Freelance Staff Backend Engineer (Ruby) M/F/Mx

Trustpair; Paris; Hybrid; EUR 110,000 - 207,000; Full time

Job summary

Trustpair is seeking a Senior Freelance Staff Software Engineer to join our Core Evaluation squad in Paris (hybrid) or fully remote from France. You will be the technical authority shaping our fraud‑detection engine, architecting scalable, resilient solutions and guiding the integration of LLM‑based insights.

You’ll collaborate with Engineering Manager, Product Manager and engineers to translate strategic vision into technical reality, driving complex initiatives from concept to execution in a

Qualifications

• 8 years experience with high‑throughput environments.
• 2–3 years with Ruby on Rails.
• Proven architect of large‑scale systems, with asynchronous workflows.
• Observability expertise with Datadog, Prometheus, Grafana.
• DevOps mindset and experience scaling apps on Kubernetes.
• Performance optimization across applications, databases and infra.
• Strong collaboration in agile teams and influence without authority.
• Continuous learner keeping up with evolving tech.

Responsibilities

• Architect and Own: design the technical vision for large‑scale, distributed systems central to our platform.
• Lead Technical Strategy: drive complex projects from conception to completion.
• Shape the Future: partner with leadership to refine the technical roadmap and tackle challenges.
• Drive Innovation: apply LLM‑based solutions to improve the Trustpair engine.
• Mentor and Elevate: act as a technical mentor across squads.
• Ensure Operational Excellence: promote observability, scalability and performance.

Skills

Leadership

Collaboration

Problem solving

Customer focus

Tools

Ruby on Rails

Datadog

Prometheus

Grafana

Kubernetes

PostgreSQL

Job description

About

Trustpair stops vendor fraud before it happens. We're the automated vendor validation platform protecting 400+ enterprise companies worldwide. Since 2017, finance and procurement teams have used Trustpair to eliminate vendor fraud while reclaiming 90% of the time they once spent on manual checks. As vendor fraud grows more sophisticated, we stay ahead by combining deep expertise in financial crime with cutting-edge technology. Our core product focuses on secure, reliable vendor account validation to wipe out fraud and boost efficiency. Internally, teams across Trustpair use AI tools in their day‑to‑day work to automate repetitive tasks and unlock strategic insights that help us build and operate better. From day one, you’ll be encouraged and trained to integrate these tools into your workflow in a practical, hands‑on way. With offices in New York, Paris, London, and Milan, we're a diverse team united by a bias for action. We ship fast, learn from experiments, and tackle problems that matter: protecting billions in payments for companies worldwide. If you want to see your work make an immediate impact in financial security, Trustpair is built for you. Learn more about how we use AI in everyday work here.

Job Description

Trustpair stops vendor fraud before it happens. We're the automated vendor validation platform protecting 550+ enterprise companies worldwide. Since 2017, finance and procurement teams have used Trustpair to eliminate vendor fraud while reclaiming 90% of the time they once spent on manual checks. As vendor fraud grows more sophisticated, we stay ahead by combining deep expertise in financial crime with cutting-edge technology. Our core product focuses on secure, reliable vendor account validation to wipe out fraud and boost efficiency. Internally, teams across Trustpair use AI tools in their day‑to‑day work to automate repetitive tasks and unlock strategic insights that help us build and operate better. From day one, you’ll be encouraged and trained to integrate these tools into your workflow in a practical, hands‑on way. With offices in New York, Paris, London, and Milan, we're a diverse team united by a bias for action. We ship fast, learn from experiments, and tackle problems that matter: protecting billions in payments for companies worldwide. If you want to see your work make an immediate impact in financial security, Trustpair is built for you. Learn more about how we use AI in everyday work here.

About The Role

As a Freelance Staff Software Engineer on our Core Evaluation team, you will be a technical authority driving the evolution of our most critical asset: the fraud detection engine. This is a pivotal role where you'll architect for scale and resilience, while helping us rethink our evaluation process through the integration of LLM‑based insights.

We will bring you in to lead some of our most complex and ambitious technical initiatives, shaping advanced solutions from ambiguous requirements through to execution. Working within a dedicated squad, you will collaborate closely with our Engineering Manager, Product Manager, and engineers to turn strategic vision into technical reality and further strengthen Trustpair’s position as a market leader.

