Full Stack Engineer (Python / React)

Nucleus is seeking a Full Stack Engineer with deep expertise in Python and React to build production-ready systems and harness engineering infrastructure. The role combines user-facing feature development with building the tooling, automation, testing frameworks, and orchestration layers that enable systems, agents, and workflows to run reliably at scale.

• Build and maintain full stack applications using Python backend and React frontend
• Design and implement APIs, services, and orchestration layers for product workflows and internal tools
• Develop harnesses for testing, simulation, validation, execution, and monitoring of complex workflows and agents
• Create reusable frameworks for workflow execution, automated test runs, sandboxed environments, synthetic data generation, scenario replay, and regression validation
• Build developer-facing tools to improve engineering velocity, quality, and repeatability
• Integrate external services, APIs, and third-party tools into internal platforms
• Implement logging, tracing, observability, and error-handling across systems
• Collaborate with product, design, and platform teams to turn business needs into scalable solutions
• Help define engineering standards for reliability, maintainability, and deployment readiness

• Strong hands-on production experience building systems with Python
• Strong hands-on experience building modern frontend applications with React
• Experience designing and consuming REST APIs and async service architectures
• Experience with harness engineering including building tooling for testing, validation, simulation, and execution environments
• Comfortable working across application code and engineering infrastructure/tooling
• Strong understanding of software design, debugging, and performance optimization
• Experience with databases such as PostgreSQL or MySQL
• Familiarity with CI/CD pipelines, Git-based workflows, and deployment practices
• Ability to work independently, move quickly, and make sound engineering tradeoffs
• Preferred: Workflow orchestration, agent-based systems, Docker, cloud infrastructure, background job systems, queues, event-driven architectures, internal platforms, QA tooling, LLM/AI workflow orchestration, observability tools

No specific schedule, location, or benefits information provided in the posting.