I gave a coding agent the same job four different ways and measured what each cost. The packaging barely mattered, but something else did.At OLX, we’ve been pushing to get AI tools into everyday engineering work. This has enabled us to have faster delivery and better test coverage, with less time spent on the mechanical parts. Our biggest constraint, however, is tokens. Tokens being a finite resource, we keep running up against our allocated quota. So the real question is how to get the best results per token spent.There’s no shortage of advice on how to feed context into agents: put…
IntroductionAt OLX, professional sellers pay for higher-tier packages because they promise more exposure. More visibility, and, in theory, better results. But when we looked at the data, something unexpected happened. In some cases, ads published with premium packages appeared to perform worse than ads using cheaper packages.That raised an uncomfortable question: If higher-tier packages provide more exposure, shouldn’t they consistently perform better?At first glance, there were several possible explanations. Perhaps the extra visibility weren’t creating as much value as we expected. Perhaps…
Image by the_iop from PixabayConcurrency in programming is the ability to manage and execute multiple tasks or processes at the same time (or appear to), allowing programs to remain responsive and efficient. Think of it like a chef in a busy kitchen: they’re not cooking every dish from start to finish sequentially, but instead chopping vegetables while one pan simmers and another bakes; juggling progress on several tasks concurrently.I’m a frontend engineer at OLX working mostly with React and NextJs, but I also came from a background in which I worked primarily in concurrent programs with…
Our Work Organization Framework JourneyPhoto by Daniel Watson @pexelsWhat Makes Cross-functional Collaboration Actually Work?In today’s cross-functional environments, the most impactful initiatives rarely live within the boundaries of a single team or person. Whether we’re building new product features, improving infrastructure, or tackling technical debt, success depends on seamless collaboration across multiple teams and roles, including engineering, product, design, analytics, and beyond.Think about when you’re making a big dinner for friends. You might be the main cook, but you need…
The always-evolving challenges of OLX create a rich environment for innovation, experimentation, and knowledge sharing. In our 2026 Frontend Masterclass, we have three sessions that will shed light on our current development flow.Join us on March 3rd, 2026, from 6:00 pm to 9:00 pm at our OLX Offices in Poznań!Do you want to join us and know what’s trending in the latest frontend technology? Check the event information and join here!Can’t join it in person? Sign in to this form to receive the online recording of the session!Our AgendaWith a broad schedule, our speakers will deliver a mix of…
The Importance of Offline Evaluation to Guide Model ChoiceIntroductionRecent advancements in open-source AI models make it challenging to justify the development of custom models, given the high quality of existing options. This also applies to embedding models, which are available in impressive quality.At OLX, we utilize a model called Item2vec to generate similar item recommendations. For more details, please refer to our blog post.Item2Vec: Neural Item Embeddings to enhance recommendationsIn this work, we developed an embedding model that not only improved recommendations but was also used…
Hybrid Search — Where Keywords Meet Vectors, Enabling Classifieds DiscoveryIn the midst of a fast-paced technological revolution, where user expectations grow increasingly sophisticated, the quality of search in the classifieds space has never been more critical. In fact, users expect the search box to understand what they are looking for and produce relevant search results; if this is not the case, they will easily move on to any competitor who provides this experience.At OLX, our search system traditionally relied on keyword matching between user queries and ad titles and descriptions — a…
generated by chatgptIntroductionIn the world of A/B testing and experimentation, it’s tempting to check results frequently and stop tests earlier if they seem significant (a practice known as peeking). However, this practice dramatically inflates the false positive rate, leading to misleading conclusions.Imagine you’re running an A/B test, and after just 10 days, the results look like a clear win. You might be tempted to end the experiment early and move forward with the release of the new feature. After all, why wait another two weeks as originally planned? But here’s the catch: the more…
Optimizing FastAPI at Scale: Lessons from OLX’s Recommendation PlatformPhoto by Rosy KoIn distributed systems, there is a motto that says ‘you are as slow as your slowest tasks’. In Python, thanks to the notorious Global Interpreter Lock (GIL), this issue is amplified: ‘your slowest task will make every other task slower’. In this article, I’ll walk you through the optimizations we made to scale a FastAPI service that now handles tens of thousands of requests per second, achieving a p99 latency under 10ms.IntroductionOLX is a global online marketplace that enables users to buy and sell goods…
As software systems continue to grow in complexity, the demand for effective configuration management tools becomes not just important but essential. Our work on Learning to Rank (LTR) projects exemplifies this challenge.At OLX we use LTR to improve the search results based on their relevance. This involves training models to rank ads based on various features, ensuring that the most relevant ones appear at the top of the list. The resulting sorting can be found under the ‘Recommended Ads’ option, the default option currently live on our OLX websites in several countries.Given the potential…
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