Backend Engineer - Anti-Fraud
About Prelude
Prelude is redefining how companies onboard and authenticate users in a world where trust, speed, and conversion matter more than ever.
We help businesses verify users with less friction, higher security, and better economics, turning authentication from a cost center into a growth lever. Our flagship product enables companies to send OTP codes with the best price to conversion ratio on the market, dynamically selecting the most effective delivery channel in real time, from optimized SMS routing to messaging apps like WhatsApp. At the same time, Prelude actively blocks spam and fraud patterns that legacy providers routinely miss, protecting margins and user experience.
Founded in 2022 and backed by leading venture capital firms, Prelude has quickly reached strong product market fit and healthy financials, serving fast growing companies across Europe and expanding into the US market. Authentication is only the starting point.
With an ambitious roadmap and a pipeline of market defining products, we are building the platform for trust at scale, empowering companies to onboard users seamlessly, fight fraud intelligently, and grow globally with confidence.
About the team
Prelude was founded by former Zenly team members who experienced firsthand the limitations of existing authentication solutions. While building products used by millions, we saw how SMS authentication had become expensive, unreliable, and vulnerable to spam and fraud, ultimately leading to the creation of Prelude.
Today, we are a team of 40 and growing, based in Paris, building products that power secure and high-performance user onboarding for companies across Europe and the US. We believe small, highly skilled teams outperform large, fragmented organizations, and we are intentional about staying focused on impact, quality, and speed.
We operate with a flat organizational structure and value in-person collaboration, which helps ideas move faster, decisions stay grounded, and teams take full ownership of what they build.
Our values shape how we work every day:
Care
We care deeply about our customers, our teammates, and the quality and reliability of what we ship.Bias for Action
We move fast, test in the real world, and iterate quickly rather than over-optimizing in theory.Ownership
We take responsibility end to end, from identifying problems to delivering outcomes and learning from results.
These values underpin the company we are today and the team we are building for the future.
About the role
You'll start by working on Prelude's anti-fraud system. Here, you will analyse traffic patterns and work to help battle fraudulent attacks of all natures, for our customers.
You will take part in the continuous effort of making it better, faster and more reliable by working closely with engineers, a product designer and of course, customers.
As a new engineer within the Prelude Team, you have the opportunity to rapidly grow your skillset by working in a position that allows you to perform a wide array of tasks that extend from designing distributed systems, full-stack development and infrastructure management.
What you will do:
Building and scale a distributed system based on AWS technologies such as DynamoDB, SQS, Redshift and Lambdas and using the Go programming language.
Work on the next version of the Prelude anti-fraud system which we strive to be industry-leading in terms of usability, performance and functionality.
Ensure that our services are scalable, extensible, reliable, and performant.
Help deploy and scale our fraud prevention model to hundreds of large customers.
Develop and maintain internal tools to increase our efficiency.
Deploy and scale our fraud prevention model to hundreds of large customers.
Design and implement anti-fraud measures to detect and mitigate fraudulent authentication attempts.
Develop and execute complex SQL queries for data analysis, fraud detection, and customer insights.
Build statistical models and analytics dashboards to track user authentication trends and performance.
Deploy and fine-tune machine learning models to enhance fraud detection and authentication workflows.
Develop and maintain internal tools to increase efficiency and automate key processes.
Interact with customers daily to assist them and build features tailored to their needs.
About you:
You have experience working with large datasets, writing complex SQL queries, and analysing authentication patterns.
You have a strong technical background, including 4+ years of experience designing and engineering large-scale systems.
You have strong coding skills in Go
You prefer simple solutions and designs to complex ones, and have a good intuition of what will last a decade and scale.
You have a product-led mindset: you code for the output, not for the process.
You are fluent in english.
Nice to have:
Experience working with Rust, Typescript or any other highly scalable language is a plus
You have experience in anti-fraud engineering and can design systems to detect and prevent fraudulent activities.
What we offer:
Competitive compensation package with BSPCEs.
Hybrid working style: 3 days at the office and 2 day at home, with 4 weeks of remote per year.
We will provide you with the gear you need for your role (a laptop and a phone, for on-call rotations)
An annual offsite in a great location (last one was at La Pradet!)
Interview process :
The interview process will start with a 30 min introductory call followed by two technical assessments.
You will then be invited to our offices in Opera, where we will work together on a small practical project for about an hour, followed by a system design problem and an informal discussion about your past experiences and your working style.
We don't expect you to ace all these stages, we will evaluate your creativity and how you approach difficult problems. You should consider applying even if you don't meet all the criteria.