Csaba Keri, Developer in Zürich, Switzerland
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Csaba Keri

Verified Expert  in Engineering

Full-stack Developer

Zürich, Switzerland
Toptal Member Since
October 9, 2020

Csaba is a full-stack developer who's been working with C# and SQL since 2001 and as an architect since 2015. Csaba is comfortable working with companies of all sizes using both the Waterfall and Agile methodologies and has experience in banking & finance (ten years), aviation (six years), and TV/radio stations (four years). Csaba also excels at database & application architecture planning, implementation, quality assurance, data transformation (ETL), and performance optimization.


DXC Technology
ASP.NET Core, .NET 6, C#, Splunk, OpenShift, Argo CD, Amazon S3 (AWS S3)...
Exemplar Human Services, LLC
C#.NET, .NET Core, .NET, Entity Framework Core, .NET 4, .NET 5, C#...
Mortgage300 Corporation
C#.NET, C#, Azure, Microsoft SQL Server, Xamarin, Twilio API, Telerik...




Preferred Environment

Kanban, Scrum, Web MVC, C#.NET, SQL, Slack, Visual Studio, Windows

The most amazing...

...thing I've developed is the entire application for a real shop, which covered all possible activities: billing, storage maintenance, and a lots of reports.

Work Experience

Senior Consultant

2022 - PRESENT
DXC Technology
  • Developed a package tracking app for package deliveries. All package status changes generated one or more events sent to our (several) microservices through Kafka messaging. The whole app was containerized into Red Hat pods.
  • Created a demo application for a containerized environment with a basic application. As a demo, I created automatic BDD test cases with Cucumber, called Selenium test steps, and made a Jenkins pipeline that calls the tests after every push.
  • Recreated a Google Analytics report in Looker Studio (previously Google Data Studio) based on BigQuery data sources, using the standard and custom GA4 metrics and dimensions.
  • Containerized a few C# Angular applications to run in Red Hat Openshift 4 pods.
Technologies: ASP.NET Core, .NET 6, C#, Splunk, OpenShift, Argo CD, Amazon S3 (AWS S3), Apache Kafka, Elastic, Google BigQuery, Google Data Studio, Microservices Architecture, Angular, Cucumber, Selenium, Amazon DynamoDB

.NET Expert

2022 - PRESENT
Exemplar Human Services, LLC
  • Reviewed the entire code of a human performance management and analytics tool for a human services company.
  • Upgraded from .NET 5 to .NET 6 and optimized performance.
  • Integrated Windows Defender into the application: Windows Defender is called for every uploaded file.
  • Added a feature to create Microsoft Teams meeting under multiple users.
  • Integrated a JQuery-based calendar to make the meetings more visible.
  • Added BDD and Nunit test cases which covered all the testable methods.
  • Optimized the ASP.NET Core 6 Web UI—removed redundant code and enhanced partial view usage.
  • Refactored the e-signing (signing a document online with previously registered signatures) process so that a new document gets automatically parsed instead of creating the code for all the new document types one by one.
Technologies: C#.NET, .NET Core, .NET, Entity Framework Core, .NET 4, .NET 5, C#, Entity Framework, .NET 6, Behavior-driven Development (BDD), NUnit, NSubstitute, SQL, ASP.NET Razor, Databases, Agile, Test-driven Development (TDD), Software Development, Code Architecture, Architecture, Performance Tuning, Testing, Unit Testing, E2E Testing, Clean Code

Senior Engineer

2022 - 2022
Mortgage300 Corporation
  • Reviewed the code of an entire ASP.NET application.
  • Provided a to-do list regarding code security and protection against hacking.
  • Gave suggestions on how to increase the performance of the code.
  • Provided source control-related suggestions such as a branching strategy.
Technologies: C#.NET, C#, Azure, Microsoft SQL Server, Xamarin, Twilio API, Telerik, Web Services, .NET, ASP.NET, ASP.NET Razor, Software Development


