Hire the Best .NET Core Developers in London, UK

As a .NET developer, I am a skilled software developer who specializes in creating applications using the Microsoft .NET Core. I have a strong understanding of programming concepts and are proficient in languages like C#. My primary role is to design, develop, and maintain applications using the .NET framework. This involves working with various tools and technologies to build desktop, web that run on Windows operating systems and other platforms. I am also adept at working with different software development methodologies such as Agile or Scrum and are able to work collaboratively with other team members, including project managers, designers, and other developers. 🔥 What I specialize in: C# / VB.NET Desktop Application Development (WinForms, DevExpress) SQL Server performance tuning & query optimization ERP & Accounting Systems (Inventory, GST, Reporting) QuickBooks Desktop Integration (QB SDK, automation, sync) Fixing slow applications caused by database or code issues Excel/VBA → .NET Application or DLL Conversion API integrations & system synchronization Auto-updaters (Application + Database migration) Industrial systems (Serial Port, Bluetooth, real-time control) 💡 Proven real-world experience: ✔ Inventory & Billing Systems with DevExpress ✔ Custom CRM & HRM Solutions (Multi-User) ✔ Financial Dashboards with Real-Time Charts ✔ Booking & Scheduling Tools with Reminders ✔ Secure Login & Licensing Applications ✔ ERP system for diamond industry (high-volume transactions) ✔ Optimized SQL performance for business-critical systems ✔ QuickBooks automated order & invoice sync ✔ Bulk email automation system (Google API integration) ✔ Excel VBA converted to scalable VB.NET DLL ✔ API-based auto-update system with database upgrades ✅ Technical Expertise ✔ Languages & Frameworks: C#.NET, VB.NET, WinForms, Desktop Application, .NET Framework, .NET Core ✔ UI Frameworks: DevExpress, Custom Controls ✔ Backend Logic: Complex Business Rules, Data Processing, API Integrations ✔ Databases: SQL Server (Advanced) - [Stored Procedures, Functions, Triggers, Query Optimization, Performance Tuning, Indexing & Execution Plans], Oracle Database, MS Access, Database Design & Architecture, Data Migration & Integration ✔ Extras: Reporting, Printing, Multi-language Apps, Licensing Systems, Crystal Reports / RDLC Reporting, Git Version Control ⚡ Why clients hire me: ✔ 14+ years of strong industry experience ✔ Expert in C#, .NET, and enterprise application development ✔ Strong database optimization and performance tuning skills ✔ Experience in SQL Server, Oracle, and MS Access ✔ Strong experience with real-world business systems (ERP) ✔ I quickly identify performance bottlenecks and fix them ✔ Focus on speed, stability, and long-term scalability

Senior C#, .NET .NET Core, ASP.NET, ASP.NET Core, WPF, React, AI Full Stack Developer I’m a Senior Full Stack Developer with more than 7 years of experience building reliable web applications using C#, .NET 8, .NET Core, ASP.NET Core, ASP.NET Web API, React, and TypeScript. C# and .NET are the technologies I work with most. I’ve spent years building backend systems, SaaS platforms, business applications, internal tools, and API-driven products with C#, .NET Core, and ASP.NET Core. A large part of my work involves building secure and scalable ASP.NET Core Web API applications. I use .NET 8 and C# to develop REST APIs, business logic, background services, authentication systems, third-party integrations, and real-time features. I’m also comfortable working across the full stack. On the frontend, I use React, Next.js, TypeScript, Tailwind CSS, and Blazor. I regularly connect React applications to ASP.NET Core Web API backends and handle everything from database design to deployment. I’ve worked on projects in healthcare, fintech, SaaS, and other data-focused industries. Some projects involved building new C# and .NET Core applications from the ground up, while others required improving existing ASP.NET Core systems, fixing performance issues, adding new Web API endpoints, or modernizing older software. I can help with: C# and .NET 8 application development .NET Core and ASP.NET Core backend development ASP.NET Core Web API design and development REST API and third-party API integrations Entity Framework Core and Dapper SQL Server and PostgreSQL development Authentication, authorization, JWT, and OAuth SignalR and real-time application features Hangfire and background processing React and TypeScript frontend development Full stack SaaS development Legacy .NET application modernization Azure and AWS deployment Docker, Kubernetes, and CI/CD pipelines Over the last two years, I’ve also