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sebastian.sigl
About

Hi. I'm Sebastian @sesigl Sigl.

Staff Engineer at Adevinta, working on search and relevance for Kleinanzeigen, Germany's largest marketplace. 18+ years building high-load systems, data products and platforms.

Sebastian Sigl speaking on stage
01

Short Bio

I am a software engineer with 18+ years of experience. I like problems where scale matters: search platforms, high-load server-side systems, and data- and machine-learning-driven products. I enjoy working close to the infrastructure, with containers and cloud-native technologies. Lately, a lot of my time goes into how AI changes the way we build software.

I write and speak about search, platform engineering, and AI-assisted development. This site collects what I build and what I learn along the way.

02

Career

At Adevinta, I work on search for Kleinanzeigen, Germany's largest marketplace. My focus is search relevance. I lead the migration from Elasticsearch to Vespa together with multiple teams, from relevance and architecture through to production.

I joined Core Ad Search in May 2026. Before that, I led multiple teams in advertising and built a greenfield retail media system for first-party ads. In both roles, I also work on making AI a practical part of how our engineers build software.

Kleinanzeigen is part of Adevinta, a group of classifieds marketplaces across Europe.

I believe anyone with a passion for technology can learn to code. That is why I create content: I write, give talks, and mentor engineers earlier in their careers. It also keeps me sharp and connected to the wider engineering community.

03

Experience

6 roles
  1. May 2026 – Present

    Staff Engineer (MTS 2) | Search Specialist, Core Ad Search

    Kleinanzeigen (Adevinta)

    I work on Kleinanzeigen Search, the search behind Germany's largest marketplace. My focus is search relevance. I lead the migration from Elasticsearch to Vespa, from relevance and architecture through to production. I also drive AI-assisted development: I build the tooling and run the training that help our engineers ship faster.

  2. Dec 2022 – May 2026

    Staff Engineer (MTS 2) | Architect, Advertising

    Adevinta

    I designed an in-house retail media platform for first-party ads and led multiple teams from domain design to production: feed ingestion of large advertiser catalogs, ad retrieval on Elasticsearch on Kubernetes, and integration with an external auction and budget-pacing service. I built the A/B testing setup for first-party ads and co-ran AI workshops for around 30 engineers, which later scaled to the whole Kleinanzeigen engineering organization.

  3. Oct 2018 – Dec 2022

    Classifieds Senior Full-Stack Engineer | Tech Lead Advertising

    eBay

    First as Senior Full-Stack Engineer, later as Tech Lead for advertising. I led the split of a Java monolith into microservices with domain-driven design and built the advertising configuration platform for first-party content and third-party ads. It delivered configuration at 50k requests per second, on Cassandra and Google Spanner with a React frontend, and contributed to 10%+ year-over-year ad revenue growth. I also grew the team with backend and frontend engineers.

  4. Oct 2016 – Sep 2018

    Senior Full-Stack Engineer

    MisterSpex

    I led the contact lens subscription project, which launched in Germany and Sweden in 2018 and brought recurring revenue. On the core shop platform, I helped move from a Java monolith to Spring Boot microservices on Docker and Kubernetes, and introduced React for the frontend.

  5. Oct 2014 – Sep 2016

    Full-Stack Software Engineer

    Sopra Steria

    I modernized a legacy Java Swing application and split frontend and backend out of a large monolith, and built web applications with Java, Spring, and ExtJS. I introduced a test-first approach that reduced post-deployment bugs by 30%, and helped the team adopt Scrum.

  6. Oct 2005 – Sep 2014

    High School, Computer Science Master & Freelancer

    Self-Employed

    I started coding as a teenager. At 17, I co-founded EliTurka, a social network for the Turkish market that was acquired before launch. After that, I did contract work for different companies while I finished high school and my Master's in Computer Science at Freie Universität Berlin.

04

Let's Connect

I am happy to talk about search, platforms, AI-assisted development, or new roles. Reach me by email or on X. I am not taking on freelance work right now, but I am always open to the right conversation.