2020 - 2022
  • Developed a fee calculation (written in C#, uses Oracle and/or MS SQL database) application for funds based on several business rules. Took part in sprint planning as an architect.
  • Tracked bugs and tasks using Jira. Observed and changed TeamCity builds and releases. Assigned bugs, checked SonarQube stats, and managed the build/deployment chains and pipelines on more than 20 environments.
  • Planned and implemented new features, created documentation of the latest and existing features, and took part in several analyses regarding the used tools, techniques, and technical debts.
  • Collaborated closely with the product owner and business analysts to ensure that the implemented features fulfilled the current business requirements.
  • Worked on developing new product features and client-specific requirements throughout the SDLC.
  • Wrote documentation for new product features and training of junior team members, internal knowledge transfer presentations.
  • Performed code reviews, testing, and QA of new features and bug fixes.
  • Supported in planning across multiple development teams.
  • Worked with the product manager and consultants to clearly define client requirements and translate those business requirements into technical stories that could be worked on by the development team.
  • Provided product support in investigating client issues and provided fixes and workarounds.
Technologies: C#, C#.NET, Oracle, Toad, SQL, Testing, Scrum, Agile, Jira, TeamCity, SonarQube, Subversion (SVN), Continuous Deployment, Continuous Integration (CI), CI/CD Pipelines, Build Pipelines, E2E Testing, Agile Sprints, DevOps, Agile DevOps, Azure, Visual Studio, Visual Studio Code (VS Code), Databases, XML, SQL Performance, .NET 5, .NET, Architecture, Unit Testing, NUnit, Microsoft Unit Tests, Software Development, Code Architecture, Performance Tuning, Clean Code, Banking & Finance, Leadership, Team Leadership

Windows Agent C# Developer

2021 - 2021
Stairwell, Inc.
  • Developed a Windows service to detect binary file changes and send the suspicious changes to a remote virus scanner.
  • Received various file changed (moved, created, and renamed) event notifications from a Windows Kernel driver with the help of Interop.
  • Checked the real file type based on the byte signature of the changed files.
  • Created a WIX installer for the project to add, remove or update the service and to set some initial parameters.
  • Stored the encrypted list of scanned items locally as well.
  • Implemented Nunit tests and a console application for testing.
Technologies: C#, Windows, Wix, Encryption, Windows Services, NUnit, COM Interop, .NET, ASP.NET, .NET Core, Software Development, Unit Testing, Clean Code

Senior .NET Engineer

2021 - 2021
Annalise AI Pty Ltd
  • Implemented a windows service to keep the communication alive between the Annalise Agent (custom code which runs always) and the main UI application.
  • Created an auto-restart and auto-upgrade feature for the service.
  • Developed some minor additional features (heartbeat and security) for the service.
Technologies: .NET, Windows Communication Foundation (WCF), Amazon Web Services (AWS), JavaScript, Web Services, ASP.NET, ASP.NET Razor, Software Development


2020 - 2020
Freelance (Smaller Projects)
  • Ported a legacy VB6 application to Windows 7 GUI/OCX/DLL.
  • Created a C# application to interact with other GUI applications through WCF calls and duplex WCF proxies.
  • Developed an AWS Lambda function for user authentication, key encryption, and custom logic with Python 3.
Technologies: Amazon Web Services (AWS), Python 3, VB, VB.NET, WCF Web Services, Encryption, Decompilation, Git, GitHub, DevOps, REST APIs, REST, MVC Razor, C#, C#.NET, JavaScript, Web Services, .NET, Software Development

