Dmytro S.

💻 Expert 11+ years of commercial experience as Full Stack Developer 💻 I have a reliable team that is helping me to fill any role that is needed on a project. Any level of expertise, any budget Need a senior ASP.NET Core developer to maintain and extend an existing application? I'm a C# .NET Developer who has taken over 9 existing codebases on ASP.NET Core, ASP.NET MVC and ASP.NET Web API, the oldest a legacy Classic ASP one from 2008, and I fix bugs and ship new features without stopping production. 13 of my 14 Upwork reviews are 5 stars, and 98% of my milestones landed on or before the agreed date. What I do hands-on and independently as a C# .NET Developer: - Migrate .NET Framework, ASP.NET MVC and ASP.NET Web API applications to ASP.NET Core with zero downtime, one area at a time behind the same URLs - Build RESTful API endpoints on ASP.NET Web API and ASP.NET Core Web API, 250+ so far, and secure REST API access with OAuth 2.0 and JWT authentication - API Integration with third-party payment, carrier and CRM systems, webhooks and background jobs included: 35+ integrations - Deploy to Azure App Service, Azure Functions and Azure SQL through Azure DevOps CI/CD for reliable releases: 20+ pipelines, release time from 4 hours to 25 minutes, deployment incidents from 2 a month to 0 over a year - Event-driven microservices on MassTransit and RabbitMQ: 14 services, 1.2M+ messages a day, 0 lost transactions across 4 databases - Clean, maintainable C# with unit tests, 80%+ coverage on my last 3 projects, code review on pull requests, documentation and a runbook at handover - AI coding tools in daily use, every change tested before it ships The data side comes with the C# .NET Developer role: Microsoft SQL Server and T-SQL, 1,200+ stored procedures, Entity Framework and Entity Framework Core, databases up to 600 GB and 900M rows, 40+ slow queries brought under 1s through query optimization. On an existing ASP.NET MVC application I improved performance 30-80%: the heaviest report page from 3.4s to 0.7s, API p95 from 900ms to 180ms, SQL Server CPU down 45%. The front end is mine too: Angular, React, TypeScript, JavaScript, jQuery, Razor views, HTML5 and Bootstrap, 4 SPAs and 300+ UI components, Blazor where the client already uses it. Web development on the whole .NET Stack means one C# .NET Developer answers for a feature from the SQL table to the button. As the incoming C# .NET Developer I start with troubleshooting production: I've found the root cause of 60+ issues nobody else could reproduce, among them an Entity Framework leak that doubled memory every 40 minutes and a real-time message loss above 6,000 connections. I host ASP.NET Core and ASP.NET Web API apps on IIS, Docker and Azure App Service with Service Bus and Application Insights monitoring, load testing to 5,000 concurrent users and 99.95% uptime, Microsoft Azure spend cut 30%, and 5 security pen-test cycles closed with 0 critical findings. PROJECTS 1. SaaS business management platform for 1,200+ businesses: moved ASP.NET MVC to ASP.NET Core over 14 months with zero downtime, real-time messaging scaled out to 8,000+ concurrent users, 50,000+ messages a day. 2. Healthcare portal for a US clinic network, taken over from an agency: Team Lead for 11 people, 120+ bugs closed in 3 months, slowest queries from 18s to under 1s, nightly batch from 5 hours to 40 minutes. 3. Commodity trading portal on ASP.NET Core and Angular: designed the architecture, 600+ pull requests reviewed, 0 lost transactions in 18 months, order book page from 2.1s to 300ms. 4. Warehouse logistics for 3 distribution centres: ASP.NET MVC, ASP.NET Web API and React for 3 years, 400+ truck drivers, SQL Server over 300M+ rows, 99.9% uptime, dock assignment time cut 40%. 5. Enterprise feedback system: .NET Core microservices built from scratch in 12 months for 25,000+ employees in 40 countries, on time and 8% under budget. 6. Social network for car drivers on ASP.NET MVC and ASP.NET Web API: 45,000+ drivers, 1M+ notifications a month, the code still in production 7 years later. I'm Top Rated on Upwork as a C# .NET Developer across 32 jobs with 5 long-term clients, the longest running 4 years. Certified MCSD and Microsoft Exam 486, fluent English and clear written communication, 6+ hours overlap with US and EU time. Anything outside .NET, such as UI UX design, mobile, Python or PHP, goes to the right person on my team under my supervision. If your ASP.NET Core, ASP.NET MVC or ASP.NET Web API application needs a senior C# .NET Developer, send me the repository and a list of what hurts most. You get an answer within 1 business hour and an estimate in 24 hours