Senior Backend Engineer

Leonar; Paris; On-site; EUR 70,000 - 110,000; Full time

Job summary

Leonar, based in Paris or Bordeaux, is seeking a Senior Backend Developer to join its Tech team. You will work with the Head of Software on scaling systems, architecture, and high-impact feature development.

Expect to own backend topics, improve performance, and contribute to a production-first environment with frequent releases and real-time data handling.

Qualifications

• 5+ years in software development.
• Strong Python background.
• Experience in R&D or product-driven tech teams.
• Excellent communication, written and verbal.

Responsibilities

• Feature development: build new product features and contribute to the technical roadmap.
• Infrastructure maintenance & improvement: maintain systems, troubleshoot incidents, improve backend services.
• Performance optimisation: improve capacity planning and scalability.
• Complex problem-solving: own deep technical challenges to ensure robustness of the platform.

Skills

Python

Node.js

Go

Software development

Problem solving

Job description

About The Role

Based in Paris or Bordeaux, the future Senior Backend Developer will be a key player in our Tech team. Working closely with our Head of Software, you’ll help us scale our systems and accelerate our product development. This role is a mix of deep technical ownership, hands‑on architecture work, and high‑impact feature development.

About The Role

Based in Paris or Bordeaux, the future Senior Backend Developer will be a key player in our Tech team. Working closely with our Head of Software, you’ll help us scale our systems and accelerate our product development. This role is a mix of deep technical ownership, hands‑on architecture work, and high‑impact feature development.

Inside our Tech team, you’ll find five developers working with high agility. We deploy to production daily and release new app builds every week. We manage a wide range of applications (six in total), all built on very solid foundations. Our system handles tens of thousands of trips per day and hundreds of real‑time messages per second between our servers and our connected vehicle fleet.

Every developer works on high‑impact projects, tackling exciting technical challenges: improving performance, optimising request loads, and laying the groundwork for tomorrow’s more complex features. We’re building for scale, preparing to absorb 10 times more users and trips in the coming months, so we are looking for someone who is curious, sharp, and deeply technical with the desire to take ownership and work across a wide range of backend topics.

Key Responsibilities

• Feature development: Build new product features and contribute to the technical roadmap, designing solutions that balance user needs with strong technical foundations.
• Infrastructure maintenance & improvement: Maintain existing systems, troubleshoot incidents, and continuously improve backend services.
• Performance optimisation: Reduce recurring incidents, improve capacity planning, and optimise backend architecture to ensure scalability and reliability.
• Complex problem‑solving: Take ownership of deep technical challenges to ensure the robustness and quality of our platform.

Profile

• Experience: 5+ years in software development, ideally in R&D environments or within product‑driven tech teams.
• Tech stack: Strong background in Python; familiarity with Node.js or Go is a plus.
• Problem‑solving mindset: You approach problems with pragmatism, balancing quick wins with long‑term solutions that scale.
• Ownership & impact: You care about building the right thing, and building it right. You take full responsibility for your work and its impact on users and the product.
• Communication: You express complex ideas clearly, both in writing and verbally, and adapt your messaging to your audience, whether technical or not.
• High standards: Obsessed with clarity in code, in architecture, and in how things fit together, you bring strong opinions backed by experience.
• Bonus (optional): Real‑time systems — a first experience with high‑frequency, low‑latency systems and ensuring smooth communication between distributed components / IoT devices.

Hiring Process

• Pre‑screening with Head of Software: 15‑minute intro video call
• Initial call with HR: 30‑minute conversation to align on expectations
• Culture fit test: Short written exercise (10 minutes)
• Case study & Manager interview: Hands‑on exercise to assess your technical skills, followed by a discussion with the Head of Software
• Founders meeting: Final conversation with the founders to dive into vision, motivations, and team fit