Senior Full Stack Engineer

WelcomeTrack; Paris; Hybrid; EUR 90,000 - 130,000; Full time

Benefits offered by this job

Hybrid work schedule

Health insurance (mutuelle)

Meal vouchers

Public transport subsidy

Job summary

WelcomeTrack is seeking a Senior Full Stack Engineer to design, develop, and maintain scalable server and client components. You will collaborate with a cross-functional squad to deliver features, improve system architecture, and ensure high-quality deliverables that meet technical and business goals.

You will work with Engineering Managers, Product Managers, and other engineers in an agile environment. The role emphasizes code quality, performance, security, and strong testing practices within

Qualifications

• 5+ years of professional software development with back-end and front-end experience.
• Proven experience designing scalable architectures, RESTful APIs and data models.
• Strong knowledge of relational databases and performance optimization.
• A strong testing culture with unit/integration tests (TDD preferred).
• Experience running production systems with monitoring and incident management.
• Ability to mentor engineers through code reviews and pairing.
• Professional English for international collaboration.

Responsibilities

• Design, develop, and maintain scalable back-end services and front-end apps.
• Build and optimize database schemas and data models.
• Write clean, tested code following team standards.
• Participate in code reviews and provide feedback.
• Debug production issues and implement robust solutions.
• Contribute to architecture decisions and technical docs.
• Design and implement RESTful APIs.
• Optimize performance and scalability; implement caching and async processing.
• Engage in agile ceremonies and planning.
• Collaborate with PMs, Designers and Engineers to prioritize work.
• Handle support requests and bug fixes within SLAs.

Skills

RESTful APIs

Data modeling

Relational databases

Testing culture

Production systems

Code reviews

English communication

Tools

Docker

Kubernetes

AWS

Datadog

Sentry

Elixir/Phoenix

Job description

As a Full Stack Engineer you are responsible for designing, developing, and maintaining both the server-side and client-side components of our software applications. This role requires expertise in full-stack technologies and the ability to build robust, scalable systems while collaborating effectively within an agile team environment. This position involves working closely with Engineering Managers, Product Managers, and other team members to implement features, improve system architecture, and ensure high-quality deliverables that meet both technical and business requirements. The Full Stack Engineer will be part of a cross-functional squad and will contribute to technical decisions while maintaining high standards of code quality, performance, and security.

Technical development

• Design, develop, and maintain scalable back-end services and APIs as well as front-end applications

• Build and optimize database schemas and data models

• Write clean, maintainable, and well-tested code following team standards and best practices

• Participate in code reviews and provide constructive feedback to team members

• Debug production issues and implement robust solutions

• Contribute to technical documentation and architecture decisions

• Design and implement RESTful APIs

• Optimize application performance, database queries, and system scalability

• Implement caching strategies and asynchronous processing systems

• Participate in agile ceremonies and technical planning sessions

Collaboration and innovation

• Actively participate within an autonomous mission team (PM, Designer, Engineering Manager, other Engineers) to clarify priorities and user needs

• Contribute to technical discussions and architecture decisions

• Collaborate with team members to define API contracts and data structures

• Participate in squad rituals and team meetings

• Handle support requests and bug fixes within agreed SLAs

Quality & best practices

• Write unit tests and integration tests following TDD principles

• Collaborate with QA team to ensure comprehensive test coverage

• Participate in pair programming sessions with team members

• Monitor application performance, scalability, and implement improvements

• Follow security best practices and address vulnerabilities proactively

• Contribute to continuous integration and deployment processes

• Implement logging, monitoring, and alerting systems

• Ensure data integrity and implement backup strateg

• Hybrid work: 2 days on site in Paris, 2 days remote, as part of our 4-day week
• Health insurance (mutuelle)
• Meal vouchers
• 75% of your Navigo pass covered

Must-have

• 5+ years of professional software development, with significant experience on both back-end and front-end
• Proven experience designing scalable architectures, RESTful APIs and data models
• Strong knowledge of relational databases and performance optimization (queries, caching, asynchronous processing)
• A strong testing culture (unit, integration, TDD), and you're the one who raises the bar on code quality
• Experience running production systems: monitoring, alerting, incident management
• Ability to mentor other engineers through code reviews, pairing and knowledge sharing
• Professional English, as you'll work with international teammates

Nice-to-have

• Experience with our stack (Elixir / Phoenix, React / TypeScript, PostgreSQL), or the motivation to learn it quickly
• Experience with high-traffic products
• Familiarity with Datadog, Sentry, Docker, Kubernetes or AWS
• Experience in a product company or a SaaS environment