Services (SSIS), MySQL


  • Bachelor's Degree in Information Systems and Technologies
    2005 - 2010
    Voronezh Institute of High Technologies - Voronezh, Russia


  • Microsoft Certified Professional
  • Microsoft Specialist: Programming in C#

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