Assistant Director | Senior Software Developer | Engineer

2017 - 2020
  • Planned, implemented, maintained, and fixed the rules and core functionalities of a multi-shore tax reporting application with more than 400 calculation rules and a distributed architecture with more than 100 parallel calculation threads.
  • Managed and maintained the Docker environment and web UIs based on Razor and Angular.
  • Maintained the infrastructure and the Windows and SQL server by implementing health monitoring and cleanup processes and optimizing resource usage.
  • Designed web services and generated corresponding classes based on the XSD. Loaded XML data with LINQ to XML.
  • Preparing and doing source code and TFS migration to Azure DevOps.
  • Planned architecture (partially as a lead architect) and development of a tax reporting application based on bank data.
  • Cleaned complex data and worked on imported (ETL), calculations, and PDF formats.
  • Gathered user requirements and consulted with BAs and users, while coaching two other developers and several BAs.
  • Performed automatic end-to-end tests as a part of CI/CD, multiple weekly releases to three environments and seven servers, and Windows server setup planning.
  • Optimized performance based on the results of the automatic end-to-end tests.
Technologies: API Integration, Fintech, Full-stack, Regression Testing, Best Practices, MVC Razor, ASP.NET, ASP.NET MVC, APIs, .NET, Server Infrastructure, .NET Core, Load Testing, App Infrastructure, Code Architecture, Requirements Analysis, Data Loading, Microsoft SQL Server, Parallel Programming, Kanban, Scrum, Docker, Angular, C#.NET, Azure, jQuery, JavaScript, HTML5, CSS3, Bootstrap UI, Architecture, Bug Fixes, Git, GitHub, DevOps, C#, Continuous Integration (CI), Continuous Deployment, HTML, Databases, XML, Agile, Sprints, Agile Sprints, Visual Studio, Visual Studio Code (VS Code), Azure DevOps, XSD, LINQ to XML, Web Services, SQL Performance, Test-driven Development (TDD), Software Development, Performance Tuning, Testing, Unit Testing, E2E Testing, Clean Code, Banking & Finance, Leadership

Associate Director

2016 - 2017
  • Planned out the architecture, development, change management, code reviews, and bug fixes of an internal business application with a web app, ClickOnce, and Windows service components.
  • Worked on complex business functions, forecasting, nightly calculations, and client report generation regarding the performance of several financial organizations based on the data provided by them.
  • Continuously communicated with the business users which included requirement gathering, release planning, training, coaching, and mentoring of an apprentice.
Technologies: Fintech, Full-stack, SQL Server Integration Services (SSIS), Angular, Regression Testing, Best Practices, WCF Web Services, .NET, Agile, JavaScript, Banking & Finance, Business Reporting, Requirements Analysis, Scrum, Microsoft SQL Server, C#, DevExpress, DevOps, Agile Sprints, Sprints, Visual Studio, Code Architecture, Testing, Unit Testing, Clean Code

Senior BI Architect

2014 - 2016
Infomatix Ltd.
  • Led two Scrum development teams, ensured deadlines were kept and provided technical support for all team members.
  • Extended the TIBCO Spotfire data visualization application with enhancements, extensions, and management tools.
  • Reviewed the code, designed the software architecture, trained, ensured quality, and found and investigated new directions and technologies.
  • Optimized SQL, Hadoop and Hive queries, and C# code resulting in 30-200% performance improvement.
Technologies: API Integration, Fintech, Full-stack, Regression Testing, Best Practices, WCF Web Services, ASP.NET MVC, ASP.NET, jQuery, Web MVC, MVC Razor, APIs, .NET, Quality Assurance (QA), Kanban, Scrum, Jira, Microsoft SQL Server, C#.NET, Financial Reporting, Business Intelligence (BI), Spotfire, Git, GitHub, DevOps, Agile, TFS Work Items, Visual Studio, ASP.NET Web Forms, Web Application Forms, Web Services, Databases, SQL Performance, Software Development, Code Architecture, Architecture, Performance Tuning, Testing, Unit Testing, Clean Code, Banking & Finance, Leadership, Team Leadership

