Senior Full-Stack Engineer

Senior Full-Stack Engineer Why Sintra? 50,000+ small business owners use Sintra every day. Not because it's another SaaS tool — but because our AI helpers actually feel like teammates. They reply to customers, post on social media, analyze data, and much more. For someone running a business alone, this is the first time they've had help that actually helps. We've built something people care about. Now we need to make it great. Quick summary: We're looking for a full-stack engineer who can own features end-to-end. You'll build tooling for LLMs, implement the frontend for users to collaborate with AI, and create the backend logic that makes it all reliable. The challenge: creating foolproof logic that AI can use autonomously while keeping the frontend simple for non-technical users. You'll ship clean code across the entire stack - Python/Node services, React interfaces, background jobs. Who we're looking for - 4+ years shipping production full-stack applications. - Strong Python, Node.js, and React skills with focus on clean architecture. - Experience with LLM tool calling, function definitions, and prompt engineering. - Solid product thinking - you understand how technical decisions affect user experience. - Comfortable navigating large codebases and understanding service boundaries. - Track record of shipping independently while collaborating well with designers and other engineers. - Strong code review skills - you catch bugs before they hit production. - Comfortable using AI tools to accelerate development. ‍ What you'll do - Create tools/functions that LLMs can reliably call - with bulletproof error handling and clear documentation. - Implement the UI for these tools, working with designers to keep it simple for non-technical users. - Build retry logic, fallbacks, and self-correction mechanisms. - Instrument everything - add tracking and logging to measure real impact. Iterate relentlessly based on data. - Develop background workflows that chain multiple operations together. - Collaborate with designers on technical constraints and possibilities. - Mentor teammates and raise the engineering bar through code reviews and pair programming. ‍ Our tech stack - Frontend: React - Backend: Python with FastAPI (core), Node (microservices) - Infrastructure: Railway, AWS, multiple LLM providers - DevOps & Tooling: Github Actions, Grafana ‍ Salary range: €5,000-8,000/month gross, depending on experience. Benefits - Equity package: share in the company’s long-term success through an equity plan that rewards your impact and commitment. - Flexible working model: enjoy a flexible approach to work that supports a healthy balance between your professional and personal life. - Private health insurance: comprehensive private health coverage to support your well-being. - Workout sessions with a personal trainer: access guided workout sessions with a personal trainer to help you stay active, healthy, and motivated. - Daily office-provided lunch: fresh, complimentary lunch provided in the office every workday to keep you energized and focused. By submitting your application you confirm that you have read and understood our Privacy Notice for Job Candidates: https://bit.ly/4b9hhlE