Sebastian is available for hire

Sebastian Kalinowski

Verified Expert in Engineering

Full-stack Developer

Location

Warsaw, Poland

Toptal Member Since

October 11, 2019

Sebastian is a .NET developer specializing in back-end layer development. He has over a decade of professional experience within banking, financial, and recruitment industries. He’s also comfortable in front-end development (React), system design, and architecture. Sebastian has successfully worked with numerous clients to define requirements, design new system elements, implement new functionalities, and optimize existing systems.

Full-stack C#C#.NET React .NET Core T-SQL (Transact-SQL).NET Visual Studio Windows CSS HTML5 SQL Scrum TypeScript Agile

Portfolio

Santander Consumer Bank — Nordics

Azure, REST, TypeScript, React, .NET Core, JavaScript, C#

Citi

Microsoft SQL Server, Couchbase, Apache Kafka, RabbitMQ, .NET, C#

KMD Poland

Angular, Azure, AngularJS, SQL, IBM Db2, Web API, JavaScript, C#

Experience

Full-stack - 10 years .NET - 10 years T-SQL (Transact-SQL) - 10 years C# - 10 years JavaScript - 8 years TypeScript - 3 years React - 3 years .NET Core - 2 years

Availability

Part-time

Preferred Environment

JetBrains Rider, Visual Studio Code (VS Code), Visual Studio, Windows

The most amazing...

...project I've worked on was a highly available risk calculation system processing transactions worth billions of dollars.

Work Experience

Senior .NET Developer

2018 - PRESENT

Santander Consumer Bank — Nordics

Designed and implemented an internal recurring task scheduler and tracker (front end and back end).
Designed and implemented a tax statement's administrative app using React (front end and back end).
Implemented back-end parts of the PSD2 directive (Consent, Cards).
Configured CI/CD pipelines in Azure DevOps and Octopus Deployment.
Ensured high quality of the project by proposing and implementing enhancements.
Maintained some internal projects.
Completed OAuth2 and OIDC configurational tasks.
Worked in scrum and scrum with kanban environments.
Served as an API Foundation team member—providing guidelines for organizing about API interfaces.

Technologies: Azure, REST, TypeScript, React, .NET Core, JavaScript, C#

Senior .NET Developer

2017 - 2018

Citi

Redesigned components of the distributed batch system calculating the risk of G10 Rates trades.
Rearchitected and reimplemented critical component of an existing system which allowed slicing it and reducing its complexity.
Improved the existing codebase and paying off technical debt.
Investigated and solved non-trivial issues on daily basis.
Ensured high quality of the project by proposing and implementing enhancements.
Gave technical presentations for team members.

Technologies: Microsoft SQL Server, Couchbase, Apache Kafka, RabbitMQ, .NET, C#

Senior Full-stack .NET Developer

2016 - 2017

KMD Poland

Developed new modules for the application for Danish utility companies supporting administration, billing, metering, task management (frontend and backend).
Implemented new features for the application supporting job center employees in Denmark (frontend and backend).
Ensured high quality of the project by proposing and implementing enhancements.
Worked in scrum.

Technologies: Angular, Azure, AngularJS, SQL, IBM Db2, Web API, JavaScript, C#

Senior .NET Developer

2015 - 2016

Grupa Pracuj

Implemented internal application supporting management of job offers for the largest recruitment platform in Poland.
Refactored flaws of current architecture.
Optimized performance of existing systems.
Ensured high quality of projects by proposing coding conventions, service contracts, code reviews and GitHub workflow in the team.
Mentored junior team members.
Worked in a scrum environment.

Technologies: CQRS, NancyFx, AngularJS, Akka.NET, RabbitMQ, Microsoft SQL Server, Entity Framework, Web API, JavaScript, C#

.NET Developer

2014 - 2015

mBank

Implemented currency exchange (FX) and payment basket modules for the mBank main website.
Built new modules for an existing corporate CRM, optimized existing code.

