How to Fix Misconfigurations in RedisTemplate· Jun 2024A practical guide to identifying and fixing common RedisTemplate misconfiguration pitfalls in Spring Boot, with a focus on serialization issues.
How To Build Your Domain Gateway With OpenAPI· Dec 2022An introduction to the domain gateway pattern and a practical tutorial for building one in Kotlin using OpenAPI code generation.
How to Use OpenAPI to Build a Robust RESTful API· Dec 2022How to adopt a spec-first approach with OpenAPI to design and generate a robust, well-typed REST API using Spring Boot, Kotlin, and Gradle.
Case study · Compliance platformCreating a new service boundary for compliance workflows.
Case study · Engineering leverageTurning repeated operational friction into shared tooling.
Owns payments/compliance platform reliability across service boundaries, vendor integrations, migration work, and operational tooling.
Took ComplyAdvantage transaction monitoring live, validated in shadow mode before blocking payments.
Rebuilt the compliance service around hexagonal architecture and a transactional outbox.
Designed the dead-letter and replay pattern for payment services and shipped it as a shared Spring Boot library.
7
Billie, Berlin, GermanyOct 2025 – Present
Staff Software Engineer, Payments
Owns payments/compliance platform reliability across service boundaries, vendor integrations, migration work, and operational tooling.
What I did
Took ComplyAdvantage transaction monitoring live, validated in shadow mode before blocking payments.
Rebuilt the compliance service around hexagonal architecture and a transactional outbox.
Designed the dead-letter and replay pattern for payment services and shipped it as a shared Spring Boot library.
Built a Backstage Payments Hub that replaced Postman workflows, and on-call triage tooling used across about 80 production incidents.
Case study
Compliance platform
Creating a new service boundary for compliance workflows.
Context
Transaction monitoring, screening, and sanction checks crossed product rules, vendor behavior, alerts, and audit expectations.
Decision
I authored the technical spec and interfaces, led the ComplyAdvantage integration, and covered Kafka DLT alerts, settlement reports, and compliance states in the service design.
Result
Scattered operational knowledge became a service teams can reason about, monitor, and recover.
Case study
Engineering leverage
Turning repeated operational friction into shared tooling.
Context
Platform work gets expensive when incidents, cronjobs, migrations, and service setup depend on private memory.
Decision
I build Backstage tools, templates, migration plans, and upstream fixes when the reusable path beats another one-off patch.
Result
Engineers start from a known path and can challenge decisions through specs, dashboards, examples, and code.
6Billie, BerlinApr 2025 – Oct 2025
Staff Software Engineer, Risk
Case study · Risk architectureMoving risk work toward explicit orchestration and contracts.
Led Staff-level risk work: moving risk decisions into a Risk-owned orchestrator, the Ravelin fraud integration, and the target architecture for buyer risk.
Moved risk decisions from Purchases to a Risk-owned orchestrator, from RFC to production.
Led the Ravelin graph fraud integration to production.
Authored the Buyer Risk Assessment target architecture and the tokenization specification.
6
Billie, Berlin, GermanyApr 2025 – Oct 2025
Staff Software Engineer, Risk
Led Staff-level risk work: moving risk decisions into a Risk-owned orchestrator, the Ravelin fraud integration, and the target architecture for buyer risk.
What I did
Moved risk decisions from Purchases to a Risk-owned orchestrator, from RFC to production.
Led the Ravelin graph fraud integration to production.
Authored the Buyer Risk Assessment target architecture and the tokenization specification.
Case study
Risk architecture
Moving risk work toward explicit orchestration and contracts.
Context
Risk decisions depended on multiple services, fraud providers, recurrent identification, tokenization, and direct debit behavior.
Decision
I co-designed the Risk Orchestrator, pushed OpenAPI-first contracts across risk services, led the Ravelin integration, and authored the Buyer Risk Assessment target architecture.
Result
Risk changes gained a clearer coordination model across providers, payment behavior, and service boundaries.
5Billie, BerlinNov 2023 – Apr 2025
Senior Software Engineer, Risk
Built Risk's credit limit and fraud-labelling services, and moved risk signals to event-driven, engineering-owned pipelines.
Built a credit limit service and a fraud-labelling service from scratch.