focused heavily on AI and RAG development. I help companies add practical AI features to existing C#, .NET 8, .NET Core, and ASP.NET Core applications. This includes document search, internal knowledge assistants, AI chatbots, semantic search, automated workflows, and retrieval-augmented generation. I’ve worked with Azure OpenAI, the OpenAI API, embeddings, vector search, Azure AI Search, pgvector, Pinecone, Elasticsearch, and PostgreSQL. For example, I can build an AI-powered ASP.NET Core Web API that processes documents, stores embeddings, retrieves relevant information, and sends the right context to an LLM. I can then connect that service to a React or TypeScript frontend. My goal is always to build AI features that are useful in real products, not just impressive demos. I also help clients modernize older .NET applications. That may involve moving from .NET Framework to .NET Core, upgrading an existing system to .NET 8, replacing an outdated ASP.NET application with ASP.NET Core, improving old Web API services, or rebuilding a WinForms or WPF application as a modern web platform. I understand that legacy systems often support important business operations, so I approach modernization carefully. I focus on improving the system without creating unnecessary risk or disrupting existing users. When building new systems, I care about clean architecture, readable C# code, sensible database design, clear API contracts, and maintainable frontend components. I don’t believe in making software more complicated than it needs to be. I prefer practical solutions that are easy to understand, test, maintain, and extend. My main technical stack includes: C#, .NET 8, .NET Core, ASP.NET Core, ASP.NET Core Web API, Entity Framework Core, Dapper, LINQ, SignalR, Hangfire, FluentValidation, SQL Server, PostgreSQL, Redis, Elasticsearch, React, Next.js, TypeScript, JavaScript, Tailwind CSS, Blazor, Azure, AWS, Docker, Kubernetes, Azure DevOps, GitHub Actions, xUnit, Serilog, and Seq. Clients usually value my clear communication, realistic estimates, and ability to take ownership of a feature from start to finish. I’m comfortable joining an existing C# and .NET team, maintaining a large .NET Core codebase, building a new .NET 8 application, developing an ASP.NET Core Web API, or handling a complete React and .NET full stack project. If you’re looking for a dependable C# developer with strong experience in .NET 8, .NET Core, ASP.NET Core, Web API, React, and AI integration, I’d be happy to learn more about your project.

Experienced Web Developer and WordPress Specialist with over 3 years of hands-on experience in designing, developing, and maintaining dynamic websites. Proficient in creating custom WordPress themes and plugins, ensuring seamless user experiences and robust functionality. Committed to delivering high-quality, responsive, and SEO-friendly websites tailored to meet client goals and exceed expectations. Skills and Expertise: WordPress Development: Custom themes, plugins, child themes, and full website setups. Web Design: Responsive design, UI/UX design, and conversion optimization. Front-End Development: HTML5, CSS3, JavaScript, jQuery, Bootstrap. Back-End Development: PHP, ASP.NET, MySQL, database management, API integrations. eCommerce Solutions: WooCommerce setup, customization, payment gateway integration. SEO & Performance Optimization: On-page SEO, website speed optimization, performance tuning. Website Maintenance: Security updates, backup solutions, troubleshooting, and support. Content Management: WordPress CMS management, migration, and site updates. Key Projects: Custom WordPress Website for LUMS UNIVERSITY: Developed a bespoke WordPress site with custom themes and plugins, optimized for SEO, resulting in a 91% increase in organic traffic. E-Commerce Platform for Changa Nursery: Built a fully functional WooCommerce store with custom features, integrated payment solutions, and streamlined checkout processes, boosting sales by 72%. Corporate Website for Handy Man: Created a responsive and visually appealing corporate site that enhanced brand presence and user engagement. Why Choose Me? Client-Focused Approach: I work closely with clients to understand their vision and translate it into functional, visually appealing websites. Quality Assurance: My work is driven by a commitment to quality and attention to detail, ensuring all projects are completed to the highest standard. Reliable Communication: I maintain clear and consistent communication throughout the project lifecycle, ensuring clients are informed and involved. Ongoing Support: I provide comprehensive support and maintenance services to ensure your website remains secure and up-to-date.