Contract type: Freelance / Contractor

Location: Paris (hybrid) or full remote from France

What You’ll Do

We’re looking for a senior freelance engineer who can quickly create impact in a scale‑up environment and operate with a high degree of autonomy.

• Architect and Own: Design, architect, and own the technical vision for large‑scale, distributed systems at the heart of our platform, with a focus on our complex evaluation workflows.
• Lead Technical Strategy: Lead complex, cross‑functional technical projects from conception to completion, ensuring alignment with product strategy and client needs.
• Shape the Future: Partner with Product and Engineering leadership to build and refine the technical roadmap. You will identify key technical challenges and propose innovative solutions that drive our business forward.
• Drive Innovation: Champion a culture of innovation and continuous improvement. You will be directly involved in transforming the Trustpair engine by exploring and implementing new technologies, with a strong focus on applying LLM‑based solutions to solve complex business problems.
• Mentor and Elevate: Act as a technical mentor and force multiplier for engineers within your squad and across the organization, promoting best practices in software architecture, design, and strategic thinking. Help the engineering manager drive the cultural shift to strengthen the customer focus.
• Ensure Operational Excellence: Promote and implement best practices for observability, scalability, and performance, ensuring our core systems are reliable and efficient.

What’s in it for you?

• High‑Impact Freelance Mission: Join a company with 50%+ business growth where tech is one of the core accelerators. You’ll be building solutions for a platform with rapidly increasing usage, directly influencing our success.
• Shape Our Future (Scaleup Phase): We want your voice in making the critical architectural, product, and organizational decisions that will define our future.
• Modern Stack & AI-Powered Engineering: Work with a clean Ruby on Rails stack, state‑of‑the‑art DevOps, and managed tech debt. We are aggressively adopting AI, both in our product (LLMs) and to boost your own efficiency with tools like Claude Code and Cursor.
• Strong Ownership: You are an engineer with a strong voice and full accountability. We empower you to drive initiatives from technical design to final impact.
• Accelerated Career Growth: Our rapid expansion creates constant and significant opportunities for career advancement, skill development, and taking on new leadership responsibilities.
• Collaborative & International Team: Thrive in a diverse, cross‑functional, and international environment.

Why join Trustpair? A list of our perks here!

Must Haves

• Mission‑Driven & Customer‑Focused: You are passionate about solving real‑world problems and are driven to connect technical solutions with customer value and business impact.
• Deep Technical Expertise: You have 8 years experience with technologies in high‑throughput environments, with at least 2‑3 years in Ruby on Rails.
• Proven Architect: You have a proven track record of architecting, building, and operating complex, large‑scale systems, particularly those with asynchronous workflows and demanding workloads.
• Observability Expert: You have hands‑on experience implementing and leveraging observability tools (e.g., Datadog, Prometheus, Grafana) to ensure system health and performance.
• DevOps & Infrastructure Acumen: You possess a strong DevOps mindset and practical experience in scaling and tuning applications on container orchestration platforms like Kubernetes.
• Performance Master: You have deep expertise in performance analysis and optimization, capable of debugging bottlenecks in application code, databases (e.g., PostgreSQL), and infrastructure.
• Collaborative Leader: You have excellent communication and collaboration skills, with a history of working effectively in agile teams, partnering with product management, and influencing technical direction without direct authority.
• Continuous Learner: You maintain a strong technical watch on the evolving ecosystem, knowing how to identify and apply best practices from different communities to solve problems creatively.

Bonus Points

• Direct experience in designing, building, and deploying applications powered by Large Language Models (LLMs).
• Experience working in a high‑growth B2B SaaS environment.
• A data‑driven approach to decision‑making, from product analytics to application monitoring.

Recruitment Process

• First call with Talent Acquisition (30 mins)
• Experience interview with Benoit, CTO (1h)
• Case study onsite with our Engineering team
• Coffee fit with two members of our Engineering & Product teams (30 mins)
• Cofounders interview with Alex, Cofounder & MD (45 mins)

Equal Opportunity Statement

Trustpair's policy is to provide equal employment opportunity in all of our employment practices without regard to race, color, religion, sex, national origin, ancestry, marital status, protected veteran status, age, individuals with disabilities, sexual orientation or gender identity or expression or any other legally protected category.

Applicants for all positions in Trustpair must be legally authorized to work in the country which they are applying for or be a citizen from Schengen / EU zone. The verification of employment eligibility will be required as a condition of hire.

Additional Information

• Contract Type: Freelance
• Location: Paris