Lead Developer

2013 - 2014
  • Led a team of four developers that designed and built a distributed N-tier architecture multimedia content provider system like Netflix; it was used in multiple countries with multiple languages and had a central management system on 100+ servers.
  • Planned, designed, and developed a distributed web app for a hardware store. The app's main functionalities were to sell custom products to suppliers and generate and print statistics.
  • Optimized SQL queries and C# code, resulting in a 30-50% performance improvement.
  • Consumed third-party web services and used XSD to transform parts of the core data.
Technologies: API Integration, Fintech, Full-stack, Regression Testing, Best Practices, WCF Web Services, APIs, MVC Razor, jQuery UI, ASP.NET MVC 6, ASP.NET, .NET, jQuery, JavaScript, HTML, Microsoft SQL Server, C#.NET, Git, GitHub, DevOps, SQL, Windows, WinDbg, ASP.NET Web Forms, Web App Testing, ASP.NET MVC, XSD, Web Services, ASP.NET Razor, Databases, Software Development, Code Architecture, Architecture, Performance Tuning, Testing, Unit Testing, Clean Code, Leadership, Team Leadership

Senior Software Engineer

2012 - 2013
EPAM Systems
  • Designed and developed multiple internal web apps to support my team's HR and resource planning processes.
  • Took part in the first round of a Google hackathon and created a robot that had to occupy areas based on the rule book.
  • Optimized SQL queries and C# code resulting in 10–80% performance improvement.
Technologies: Full-stack, Best Practices, WCF Web Services, jQuery, ASP.NET Razor, ASP.NET MVC, ASP.NET, .NET, Test-driven Development (TDD), Business Requirements, Requirements Analysis, Scrum, SVG, Oracle, Microsoft SQL Server, JavaScript, MVC Razor, C#.NET, Git, GitHub, Visual Studio, ASP.NET Web Forms, Databases, Agile, Software Development, Testing, Unit Testing, Clean Code

Architect | Planner | Developer

2004 - 2013
  • Developed a complete application for a company with two shops and 25 employees (sellers). The app covered all the needs of the shop. From 2011, it partially integrated with the webshop (both used the same storage).
  • Implemented the main functions of sales, billing, automated orders, storage management, and alerts.
  • Developed various reporting forms, including automated, customizable, and time-focused reports (daily, bi-weekly, monthly, and yearly).
  • Created a business recovery plan which included graceful degradation; also owned performance monitoring.
Technologies: PostgreSQL, MySQL, Databases, SQL Performance, Software Development, Code Architecture, Architecture, Performance Tuning, Testing, Unit Testing, Clean Code, Leadership

Senior Software Developer

2007 - 2012
Grape Solutions Ltd.
  • Planned and implemented the base site engine and web check-in, additional services, and passenger data for Wizzair.com version 1 (2007- 2010, not 100%). The engine was written in 40 hours, based on ASP, XML, XSLT, fully dynamic, and recursive.
  • Organized and developed the new site, which has been live since June 2012, Wizzair.com version 2 (2011-2012). The site was rewritten entirely based on a mandatory third-party DLL library.
  • Developed and planned the validation, processing, and transforming of CSV data and saving it into SQL 2005 with SSIS for an American bank. It loaded 2-4GB every night with the constraint that the old must constantly be accessible during the load.
  • Implemented the Microsoft Access migration to SQL Server, which included planning and creating an SQL Server database and loading data from MS Access into it.
  • Built a web-based insurance agent administration system for agent performance and commission calculation, an approval system with a client-side grid containing dynamically defined calculations.
  • Created the VAT refund system for Singapore customs in airports. The WPF UI contained all VAT-related data with the possibility of approval and denial of the VAT refund by the customs.
  • Optimized SQL databases, queries, and C# code resulting in 20-120% performance improvement for several applications and environments to serve the load, persist data, and resist DDOS attacks.
  • During the projects, I had to create a lot of WREB services and generated several references and classes based on their WSDL and XML.
  • Used XSD-based validation for the received XML data.
Technologies: API Integration, Fintech, Full-stack, WCF Web Services, jQuery, MVC Razor, ASP.NET MVC, ASP.NET, APIs, .NET, DDoS, Outlook Add-ons, Visual Basic for Applications (VBA), Performance Analysis, Optimization, Finance, Microsoft Access, ETL, Scripting, XSLT, XML, SQL Server Reporting Services (SSRS), SQL Server Integration Services (SSIS), OLAP, Windows Presentation Foundation (WPF), Website Performance, Load Testing, Clustering, Dynamic Load Balancing, Aviation, Perl, CSS, HTML, JavaScript, Microsoft SQL Server, C#.NET, XSD, Web Services, ASP.NET Web Forms, Databases, Agile, Software Development, Code Architecture, Architecture, Performance Tuning, Testing, Unit Testing, Clean Code, Banking & Finance

