> Markdown version of [/jobs/ext/3155763-senior-backend-developer](https://www.wearedevelopers.com/jobs/ext/3155763-senior-backend-developer). Every page supports `.md` or `Accept: text/markdown`. Links point to the HTML versions so they work for humans too. Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md). --- # Senior Backend Developer - **Company:** Lefebvre Sdu - **Location:** Den Haag, Netherlands - **Experience:** Expert - **Salary:** €5,500.0 - €6,450.0 - **Contract:** Permanent contract - **Skills:** Java (Programming Language), Artificial Intelligence, Software as a Service, Elasticsearch, Python (Programming Language), Operational Databases, Backend, Kotlin, Firepower - **Published:** September 9, 2026 - **Apply:** https://www.indeed.com/viewjob?jk=fdce31d0d4ba5063 ## About the Role You're an engineer who looks beyond the ticket. You want to understand why something is being built and what it delivers for the customer, and you're not afraid to have an opinion about it. You don't need a manager to make a technical call, and you speak up when you think something should be done differently. * Experience with Python and Java. Everything newly built is developed in Python, closely aligned with the AI teams who also work in it. But a large part of our current codebase runs on Java, so you need to be comfortable working with that too. * Experience with Elasticsearch. That's where it's determined which information the agent gets to see. * Experience with Scala or Kotlin is a plus. The ingestion layer runs largely on Scala. * You come from SaaS, a product-driven organization, or a scale-up, and you thrive on autonomy rather than oversight. ## Description Our Knowledge Team is the layer between the content and the AI. We pull in millions of documents from internal databases, public sources, and the web, standardize them, and make them usable for the AI agents that distill answers from them. The real challenge isn't storage but selection. Out of those millions of documents, exactly one paragraph needs to surface the moment a lawyer asks a question. Surface the wrong one, and the agent gives an answer that sounds plausible but is wrong. In our field, that's not a bug: it's a liability issue. What you build determines whether the answer holds up. There's work to be done, and it's the kind of work you could talk about for a whole evening. The pipeline has been running for six years, built in Scala and Java, and parts of it deserve a new foundation. Reranking is the biggest need: determining which passage, out of a mountain of legal documents, actually answers the question being asked. Not just which one contains the matching words. That's the problem we're solving. The team is strong on the scientific side, in retrieval, and in understanding what a model can and can't handle. What we're looking to add is engineering firepower: someone who can turn ideas into systems that deliver. Not to rebuild everything over six months just because it was once set up differently, but to see where the real gains are and start there. * You build and improve the pipeline that turns content into knowledge our AI agents can use. * You work on reranking quality, so the agent gets the right information, not just the most information. * You help shape the approach to retrieval and knowledge extraction, bringing in what you've seen work elsewhere. * You work in Python for everything new, and in Java where the existing codebase calls for it. * You make technical decisions, even when no one is looking over your shoulder. ## Related Videos - [Inside Bitpanda's Tech Stack: Scaling a European Fintech Leader - Markus Dorner](https://www.wearedevelopers.com/videos/1979-inside-bitpanda-s-tech-stack-scaling-a-european-fintech-leader-markus-dorner) - [Developing the Backend with Stefan Lingler, CTO at Shpock](https://www.wearedevelopers.com/videos/100360-developing-the-backend-with-stefan-lingler-cto-at-shpock) - [Kotlin Multiplatform - True power of native code reuse](https://www.wearedevelopers.com/videos/4-kotlin-multiplatform-true-power-of-native-code-reuse) - [Next Level Enterprise Architecture: Modular, Flexible, Scalable, Multichannel and AI-Ready?](https://www.wearedevelopers.com/videos/1017-next-level-enterprise-architecture-modular-flexible-scalable-multichannel-and-ai-ready) - [Nest.js - TypeScript in the backend can also be clean](https://www.wearedevelopers.com/videos/1033-nest-js-typescript-in-the-backend-can-also-be-clean) - [Why Kotlin is the better Java and how you can start using it](https://www.wearedevelopers.com/videos/661-why-kotlin-is-the-better-java-and-how-you-can-start-using-it) ## Related Articles - [Fully Remote Software Engineer Jobs](https://www.wearedevelopers.com/magazine/447-fully-remote-software-engineer-jobs) - [Is Software Engineering Over-Saturated?](https://www.wearedevelopers.com/magazine/418-is-software-engineering-over-saturated) - [Highest Paying Tech Companies for Developers](https://www.wearedevelopers.com/magazine/220-highest-paying-tech-companies-for-developers) - [The 7 Most Popular Backend Frameworks for Developers](https://www.wearedevelopers.com/magazine/403-the-7-most-popular-backend-frameworks-for-developers) - [Why Upskilling And Reskilling is Important For Developers](https://www.wearedevelopers.com/magazine/428-why-upskilling-and-reskilling-is-important-for-developers) - [What’s the Difference Between Frontend and Backend Development?](https://www.wearedevelopers.com/magazine/240-what-s-the-difference-between-frontend-and-backend-development)