Senior Full-Stack Developer

CGS; Paris; Hybride; EUR 85 000 - 120 000; Plein temps

Avantages offerts par ce poste

Health insurance

Daily meal vouchers

Commuting support

Modern Paris offices

Résumé du poste

CGS in Paris seeks a Senior Full-Stack Developer to join a small team of engineers. You will work across backend, data processing and frontend, building a data-intensive, API-driven platform using .NET 9, Python, React and Next.js.

You’ll design scalable architectures, optimise APIs and contribute to CI/CD in a hands-on, collaborative environment. The role offers a hybrid model with modern Paris offices and a competitive package.

Qualifications

• 5+ years of full-stack development experience across frontend and backend.
• Strong proficiency with C#/.NET and Python (FastAPI a plus).
• Experience designing APIs and working with data-intensive apps.

Responsabilités

• Design and develop backend services using C#, ASP.NET Core and EF Core.
• Build Python-based APIs and data pipelines with FastAPI and Pandas.
• Develop frontend interfaces with React, Next.js and TypeScript.
• Design scalable architectures and optimise API performance.
• Work with PostgreSQL and data-heavy applications.
• Contribute to CI/CD and Docker-based development.

Connaissances

C# / .NET

Python

React

TypeScript

APIs design

Outils

Docker

OpenTelemetry

Grafana

PostgreSQL

Description du poste

Build software for the energy transition

Our client is a fast-growing EnergyTech company developing software that helps renewable energy producers manage increasingly complex energy contracts and portfolios across European electricity markets.

As renewable generation continues to grow, energy markets are becoming more sophisticated. Our client is building technology that enables renewable energy producers to model, monitor and optimise their contracts and portfolios, helping accelerate the transition towards market-based energy revenues. We are looking for a Senior Full-Stack Developer to join a team of three experienced engineers and help build and scale this data-intensive, API-driven platform.

The role

This is a genuinely full-stack position, with a balanced focus across backend development, data processing and frontend engineering.

You will work with modern technologies including .NET 9, Python, React and Next.js, contributing to both new product development and the continuous improvement of the existing platform.

Your responsibilities

• Design and develop backend services using C#, ASP.NET Core and EF Core.
• Build Python-based APIs and data processing workflows using FastAPI and Pandas.
• Develop modern web interfaces using React, Next.js and TypeScript.
• Design and maintain reliable, scalable and clean software architectures.
• Optimise API performance and data processing across the platform.
• Work with PostgreSQL and data-intensive applications.
• Use .NET Aspire for development and distributed application orchestration.
• Work with modern observability tools including OpenTelemetry and Grafana.
• Troubleshoot, debug and profile applications across backend and frontend layers.
• Contribute to CI/CD, Docker-based development and engineering best practices.
• Participate in the team's IT support rotation.
• Frontend: React / Next.js / TypeScript
• Observability: OpenTelemetry / Grafana

What we're looking for

You have 5+ years of full-stack development experience and are comfortable working across both frontend and backend technologies.

You bring

• Strong professional experience with C# / .NET.
• Strong experience with Python, ideally including FastAPI and Pandas.
• Solid knowledge of React, Next.js and TypeScript.
• Experience designing APIs and working with data-intensive applications.
• A good understanding of application performance and optimisation.
• Strong debugging and profiling capabilities.
• Experience working with modern software development practices.
• A pragmatic, root-cause-oriented approach to problem solving.
• The ability to work independently while collaborating closely with a small senior engineering team.

Nice to have

• Experience with OAuth2/OIDC or Keycloak.
• Experience with containerised environments and Docker.
• Knowledge of asynchronous or event-driven architectures.
• Experience with distributed systems and observability.
• Previous experience in EnergyTech, FinTech or another data-intensive industry.

What our client offers

• A key engineering position within a growing EnergyTech company.
• The opportunity to work on software directly supporting the European energy transition.
• A highly technical environment with a small team of experienced engineers.
• A flexible working model with regular face-to-face collaboration.
• Competitive fixed salary aligned with your experience.
• Performance-based variable compensation.
• Health insurance.
• Daily meal vouchers.
• Support with professional commuting expenses.
• Modern offices in Paris, 20th arrondissement.

Recruitment process

The process is designed to be fast and transparent:

1. Discovery Call - 30 minutes

An introductory conversation with the CEO to discuss your background, expectations and the company's vision.

2. Technical Interview - 60-90 minutes

A deeper technical discussion with the CTO and CSO, including a practical technical exercise relevant to the role.

3. Cultural Fit Lunch - approximately 60 minutes

An informal meeting with the founders to get to know each other and assess the overall fit.