Contract Developer

2001 - 2007
  • Designed and developed a complete radio station site. The site had a complex management page with scheduling and other services.
  • Planned, developed, and tested a modular portal system as an alternative to SharePoint 2003 with a workflow engine.
  • Included features such as document, permission, user, and extension management, and new modules can be loaded anytime without restarting the portal.
  • Integrated different parts of a mobile phone-based payment system using BizTalk.
  • Installed a high availability MS SQL, BizTalk, and IIS cluster with a port logging application for one of the biggest Hungarian banks.
  • Created a system test plan for a newly developed system of a mobile telecommunications company with Mercury TestDirector.
  • Developed a real-time factory controlling system with time-critical response times for a laundry business.
Technologies: Full-stack, jQuery, Regression Testing, Best Practices, WCF Web Services, MVC Razor, ASP.NET MVC, ASP.NET Web Forms, ASP.NET, APIs, .NET, Requirements & Specifications, Load Testing, Requirements Analysis, Waterfall Methodology, Kanban, Scrum, Load Balancers, Orchestration, Integration, Eclipse IDE, Oracle, Clustering, Web Services, ASMX, ASPX, CSS, HTML, JavaScript, C#.NET, Microsoft SQL Server, BizTalk, Databases, Agile, SQL Performance, Software Development, Performance Tuning, Testing, Unit Testing, TestDirector

Software Developer

2000 - 2001
Nextra Hungary Ltd.
  • Planned, created, and tested a product with IE Administration Kit. It could install a modem on Windows, connect to a server, guide the user through the registration, and at the end, download a configuration and configure the modem for web surfing.
  • Created internal Nextra web pages based on SQL Server, Visual Basic, ASP, and HTML.
  • Developed an internal app to support the company processes.
Technologies: Full-stack, APIs, SQL, Internet Explorer Administration Kit (IEAK), Active Server Pages (ASP), Visual Basic 6 (VB6), JavaScript, Excel VBA, Databases, Software Development, Testing, Unit Testing

Fully Recursive Web Engine

With another developer, we made a recursive engine that could build and serve web pages based on a recursive XML declaration with its own nodes, page processing, and building engine, which filled the sites with multilingual content (taken from the disk, session, and SQL server).

The engine could implement a graceful degradation and keep the core functionality even if all the auxiliary components failed. The logic contained a continuous performance monitoring system to detect the bottlenecks and DDOS attacks immediately.

Leading the Back-end Development at an On-demand TV Channel

I was the head of back-end development on an on-demand TV channel with monthly subscription fee. My responsibility was to ensure bug-free and architecturally optimal code and manage the releases twice a week in more than 15 countries on more than 50 serves. Besides being a lead, I took part in the code development on the back-end side and the client side as well—I wrote a client for a set-top box in Javascript. I took part in the weekly planning meetings and the management to have the best roadmap and deliver the highest possible business value from week to week. I was also responsible for the back-end API, which was used by all of the clients (Win Mobile, iOS, Android, and web browsers).

Multi-shore Tax Reporting

A C# and SQL server-based, heavily parallel, distributed application with very complicated calculations on a large amount of data (100,000+ data points/customer) with strong performance expectations (regarding the number of the calculations/hour).

My contributions were the data loading (extract, transform, load), the parallel logic in the business layer, several rules, and performance optimization with remarkable results. I was also responsible for the quality assurance of the imported data and the detection of inconsistencies, missing data points, and everything else.

I took part in the core architecture planning and was the only person responsible for the core application part, forming the basis for the customized app features.