Technologies: jQuery, ASP.NET MVC, Microsoft SQL Server, LINQ to SQL, Windows Forms (WinForms), JavaScript, C#

.NET Developer

2011 - 2014

EBR-IT

Implemented Idea4Work: an application that simplifies the management of programmatic projects.
Added new features to Deal Manager: a system that helps to manage a real estate agency in Australia.
Implemented projects like PalletPlus (asset management and tracking) and Document Control (versioning documents) for a customer from Australia.
Designed parts of the system (including architecture), creating reports and unit and integrated tests.
Applied domain-driven design (DDD), CQRS, and event sourcing patterns.
Coordinated a small team of three junior programmers.

Technologies: Entity Framework, Kendo UI, Telerik Reports, Controls, Telerik, jQuery, Bootstrap, NServiceBus, SQL, RavenDB, ASP.NET MVC, Windows Presentation Foundation (WPF), JavaScript, C#

Junior .NET Developer

2010 - 2011

Pentegy

Implemented a certificate application for the Polish Office of Electronic Communications (e-learning, examination, and issuing certificates).
Adjusted and integrated existing open-source OCR/OMR software with the certificates app project.
Implemented the back end of mobile app for one of Ukrainian's banks.
Composed technical documentation.

Technologies: PHP, Microsoft SQL Server, Windows Communication Framework (WCF), Web Services, MySQL, C#

Experience

Scheduler and Workflow Service

An internal project used by other developer teams for scheduling and execution tracking of recurring tasks. The project was built on top of one of the open-source schedulers and .NET Core in RESTful microservices architecture with a front end built with React and TypeScript.

Simpliciti

This was an internal project that involved a complex batch system calculating the risk of G10 Rates trades. The system had to be highly available and work 24/7. The project was built using .NET, RabbitMQ, SQL Server, and Couchbase. Since the build of the project, I've added new features and refactored one of the critical components.

EasyEnergy

This is an application for utility companies that supports administration, billing, metering, and task management. The project was supposed to replace some small legacy WinForms applications with one, coherent application built with AngularJS. The back end was built with the .NET framework and DB2 as a persistence layer.

Skills

Languages

C#, C#.NET, TypeScript, JavaScript, T-SQL (Transact-SQL), XAML, ECMAScript (ES6), CSS, HTML5, SQL, HTML, PHP

Frameworks

.NET Core, .NET, Entity Framework Core, Windows Presentation Foundation (WPF), ASP.NET Core, OAuth 2, Angular, NancyFx, ASP.NET MVC, Bootstrap, Windows Communication Framework (WCF), AngularJS, Kendo UI, ASP.NET

Libraries/APIs

React, Entity Framework, Windows Forms (WinForms), Web API, jQuery, NServiceBus

Other

Full-stack, APIs, RESTful Microservices, Front-end Development, Akka.NET, Controls, Web Services, Cloud, OpenID Connect (OIDC)

Tools

Visual Studio, ReSharper, C#.NET WinForms, JetBrains Rider, Telerik Reports, RabbitMQ, LINQ to SQL

Paradigms

Agile, Scrum, Pair Programming, CQRS, Object-oriented Programming (OOP), REST

Platforms

Windows, Azure, Visual Studio Code (VS Code), Apache Kafka, Telerik

Storage

SQL Server 2016, Couchbase, Microsoft SQL Server, IBM Db2, RavenDB, MySQL

Education

2013 - 2014

Postgraduate Coursework in Project Management

Warsaw University of Technology - Warsaw, Poland

2011 - 2012

Master's Degree in Computer Science

Warsaw University of Technology - Warsaw, Poland

2007 - 2011

Bachelor's Degree in Computer Science

Warsaw University of Technology - Warsaw, Poland

Certifications

MAY 2020 - PRESENT

Azure Fundamentals

Microsoft

MAY 2014 - PRESENT

PRINCE2 Foundation

PRINCE2®