Full-Stack Software Engineer (React, NextJS) - Freelance (M/F)

About the role

Daily rate (TJM): €470/day CONTEXT Our SaaS platform is in a key phase of acceleration and consolidation. In order to double our delivery capacity and ensure the stability of the application before it scales, we are strengthening the technical team. You will work in pairs with the existing developer to integrate new business modules, deploy our behavioral tracking tools, and automate quality control of the data displayed to users. MISSIONS * Co-develop and integrate API and UI components for our performance monitoring, pricing analysis, and commercial management modules. * Third-party integration & observability: implement the Medallia SDK for collecting user feedback. * Set up application observability, performance monitoring, and behavioral analysis tools. * Develop control mechanisms to ensure the consistency and reliability of metrics transmitted by the API and displayed on the UI interface. * Automate validation processes (visual regression tests, E2E tests) to detect anomalies upstream and ensure the sustainability of the platform. TECHNICAL SKILLS * Full-Stack: solid experience in creating/consuming APIs (REST) with a back-end language (e.g., Python) and mastery of a modern front-end framework (e.g., React, NextJS). * Monitoring & tracking: experience in integrating third-party SDKs (e.g., Datadog, Clarity, Medallia, or equivalents). * Quality & testing: mastery of testing practices (E2E, integration) and CI/CD automation. BEHAVIORAL SKILLS * Team spirit: work in a fluid pair with the existing developer (code reviews, pair programming, technical alignment). * Product culture: work hand-in-hand with the Product Manager to transform functional needs into reliable components. * Pragmatism: ability to deliver quickly while maintaining clean and maintainable code. * Proactivity: ability to take initiatives and propose adapted solutions. * AI-Augmented Mindset: daily use of AI assistance tools to accelerate development and optimize code quality. * Languages: professional English required (written and spoken). WORKING CONDITIONS * Location: Lille * TJM: €470 1. Solid experience in creating/consuming REST APIs with a back-end language (e.g., Python) 2. Mastery of a modern front-end framework (e.g., React, NextJS) 3. Experience in integrating third-party SDKs (e.g., Datadog, Clarity, Medallia, or equivalents) 4. Mastery of testing practices (E2E, integration) and CI/CD automation 5. Team spirit: pair work, code reviews, pair programming, technical alignment 6. Product culture: collaboration with the Product Manager to transform functional needs into reliable components 7. Pragmatism: ability to quickly deliver clean and maintainable code 8. Proactivity: taking initiatives and proposing adapted solutions 9. Daily use of AI assistance tools to accelerate development and optimize code quality 10. Professional English required (written and spoken)