Full Stack Engineer

a leading German tech startup revolutionizing after-sales processes in car dealerships, is looking for a Full Stack Engineer (m/f/d) to join our growing development hub in Valencia., We are looking for a skilled and adaptable Full Stack Engineer to strengthen our development team. You will work across a production-grade Node.js backend, a React + TypeScript frontend, and the data and AI integrations that connect them. You will report to the Technical Lead and operate with a high degree of autonomy. We value engineers who take ownership of features end-to-end - from database schema design to deployed UI - without requiring close supervision. This is not a traditional frontend role. You will regularly work on backend services, job queues, database migrations, authentication flows, and AI-driven features. CORE RESPONSIBILITIES * Develop and maintain web application features across the full stack (React + TypeScript frontend, Express.js + TypeScript backend) * Design and implement database schemas, migrations, and optimized queries (MySQL / MariaDB) * Build and maintain REST APIs and integrate them with frontend systems * Work with background job processing, scheduled tasks, and asynchronous workflows

• Contribute to AI-driven features, LLM integrations, and prompt engineering

Integrate web applications with data platforms (PowerBI, Databricks, Azure Data Lake Storage)

• Ensure scalable, secure, and production-ready implementations

Maintain high test coverage and participate in code reviews * Monitor and debug production systems independently * Collaborate with technical and business stakeholders REQUIRED TECHNICAL SKILLS Frontend & Web * Strong expertise in React + TypeScript * Advanced HTML5 / CSS3 (Bootstrap, Tailwind CSS) * REST API design and consumption * Git version control Backend & Infrastructure * Solid experience with Node.js + Express.js * MySQL / MariaDB - schema design, query optimization, connection pooling, migrations * Redis - caching, job queues, distributed locking * Background job processing (BullMQ or similar queue systems) * Docker - containerization, multi-stage builds, Docker Compose

JWT authentication and role-based access control

• Scheduled task management (cron jobs) Data & Cloud

• Practical experience with Databricks and Azure Data Lake Storage (ADLS)

Understanding of data pipelines and structured/unstructured data handling * Experience integrating web applications with data platforms (PowerBI, Databricks, ADLS) * Familiarity with Azure services (Azure AD, Static Web Apps, or similar) * Understanding of data synchronization pipelines and ETL processes AI & Prompt Engineering * Understanding of AI-driven applications and LLM integrations

• Ability to design, test, and refine prompts for reliable AI outputs

Experience working with AI APIs (OpenAI, Azure AI, Anthropic, etc.) Code Quality & Security * Writing and maintaining unit tests (Jest, Supertest) * Maintaining high test coverage standards (95%+ preferred)

• Input validation and schema enforcement (Joi or similar)

Awareness of OWASP Top 10, rate limiting, CORS, and secure authentication flows NICE TO HAVE * PowerBI API integration and DAX queries * E2E testing frameworks (Cypress, Playwright) * PDF generation pipelines (pdf-lib, Puppeteer)

• Email automation systems (Nodemailer, templated dispatch)
• Prometheus / Grafana monitoring

Azure Static Web Apps or similar deployment platforms * CI/CD pipeline configuration

• Experience with scalable cloud architecture (Azure preferred)

• UI/UX design awareness SOFT SKILLS

• High ownership mentality - you treat features as yours from start to finish

Professional and structured communication * Strong problem-solving ability * AI-adaptive mindset - comfortable working with rapidly evolving technologies * Team-oriented but capable of independent execution, Professional experience of at least 3 years (mandatory)

At NUMBERO, our mission is to equip car dealerships with cutting-edge tools to optimize their after-sales operations. We integrate trusted sources for parts and labor costs, various Dealer Management Systems, and other relevant data sources. We also leverage metadata analysis to drive intelligent insights. Headquartered in Germany and supported by a growing international team, we focus on innovation, collaboration, and delivering outstanding value to our clients. Our Valencia office plays a key role in shaping the future of our technologies and services., Still reading? Great! Ready to become part of our mission? As we are looking for someone with a good drive, our hard skill requirements are not too strict. What really matters to us is that you bring your own drive and are eager to make a difference. Send your CV to ****** with the subject line "Full Stack Engineer". We look forward to meet you!