Senior Backend Developer

team.blue

Senior Backend Developer at Kolsquare responsible for backend system design and optimization. Contribute to feature delivery using Ruby on Rails for Europe's leading influencer marketing platform.

Posted 6/1/2026full-timeRemote • 🇫🇷 FranceSeniorWebsite

Tech Stack

Tools & technologies

CloudDistributed SystemsElasticSearchGoogle Cloud PlatformMySQLRubyRuby on Rails

About the role

Key responsibilities & impact

Design, develop, and maintain backend services and APIs using Ruby on Rails.
Implement new features for the SaaS platform, write clean and maintainable code, and ensure the scalability and performance of the application.
Contribute to backend architecture decisions, improve system scalability, and optimize database queries and search performance using Elasticsearch.
Collaborate with product, frontend, and DevOps teams to deliver high-quality features.
Participate in code reviews, maintain testing standards, contribute to CI/CD processes, and support best engineering practices within the team.

Requirements

What you’ll need

Strong experience with Ruby on Rails in production environments
Solid experience designing and maintaining RESTful APIs
Hands-on experience with Elasticsearch or search systems
Strong knowledge of relational databases (MySQL preferred) and query optimization
You want to join an adventure more than a job! Kolsquare is a benefit company, with a general interest ambition that goes beyond our profitability goals: positively impact the world.
Nice-to-haves:
Experience working on SaaS platforms or high-scale applications
Familiarity with cloud environments (GCP) and CI/CD pipelines
Experience with performance optimization, background jobs, and distributed systems.

Benefits

Comp & perks

Full flexibility: full remote work with European hubs and 400+ coworking spaces worldwide.
Monthly and quarterly highlights in person to get together with other Kolsquarians for great team building events.
A package linked to the market that will not be based on your location.
The stability and resources of a profitable group, with the agility of a scale-up.
Continuous training opportunities and career development support.

ATS Keywords

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Applicant Tracking System Keywords

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Hard Skills & Tools

Ruby on RailsRESTful APIsElasticsearchMySQLquery optimizationperformance optimizationbackground jobsdistributed systemsSaaS platformsCI/CD