Replaced synchronous calls between Risk and Refinancing with an event-driven credit score for Pan-European refinancing.
Moved real-time fraud features from Data Science to Engineering.
5
Billie, Berlin, GermanyNov 2023 – Apr 2025
Senior Software Engineer, Risk
Built Risk's credit limit and fraud-labelling services, and moved risk signals to event-driven, engineering-owned pipelines.
What I did
Built a credit limit service and a fraud-labelling service from scratch.
Replaced synchronous calls between Risk and Refinancing with an event-driven credit score for Pan-European refinancing.
Moved real-time fraud features from Data Science to Engineering.
Led EDA 2.0 across 12 repositories and set shared CI and code standards for the Risk team.
4SumUp, BerlinJun 2019 – Nov 2023
Senior Software Engineer
Built shared backend foundations: a service template, a money library used across backend and Android, and large data migrations.
Cut new service setup from a week to 1-2 hours with a service template.
Built the money library shared by SumUp's backend and Android apps, and the authorization and permissions libraries for point-of-sale services.
Migrated 6 years of historical data with minimal production impact.
4
SumUp, Berlin, GermanyJun 2019 – Nov 2023
Senior Software Engineer
Built shared backend foundations: a service template, a money library used across backend and Android, and large data migrations.
What I did
Cut new service setup from a week to 1-2 hours with a service template.
Built the money library shared by SumUp's backend and Android apps, and the authorization and permissions libraries for point-of-sale services.
Migrated 6 years of historical data with minimal production impact.
Introduced SLO monitoring and on-call rotations for critical point-of-sale services.
3NICE, Ra'ananaDec 2017 – May 2019
Backend Software Developer
Backend development on a distributed product, focused on cache performance and reliability.
Refactored a product's cache system for performance and reliability.
Built Jira-integrated release tooling in Python.
3
NICE, Ra'anana, IsraelDec 2017 – May 2019
Backend Software Developer
Backend development on a distributed product, focused on cache performance and reliability.
What I did
Refactored a product's cache system for performance and reliability.
Built Jira-integrated release tooling in Python.
2Inuitive, Ra'ananaAug 2014 – Dec 2017
C++/C# Developer
Vision-processing algorithms in C++, and production lines for the chips in South Korea and China.
Developed algorithms for vision processing chips in C++.
Set up production lines and their calibration tooling on-site in South Korea and China.
2
Inuitive, Ra'anana, IsraelAug 2014 – Dec 2017
C++/C# Developer
Vision-processing algorithms in C++, and production lines for the chips in South Korea and China.
What I did
Developed algorithms for vision processing chips in C++.
Set up production lines and their calibration tooling on-site in South Korea and China.
1Reichman University2012 – 2016
B.Sc. Computer Science
Courses, degrees, and topics that keep showing up in the work.
Advanced Software Architecture Workshop with Residuality Theory (2024)
Neo4j Fundamentals (2024)
Software Architecture & Design (2023)
Design Patterns (2022)
1
Reichman University2012 – 2016
B.Sc. Computer Science
Courses, degrees, and topics that keep showing up in the work.
Teaching
Teacher Assistant to Computer Science Professor in Intro to CS · Oct 2013 – Feb 2015
Teacher Assistant to Computer Science Professor in Advanced Programming · Mar 2014 – Aug 2014
Courses and workshops
Advanced Software Architecture Workshop with Residuality Theory · Workshop, 2024 · certificate
Kotlin for Java Developers · JetBrains, 2020 · certificate
LLobbyRecommendations
What people notice after working with me.
I'd love to work with Yonatan again. Blake Irvin, Leading Observability Engineering at SumUp
the go-to person for almost any problem Oren Hadry, Former Engineering Manager at Inuitive
a highly talented and disciplined software developer Shimon Schocken, Computer Science Professor, Reichman University
Kotlin, Spring Boot, OpenAPI, Kafka, Flink, Terraform, GitHub Actions, Docker, PostgreSQL, MySQL
L
LobbyHow I work
I like the moment when a domain becomes specific enough to build.
The hard part of backend engineering is often not choosing a framework. It is finding the real boundary: which team owns the rule, which event is authoritative, what happens when a vendor disagrees, and how the next engineer will debug the failure at 2 a.m.
