Top C# Jobs in St. Louis, MO

Design and develop scalable C++ software for endpoint state and control across Windows, macOS, and potentially Linux. Build reliable, multi-process systems that enforce endpoint behavior, manage local state, support IPC, and operate across millions of devices. Responsibilities include implementing features, improving platform performance, writing design documents, defining architecture and IPC contracts, and making technical decisions in an evolving, sparsely documented environment.

Develop and test systems-level C++ software that defines and enforces endpoint behavior. Initially, the engineer will own testing infrastructure and coverage for two active projects, then contribute to feature development. The role requires strong C++ fundamentals, automated testing experience, and interest in operating-system concepts such as processes, file systems, services, and APIs. Work includes learning unfamiliar systems, collaborating effectively, and supporting reliable endpoint security and management capabilities.

Develop and architect a cross-platform C++ endpoint patching agent for Windows, macOS, and Linux. Responsibilities include code reviews, mentoring engineers, improving development processes, collaborating across patching teams, and translating product needs into resilient technical designs. The role involves system-level APIs, patch installation and rollback logic, embedded databases, and client-server integration.

Design, develop, and field high-performance Ground Control Station and C2 software using C++/Qt/QML and QGroundControl. Lead architecture and technical direction, mentor engineers, define APIs/ICDs, debug integration/latency issues, support field tests, implement post-mission debrief tools, and ensure interoperability with C2 standards.

Develop and modernize enterprise applications using C#/.NET and PostgreSQL, including refactoring a Microsoft Access/VBA application. Responsibilities include writing maintainable code, participating in code reviews, testing, documentation, deployment, and collaborating with the software development team in a fully remote environment.

Lead modernization of a 30-year-old Store Management System by reverse engineering EZC file-based platforms, migrating data and applications to PostgreSQL, and developing enterprise C/C++ software. Responsibilities include architecture, systems integration, APIs, ETL, performance optimization, troubleshooting, documentation, and maintaining business continuity. The role also applies AI-assisted development tools for code analysis, documentation, testing, and modernization while mentoring teams and supporting legacy and modern environments.

Design, develop, test, document, deploy, and support scalable full-stack applications using React, C#/.NET, and Hack. Build backend services, APIs, integrations, and AI-enabled capabilities including LLM workflows. Participate in Agile planning, code reviews, troubleshooting, client communication, and software delivery while applying modern architecture, DevOps, CI/CD, and automated testing practices.

Build and validate reinforcement-learning tasks for AI agents exploring unfamiliar C repositories. Responsibilities include investigating runtime behavior, rewriting engineering questions, refining rubrics and foils, running validation workflows, documenting solutions, and addressing expert review. Work focuses on production systems such as PostgreSQL, Redis, OpenSSH, OpenSSL, and other foundational C codebases.

Leads hands-on full-stack development across architecture, implementation, testing, deployment, and support. Designs secure, scalable C#/.NET and Angular applications, cloud integrations, APIs, and data solutions on AWS. Guides developers, establishes engineering standards, manages CI/CD and automated testing, troubleshoots complex issues, and drives cloud optimization, security, and technical debt reduction. Collaborates with product, architecture, DevOps, analytics, and project teams while supporting migration of on-premises applications to AWS.

Lead a development team while remaining hands-on in full-stack engineering. Design, build, test, deploy, and support secure web applications using C#/.NET, Angular, databases, and AWS. Drive cloud migrations, architecture, CI/CD automation, application security, troubleshooting, performance and cost optimization. Mentor developers, establish engineering standards, lead technical delivery, and collaborate with product, data, DevOps, and architecture teams.

Design, implement, test, and modernize backend services and integrations (TypeScript/Node.js and C++). Lead large projects, write technical specifications and API contracts, enforce coding standards, coach engineers, and drive legacy-to-modern migrations within online banking and core systems.

Architects, develops, and maintains high-performance C++ applications with advanced memory management and multithreaded architectures. Owns critical system components, build systems, CI/CD pipelines, containerization, debugging, profiling, and performance tuning. Leads code reviews, technical planning, and system design while mentoring engineers. Works in Linux environments with Python, shell scripting, SQL, and Git, and collaborates across teams to improve reliability, scalability, and technical growth.

Lead end-to-end development of secure, scalable web applications and data solutions supporting clinical trial operations. Design frontend and backend components using C#/.NET, Angular, AWS, and relational or non-relational databases. Guide architecture, testing, deployment, CI/CD, security, cloud optimization, and regulatory compliance. Mentor developers, oversee technical delivery, troubleshoot complex issues, and lead migration and modernization of on-premises applications to AWS.

Develop and maintain backend services and RESTful APIs using C# and .NET. Design and optimize MySQL schemas and queries, troubleshoot production and staging issues, improve performance and scalability, document architecture, and uphold code quality and security. Collaborate with cross-functional teams in a fully remote environment while contributing to development best practices and continuous improvement.

The C# Developer will design, develop, and support IT solutions using various technologies, ensuring feasibility and leading project initiatives during the software development life cycle.

The Senior Programmer Analyst will develop systems, code and document programs, assist with system design, and improve IT processes and techniques.

The Junior C# Developer will assist in developing system designs, coding, testing, and documenting programs under supervision, while suggesting process improvements.

As a Web Developer, you'll collaborate in a Scrum/Agile team to design and develop web applications using C#, .NET, HTML, and JavaScript, among others.

Develop and optimize high-throughput, low-latency C++ applications for performance and reliability. Responsibilities include identifying bottlenecks and bugs, refactoring code, conducting peer reviews, developing automated tests, debugging multithreaded systems, and collaborating with QA, Operations, architects, product owners, and cross-functional teams to resolve performance issues.

Contribute to high-performance, real-time applications processing critical financial data. Collaborate with teams, develop clean applications, and maintain testing strategies.

Lead and implement observability strategy for Real‑Time Collections, perform hands‑on low‑latency C++ work, embed observability practices across SDLC, define SLIs/SLOs and dashboards, establish GitOps/API-driven observability workflows, and influence platform architecture and reliability.

Evaluate AI coding-agent interactions for usefulness, correctness, engineering judgment, reasoning quality, and developer trust. Provide clear, opinionated feedback, distinguish response-quality levels, and help define standards for excellent interactions with tools such as OpenAI Codex, Claude Code, and Cursor. This contract role requires staff- or principal-level software engineering experience and familiarity with modern AI-assisted development workflows.

Design and implement complex low latency, high throughput software for financial data distribution, conduct testing, and improve software reliability.

The C# / .NET Developer will design and maintain middleware applications, build Shopify integrations, and support a mobile app backend in a remote work environment.

Design and evaluate performance engineering tasks for AI training/evaluation. Optimize runtime, compilers, memory, CPU/GPU and concurrency. Produce documented solutions, evaluate AI-generated code, and build evaluation frameworks and scoring rubrics while collaborating with researchers and SMEs.