Also, I maintained the (virtual) hardware environment (including the Windows, SQL servers, and Docker). I kept the application stable and alive at any circumstances (because of the strict legal delivery deadlines).

Further, I created an end-to-end testing tool, which was able to compare any parts of the reports and find all the differences, regressions, unforeseen data constellations, and calculation errors with a speed of 3,000+ reports/hour.
1998 - 2002

Bachelor's Degree in International Trade

High School for Foreign Trade & Economics - Budapest, Hungary

1995 - 2000

Master's Degree in Computer Science

Technical University - Budapest, Hungary


AZ-104 Microsoft Certified: Azure Administrator Associate



AZ-305 Microsoft Certified: Azure Solutions Architect Expert



AZ-400 Microsoft Certified: DevOps Engineer Expert


MAY 2021 - MAY 2023

AZ-204 Microsoft Certified: Azure Developer Associate



REST APIs, ASPX, API Development, jQuery UI, jQuery, Twilio API, Entity Framework, NSubstitute


Visual Studio, Git, Jira, Slack, Eclipse IDE, Microsoft Access, Spotfire, GitHub, WinDbg, Toad, TeamCity, SonarQube, Subversion (SVN), Microsoft Unit Tests, Wix, Splunk, Elastic, Cucumber, TestDirector


ASMX, MVC Razor, .NET Core, .NET, ASP.NET, ASP.NET Web Forms, ASP.NET MVC, ASP.NET MVC 6, Razor, Windows Presentation Foundation (WPF), Angular, .NET 5, NUnit, Entity Framework Core, .NET 4, ASP.NET Core, Selenium


SQL, C#.NET, JavaScript, XML, C#, ASP.NET Razor, Excel VBA, HTML, CSS, XSLT, Python 3, VB, VB.NET, HTML5, CSS3, Visual Basic 6 (VB6), Active Server Pages (ASP), Perl, Visual Basic for Applications (VBA), XSD


Scrum, Testing, Unit Testing, Agile, E2E Testing, Best Practices, Continuous Integration (CI), REST, MVC Design, Kanban, Requirements Analysis, Load Testing, Clean Code, Management, DevOps, OLAP, ETL, DDoS, Business Intelligence (BI), Test-driven Development (TDD), Parallel Programming, Continuous Deployment, Azure DevOps, Behavior-driven Development (BDD), Microservices Architecture


Databases, SQL Performance, Microsoft SQL Server, PostgreSQL, MySQL, SQL Server Integration Services (SSIS), SQL Server Reporting Services (SSRS), Oracle 10g, Amazon S3 (AWS S3), Amazon DynamoDB


Windows, Docker, Oracle, Azure, Amazon Web Services (AWS), Xamarin, Telerik, Visual Studio Code (VS Code), OpenShift, Apache Kafka

Industry Expertise

Banking & Finance


Architecture, Software Development, Business Logic, Code Architecture, Performance Tuning, Web Services, Waterfall Methodology, APIs, Regression Testing, Full-stack, Fintech, Bug Fixes, Web MVC, Data Loading, Integration, Requirements & Specifications, High Code Quality, TFS Work Items, Financial Reporting, Website Performance, Scripting, Optimization, Performance Analysis, Quality Assurance (QA), App Infrastructure, Leadership, Team Leadership, Delivery Management, API Integration, Decompilation, Bootstrap UI, Group Management, Server Infrastructure, Infrastructure Monitoring, Internet Explorer Administration Kit (IEAK), BizTalk, Clustering, Orchestration, Load Balancers, Aviation, Dynamic Load Balancing, Finance, Outlook Add-ons, SVG, Business Requirements, Business Reporting, WCF Web Services, Encryption, DevExpress, CI/CD Pipelines, Build Pipelines, Agile Sprints, Agile DevOps, Sprints, Web Application Forms, Web App Testing, LINQ to XML, Windows Communication Foundation (WCF), Windows Services, COM Interop, .NET 6, Argo CD, Google BigQuery, Google Data Studio

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