I build and improve custom .NET web applications, dashboards, internal tools, admin panels, and client portals using ASP.NET Core, Blazor, React, APIs, and clean backend logic. I can join an existing .NET project, understand the current codebase, fix issues, add new features, improve the frontend/backend, and support the product long-term. My clients typically need one of two things: 1. A new web application, dashboard, admin panel, or client portal built from scratch. 2. A reliable developer to take over and evolve an existing system without breaking what's already working. HOW I HELP: ✅ Build custom .NET web applications for business workflows ✅ Develop dashboards, admin panels, internal tools, and client portals ✅ Improve existing ASP.NET Core / Blazor / React applications ✅ Add new features, fix bugs, and support long-term product development ✅ Integrate APIs, databases, authentication, user roles, and third-party tools ✅ Help businesses replace manual processes with clear, stable, scalable web systems PROBLEMS I SOLVE: ⚠️ Outdated or unstable web applications ⚠️ Internal processes still running on spreadsheets or manual work ⚠️ Existing .NET projects that need bug fixes, new features, or ongoing support ⚠️ Dashboards or admin panels that are hard to use or maintain ⚠️ Business tools that don't scale as the company grows ⚠️ No reliable developer who can understand the codebase and support it long-term WHAT MAKES ME DIFFERENT: Most freelance developers can write code. Fewer can be trusted with an existing, live system. I focus on: ✅ Clean, maintainable backend logic — not quick fixes that create bigger problems later ✅ Understanding the full workflow before building a feature ✅ Clear communication throughout the project ✅ Staying engaged after delivery, not disappearing once the invoice is paid WHAT YOU GET: I build and improve custom .NET web applications designed around your business workflow, not just around a list of technologies. That can mean building a new application from scratch, improving an existing ASP.NET Core / Blazor project, creating a dashboard or admin panel, connecting APIs, fixing bugs, adding features, or providing long-term support. 🎁 INCLUDED WITH EVERY PROJECT: ✅ A high-level review of your current workflow or application structure, with suggestions for improving stability, usability, or maintainability ✅ Suggestions on simplifying features before development starts ✅ A clear breakdown of what to build first, if your project has multiple stages GUARANTEE: If the final result doesn't match the agreed brief, scope, and quality standards, I'll revise it within that same scope until it meets the requirements. MY WORKFLOW: Not sure how to describe the technical task yet? I'll help you structure it. Send me your idea, existing app, requirements, user flow, business process, Figma design, bug list, API docs, or current codebase, and I'll help define the right approach. MY PROCESS: 1. Discovery & requirement review 2. Workflow / codebase understanding 3. Technical planning 4. .NET / ASP.NET Core / Blazor / React development 5. API, database & backend logic implementation 6. Testing, bug fixing & improvements 7. Revisions & final delivery Click the message button, send me your idea, existing app, or technical task, and I'll help you define the next step.

🔸 Top 1% in Upwork. 🔸 100% Job Success. 🔸 4,000+ hours. 🔸25+ years experience. I deliver high-quality, engineered software that is robust, works at scale, and can grow as fast as your business grows. ❝ High-quality software is not complicated - it just requires discipline and steadfast attention to detail on each step of the journey. ❞ What's stopping you from starting your journey to software excellence and fixing your business' pains? You can arrange a call with me to discuss your project needs for free in a 30-minute consultation call! Hi. I'm Jason - an experienced (25+ years) software architect and engineering professional involved in all parts of the SDLC (Waterfall, Agile and Hybrid methodologies). With a wealth of experience across industries such as commercial aviation, banking (real-time payments processing & FX), 24/7/365 manufacturing lines, e-commerce, and public transport (smart card), I will bring a passion for delivering elegant and reliable solutions to your project. I will work with you (and your team) to provide the best possible technical solution to your business problem. No matter the business domain or challenges you are facing, l have deep technical and architectural knowledge, as well as excellent communication skills, to help solve your business problem with the right software solution. I will bring to bear a highly focused set of technical and people skills to help your project succeed. The recommendations and advice I provide focus on minimizing risks and maximizing your project's chances of success. This is what my 25+ years of experience bring you: honest, robust, and intelligent solutions to see you succeed. When asked to build software, I deliver high-quality server-side C# .NET software solutions that give what you need: Software engineered to be robust, scalable, and designed to exceed your business expectations. What you'll get when you choose me to work with you: ⭐️ Clear, effective communication ⭐️ Precise, quality recommendations to ensure success for your project ⭐️ A focused, collaborative approach to work with you and your team ⭐️ A no-nonsense, results-focused approach that delivers value to your project For example, this are what a couple of my clients had to say: ❝Jason is by far the best architect I have ever worked with. He displays extreme ownership of his work and it's incredibly refined. Every deliverable was on time or ahead of time. Not only did Jason provide an incredibly performant and scalable architecture, the documentation he provided was top notch. I will forever keep Jason and my goto for any and all technical and solution architectural needs.