That is where I tend to be useful. I ask until the domain is crisp enough to model, then turn it into production code, API contracts, migration plans, dashboards, runbooks, or diagrams that survive the handoff.
I care about strong implementation, but the higher leverage is making the system easier for the whole team to operate, extend, and argue about with evidence.
Works across
Backend systems, Kotlin/JVM, service design, OpenAPI, Kafka, internal tools, docs, and OSS
Bias toward
Shared understanding, small useful abstractions, boring reliability, and explanations that survive handoff
Recommendations
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.
Blake Irvin, Leading Observability Engineering at SumUp
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.
Oren Hadry, Former Engineering Manager at Inuitive
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.
Shimon Schocken, Computer Science Professor, Reichman University
Practice Areas
Backend architectureDesigning services, contracts, and boundaries that stay understandable as systems grow.KotlinJavaSpring BootOpenAPIgRPCProtocol Buffers
Distributed systems and data flowsBuilding event-driven services, real-time processing, and the infrastructure that keeps backend systems coherent under load.KafkaFlinkNeo4jMySQLPostgreSQL
Platform and developer experienceImproving the day-to-day engineering loop through templates, CI, internal tools, and shared libraries.GradleGitHub ActionsTerraformDockerKubernetes
Observability and production trustMaking systems easier to debug, monitor, and operate when the stakes are real.OpenTelemetryNewRelicKafka DLTsRunbooks
Technical writingExplaining backend design, debugging, and implementation tradeoffs clearly enough to be useful.KotlinArchitecture notesPostmortem-style thinking
PParkingSelected work
Public work that turns repeated problems into reusable material.
Bottom of the building: the lift goes no lower. Scroll up, or ride to the roof to get in touch.
P
ParkingSelected work
Public work that turns repeated problems into reusable material.
Upstream contributions
openapi-generator · Upstream contributionUpstream Kotlin Spring generator work for Spring Boot 4, Jackson 3, Retrofit compatibility, and regression coverage across generated server/client code.Case study · GitHubKotlinSpring BootOpenAPI
Konsist · Upstream contributionUpstream Kotlin static-analysis work spanning null-aware type matching, snippet verification, and CI pipeline discipline.Case study · GitHubKotlinStatic analysisCI
ff4j · Upstream contributionUpstream Jakarta namespace migration work that exposed the release gap behind the later ff4k replacement.Case study · GitHubJavaJakarta
java-design-patterns· Upstream contributionRefactored the Prototype pattern implementation.
Java
Libraries and tools
ff4k · Open source libraryA Kotlin Multiplatform feature flag library built to replace a stalled Java-era dependency with typed APIs, async storage, and coroutine-aware targeting.Case study · DocsKotlinMultiplatformCoroutines
TaleKeeper · Self-hosted toolA self-hosted tabletop RPG memory tool that turns local session audio into transcripts, speaker-aware review, summaries, and searchable campaign records.Case study · DocsPythonFastAPISvelte
sse-mcp-server · AI-agent infrastructureA Spring Boot Kotlin MCP bridge that exposes typed tools over Server-Sent Events for Flowise-style agent workflows.Case study · GitHubKotlinSpring BootMCPSSEDocker
kotlin-design-patterns· Technical writing / docsSoftware design patterns implemented in idiomatic Kotlin. A teaching/reference project that turns familiar object-oriented patterns into Kotlin-first examples with a generated …KotlinMkDocs
poor-life-choices· Small productMead sharing app for friends. JavaScript/React, live on Vercel.
ReactJavaScriptVercel
xkcd-click-and-drag· Data reconstructionFull image reconstruction of the famous XKCD comic #1110 using Kotlin.
Kotlin
Beat The Machine· University projectAI-powered guessing game where players identify prompts used to generate images. Built as a university project, later rewritten with DDD.
KotlinSpring BootDDD
Games
Emma's Inferno· GameAtmospheric puzzle-platformer exploring themes of morality. University capstone project.
UnityC#
Larry the Last Zombie· GameTower defense game. Team project at Reichman University.
UnityC#
Jacob's Choice· Awarded gameHorror adventure game. Won 3rd place at GameIS Awards 2015.
GameMakerGML