Yonatan Karp-Rudin

Portfolio, writing, and engineering

Yonatan Karp-Rudin builds backend systems that survive contact with reality.

Based in Berlin. Staff engineer at Billie, working across backend architecture, distributed systems, platform engineering, and the operational detail that decides whether a system feels trustworthy in production.

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Current focus Distributed backend systems, API-first architecture, and production-grade platform work
Writes about Kotlin, debugging, observability, backend design tradeoffs
Open source ff4k, openapi-generator, Konsist, practical library work
Portrait of Yonatan Karp-Rudin

Start here

XKCD: From Tile to Picture - Seeing the Full Image

A step-by-step walkthrough of reconstructing the massive XKCD #1110 Click and Drag comic from its individual tile images using Kotlin.

Yonatan Karp-Rudin

About

Twelve years across infrastructure, payments, internal platforms, and engineering writing.

Today Yonatan works at Billie on backend systems and service architecture, building the kind of platform and operational foundations that make complex products easier to evolve. Before that he built backend platforms at SumUp, vision-processing systems at Inuitive, and the kind of internal tools that quietly make engineering teams faster and calmer.

The thread through all of it is not a single stack, but a way of operating: API-first thinking, careful decomposition, clear technical writing, and improving systems without turning them into theater.

Works across Kotlin, Java, Spring Boot, Flink, Kafka, and service architecture at scale
Bias toward Clear contracts, production trust, and practical engineering judgment

Experience

Roles where architecture, product, and execution meet

Oct 2025 - Present

Staff Software Engineer

Billie, Berlin, Germany

Staff Software Engineer - Payments

Established the Compliance Service as a new domain covering transaction monitoring, screening, and sanction checks – authored the tech spec, interface definitions, and led the ComplyAdvantage integration. Built a cronjob monitoring tool in Backstage aggregating data across multiple systems. Authored operational runbooks for Kafka DLT alerts, settlement reports, and compliance state handling. Member of the architecture team. Drove Spring Boot 3 to 4 migration including upstream contributions to openapi-generator for Jackson 3 support.

Apr 2025 - Oct 2025

Staff Software Engineer

Billie, Berlin, Germany

Staff Software Engineer - Risk

Co-designed and built the Risk Orchestrator service using hexagonal architecture. Led the Ravelin integration for improved fraud detection, including release planning and cross-team coordination. Authored the Buyer Risk Assessment target architecture. Wrote specs for tokenization, direct debit risk, and recurrent identification. Drove API-first with OpenAPI across all risk services. Led “EDA 2.0” to improve event-driven architecture practices.

Nov 2023 - Apr 2025

Senior Software Engineer

Billie, Berlin, Germany

Senior Software Engineer - Risk

Built real-time fraud detection features with Apache Flink (velocity features per email/device). Led the graph database POC (Neo4j) for fraud detection, later extended with IBAN integration. Enabled the risk scoring model and introduced provider fraud labelling for refinancing. Applied engineering best practices to Python CI/CD pipelines. Managed Kafka infrastructure via Terraform (topic creation, permissions, DLT retention). Attended Flink Forward 2024 and brought learnings back to the team.

Jun 2019 - Nov 2023

Backend Software Developer

SumUp, Berlin, Germany

Backend Software Developer

Built a unified money library used across backend and Android. Created an authorization and permissions management library. Designed a sales management platform with clean domain separation. Migrated 6 years of historical data with minimal production impact using a separate deployment strategy. Reduced new service setup from 1 week to 1-2 hours with a repository template. Implemented service-level objective monitoring. On-call for critical payment systems.

Dec 2017 - May 2019

Backend Software Developer

NICE, Ra'anana, Israel

Backend Software Developer

Java and Python application development on distributed systems. Refactored a product’s cache system improving performance and reliability. Built an automated release notes generator integrating Python 3 and Jira.

Aug 2014 - Dec 2017

C++/C# Junior Developer

Inuitive, Ra'anana, Israel

C++/C# Junior Developer

Developed algorithms on next-generation vision processing chips in C++. Created calibration processes for production lines (C++, C#, Python, Matlab). Established production lines in South Korea and China – logistics, equipment setup, and training.

Education

Courses, degrees, and topics that keep showing up in the work

2024

Workshop

Advanced Software Architecture with Residuality Theory

Advanced Software Architecture Workshop with Residuality Theory

View credential

2023

Udemy

Software Architecture & Design of Modern Large Scale Systems

Software Architecture & Design

View credential

2012-2016

B.Sc. Computer Science

Reichman University

Projects and contributions

Libraries, experiments, and products that were built to solve real problems.

01

ff4j (contributor)

Authored the javax-to-jakarta namespace migration. Merged but never released by maintainers – the motivation for building ff4k.

2026

GitHub
02

TaleKeeper

AI-powered TTRPG session recorder with live transcription, speaker diarization, and session summaries. Python/FastAPI backend + Svelte 5 frontend. Fully self-hosted.

2026

Docs
03

sse-mcp-server

Kotlin-based SSE MCP server for tool execution in AI agents (Flowise).

2026

GitHub
04

ff4k

Kotlin Multiplatform feature flags library with DSL configuration, multiple storage backends (JDBC, R2DBC, SQLite), and coroutine-safe context propagation. Built from scratch as a modern alternative to ff4j.

2025

Docs
05

poor-life-choices

Mead sharing app for friends. JavaScript/React, live on Vercel.

2024

Visit
06

Konsist (contributor)

CI pipeline improvements, snippet verification, and null handling fixes for the Kotlin static code analyzer. 3 merged PRs.

2023

GitHub

Writing

Notes from debugging, design tradeoffs, and the parts of backend work worth explaining properly.

Recommendations

Things people actually said after working together

Yonatan Karp-Rudin
Blake Irvin Leading Observability Engineering at SumUp
I’d love to work with Yonatan again. He’s incredibly smart, cares deeply about quality but balances this with delivery speed, and (maybe most importantly) a great human to be teammates with.
Yonatan Karp-Rudin
Oren Hadry Former Engineering Manager at Inuitive
I was privileged to have Yonatan on my team for almost 3 years. Yonatan is a dedicated, intelligent, and hard-working team player who played a key role in our team and was the go-to person for almost any problem. I have seen few people who could match his skills at solving technical problems, coding and design.
Yonatan Karp-Rudin
Shimon Schocken Computer Science Professor, Reichman University
Yonatan is a highly talented and disciplined software developer, with an excellent background in both computer science and programming. He is a people-person, with remarkable empathy and ability to recognize when and where students and developers need help and further guidelines. He is also a very pleasant and good-spirited colleague.

Contact

If there is something worth building together, let's talk

Roles, consulting, architecture reviews, collaboration, or just a good conversation about backend systems.

Based in Berlin, Germany
Best for Staff-level backend roles, platform work, and distributed systems
GitHub github.com/yonatankarp LinkedIn linkedin.com/in/yonatankarp