❞ Cade - VP Engineering - US Software Company ❝Jason helped get our team on our feet for doing proper documentation and much more, actually. He helped improve the engagement of our team members and how they work together. If we can, we will surely ask for his help again in the future. I can only give high praise of Jason's quality of work. We highly recommended for documentation and general architectural design work.❞ Alexander L - Acting CTO - Global On Media If you are interested in working together, please invite me to your job on Upwork. I look forward to hearing from you soon and helping you deliver on your software vision. Regards, Jason. A highlight of my technical specialties I can help you with: ✅ .NET Technical and Solution architecture consultancy and design ✅ C#.NET ✅ Team leading, technical .NET mentoring, and coaching ✅ High availability solution designs (24/7/365) ✅ Event-driven architectures (including actor-based systems) ✅ Highly concurrent software design (thread-safe) ✅ High volume, low latency software designs ✅ Cloud (MS Azure and AWS) solutions ✅ Hybrid (on-premise and Cloud) solutions ✅ Microservices ✅ Message brokers and ESB ✅ SOLID, DDD, OOP, and TDD ✅ Experienced in Agile and Hybrid delivery models ✅ Container (Docker) deployments software using CI/CD (Azure Devops) ✅ Dependency Injection (DI using Autofac, DryIoc) A highlight of the software products I'm experienced with: ✅ Sparx Enterprise Architect ✅ JetBrains Rider IDE ✅ Confluence, JIRA ✅ Git ✅ Resharper, DotMemory, DotTrace ✅ VMWare (Fusion) ✅ Visual Studio 2019 IDE Other clients had this to say about my work with them: ❝Jason was a tremendous professional, outstanding architectural skills and understanding both technical and business requirements.❞ Brian V - COO - LaunchControl

Looking for a .NET full-stack developer who can own both the C# backend and the frontend without handing you two contractors to coordinate? I have spent fifteen-plus years building C#, ASP.NET Core, and Azure applications end to end - from the API and data layer through to the React frontend - across smart city IoT, fintech, and SaaS. ✅ .NET full-stack developer, 15+ years on C#, ASP.NET Core, and Azure ✅ One Upwork engagement to date, a Web API build, closed at a full 5.0 of 5 over 130 logged hours ✅ Senior engineer and architect at Euristiq, an AWS Advanced Tier partner ✅ Full-stack .NET - ASP.NET Core APIs, React frontends, and event-driven backends on Azure ━━━━━━━━━━━━━━━━━━━━━━━━ 🔷 What I Do as Your .NET Full-Stack Developer I build .NET applications end to end: C# and ASP.NET Core on the backend, React on the frontend, and a data layer designed for load underneath. Owning both sides means the API contract and the UI move together, without the gaps that show up when a separate backend and frontend team hand off to each other. Whether you need a new .NET product built from scratch, a legacy .NET application modernized, a monolith broken into services, or a React frontend wired onto an ASP.NET Core API, I bring senior structural thinking and a clean handover to every project. 🔷 Core .NET Full-Stack Services ▸ .NET backend development - C# and ASP.NET Core REST APIs, background and hosted services ▸ React frontends wired onto ASP.NET Core APIs, with clean, versioned contracts ▸ Legacy .NET modernization and monolith-to-microservices migration ▸ Cloud migration to Azure and AWS - re-platform, re-architect, lift-and-shift ▸ Distributed .NET systems - event-driven design over RabbitMQ, MassTransit, Azure Service Bus ▸ Azure cloud applications - Service Bus, Event Hubs, Functions, IoT Hub, Application Insights ▸ Microservices architecture, saga orchestration, and API design ▸ Data layer design - MS SQL Server, MongoDB, Redis, Entity Framework ▸ Software architecture consulting on system and migration design 🔷 Where I Have Shipped It At Euristiq, an AWS Advanced Tier partner, I have spent years engineering and architecting .NET applications for enterprise and product clients - ASP.NET Core on Azure, React frontends, event-driven microservices with RabbitMQ and MassTransit, and backends handling device ingestion and telemetry. Before Euristiq I led backend delivery at Mindworks on a city-scale smart lighting platform and a public bike-sharing backend, both built in .NET on MS SQL with MongoDB and Redis. On Upwork, a Web API backend build closed at a full 5.0 of 5 across 130 logged hours. These have been long-running engagements measured in hundreds of hours rather than one-off tasks, with the code handed over clean enough for an in-house team to own and extend. 🔷 Who I Work With I am the right fit for teams who want one senior person to own a .NET product end to end: a startup that needs a full application built, a company modernizing a legacy .NET system, or a product team that needs both the API and the UI moved forward by someone who has made the structural calls before. I am not the right fit for a quick script or a one-file change; that work is better and cheaper with someone else. 🔷 My Engineering Process Send me a description of your product and within 24 hours I will tell you whether the approach makes sense for your scale, before any contract is signed. From there: a written design covering the API, data layer, and frontend structure; then implementation in C#, ASP.NET Core, and React with observability built in; then a clean handover. I leave behind .NET applications your engineers can read, extend, and run without me. 🛠 Tech Stack ⚡ C#, ASP.NET Core, .NET Core, .NET Framework ⚡ React, JavaScript, ASP.NET MVC, REST APIs ⚡ Azure Service Bus, Event Hubs, Functions, IoT Hub ⚡ RabbitMQ, MassTransit, SignalR ⚡ MS SQL Server, MongoDB, Redis, Entity Framework, Docker ━━━━━━━━━━━━━━━━━━━━━━━━ If you need a .NET full-stack developer who owns both the backend and the frontend and hands over a product your team can run, send me a message. Happy to review your current .NET application or jump on a call to scope the work.