Janos Breuer, Developer in Budapest, Hungary
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Janos Breuer

Bio

Janos is an AI application engineer with 17+ years of experience building production software in finance, SaaS, and regulated domains. For Goode Capital, he delivered production-trading systems, including exchange-market data, a real-time Excel add-in, and Node.js and WebSocket sync for live traders. Janos built an AI agent platform with RAG, tool use, and citation-aware outputs for legal workflows. Clients value his clear communication, pragmatic architecture, and production-first delivery.

Portfolio

Goode Capital
API Integration, Trading, QuickFIX, Trading Systems, Finance APIs, FIX Protocol...
Realeyes
SWIG, Android NDK, Amazon Kinesis, Retrofit, Kotlin, Android, Coroutines...
W.UP
Jenkins, Kotlin, Android, Android Studio, Test-driven Development (TDD)...

Experience

  • APIs - 10 years
  • Java - 8 years
  • Android - 5 years
  • Node.js - 3 years
  • TypeScript - 3 years
  • OpenAI API - 1 year
  • Retrieval-augmented Generation (RAG) - 1 year
  • AI Agents - 1 year

Preferred Environment

Windows, Git, MacOS, TypeScript, Node.js, Python, React, PostgreSQL, LangChain, OpenAI API

The most amazing...

...MVP I built with practicing lawyers is an AI agent for legal research over legislation and court rulings, focused on citation-backed, auditable outputs.

Work Experience

Full-stack Engineer

2024 - 2026
Goode Capital
  • Built and maintained production trading systems for a London-based oil trading firm, including a FIX adapter for ICE exchange connectivity and an Excel add-in for real-time desk pricing.
  • Delivered TypeScript/Node.js WebSocket sync between exchange market data feeds and trader Excel workflows used daily on the desk.
  • Deployed the FIX adapter and Excel pricing add-in on AWS; built a pricing history database to persist and query pricing data for the add-in.
  • Integrated QuickFIX/J for live exchange connectivity and supported the production environment with traders and the ops team.
Technologies: API Integration, Trading, QuickFIX, Trading Systems, Finance APIs, FIX Protocol, TypeScript, Node.js, WebSockets, React, Amazon RDS, Amazon Web Services (AWS)

Senior Mobile Developer

2020 - 2023
Realeyes
  • Implemented a digital well-being app with Jetpack Compose UI and clean architecture.
  • Wrote a wrapper SKD for a native emotion detection component.
  • Implemented REST API session handling and integrated Amazon Kinesis SDK.
  • Designed RxJava interfaces for internal components of the SDK.
Technologies: SWIG, Android NDK, Amazon Kinesis, Retrofit, Kotlin, Android, Coroutines, Jetpack Compose, Swagger, Android Studio, Test-driven Development (TDD), Android SDK, Design Patterns, Unit Testing, JPA, Gradle, Dependency Injection, JNI, Automation, SDKs, Clean Architecture, Firebase, Push Notifications, REST APIs, APIs

Senior Mobile Developer

2017 - 2020
W.UP
  • Developed mobile banking Android applications for several European banks, e.g., Cembra.
  • Built complex UIs with theming, as well as the foundation of the business logic, so that it adheres to clean architecture.
  • Integrated a mobile payment service to one of the apps.
  • Held test-driven development presentations and workshops for my team.
Technologies: Jenkins, Kotlin, Android, Android Studio, Test-driven Development (TDD), Android SDK, Retrofit, Spring, Spring Boot, Spring MVC, Design Patterns, Unit Testing, Gradle, Dependency Injection, Automation, Clean Architecture, Firebase, Push Notifications, Technical Leadership, REST APIs, APIs

Android Developer

2014 - 2016
LogMeIn
  • Developed two apps and an SDK for Android as part of the mobile scrum team at LogMeIn Rescue. These applications are integral components of a large-scale SaaS application used for remote support by companies like Microsoft and Vodafone.
  • Used a wide range of Android system features to remotely control and diagnose a device.
  • Refactored the remote control component so that it could be unit-tested.
Technologies: WebRTC, JNI, Retrofit, Android SDK, Android Studio, Test-driven Development (TDD), Android NDK, Design Patterns, Unit Testing, Gradle, Dependency Injection, Automation, SDKs, REST APIs, APIs

Full-stack Developer

2011 - 2016
MuTrader.com
  • Developed a real-time financial mobile app for iOS and Android with a back-end server that had push notifications and an integration to 3rd-party Forex broker systems.
  • Implemented the back end with service-oriented architecture and a RESTful API.
  • Used enterprise integration patterns and FIX protocol to connect to brokers.
  • Wrote unit tests and automated acceptance tests with TDD.
Technologies: QuickFIX, FIX Protocol, Apache Camel, Hibernate, Spring, Retrofit, Android SDK, Android Studio, Test-driven Development (TDD), Spring Boot, Spring MVC, C#, iOS, Design Patterns, Unit Testing, JPA, Enterprise Integration Patterns (EIP), Dependency Injection, Angular, MySQL, Azure, Push Notifications, Technical Leadership, REST APIs, APIs, Trading Systems, Finance APIs, Finance

Lead Software Engineer

2011 - 2013
LogMeIn
  • Led a team of 7-9 engineers in the development of two Windows client components for LogMeIn Rescue.
  • Acted as a member of the company-wide architecture review board.
  • Interviewed new developer candidates and participated in the hiring decisions.
  • Created a code-branching policy and introduced code reviews, which stabilized the release process of the component.
  • Evangelized unit-testing and test-driven development (TDD); also organized TDD training sessions for the team.
  • Created the system design and a prototype for the planned rewrite of a client component for four platforms (Windows, Mac, Android, and iOS).
Technologies: SOAP, ATL, C++, Test-driven Development (TDD), Windows, UML, Design Patterns, Unit Testing, Win32, Technical Leadership, APIs

Software Engineer

2007 - 2011
LogMeIn
  • Collaborated with the C++ team at LogMeIn Rescue to develop a browser plugin using SOAP, STL, and ATL.
  • Implemented major features in the Windows component of the product, including technician collaboration and unattended access.
  • Implemented a task-based threading model that allowed the team to eliminate frequent bugs related to deadlocks and UI freezes.
  • Answered level 3 support requests, troubleshooting urgent technical issues with VIP customers.
  • Presented to 100+ developers at a company conference about my team's achievements.
Technologies: SOAP, ATL, C++, Windows, UML, Design Patterns, Unit Testing, Win32, APIs

Software Engineer

2006 - 2007
Lufthansa Systems
  • Developed an airline schedule optimizer in a distributed team, communicating daily with remote team members.
  • Implemented and unit-tested graph data structures and algorithms in C++ on four Unix variants.
  • Refactored our unit-testing framework, significantly reducing the size of unit test binaries and saving storage-related costs.
Technologies: Linux, Unix, C++, UML, Design Patterns, Unit Testing, Algorithms

Experience

Legal AI Agent for Research & Submission Workflows

Built a citation-first legal AI agent for professional workflows. The agent helps lawyers draft submissions and develop argument strategies while researching authoritative sources. It retrieves relevant legislation with precise references and finds matching court decisions from public legal sources.

The experience works like an IDE for legal research: practitioners chat with the agent and open cited sources, including PDFs, directly from the conversation. Answers are source-grounded and structured for professional review.

It is co-developed with practicing lawyers through customer discovery on a representative sample matter. The architecture combines RAG over public sources, tool-using agent workflows, and iterative retrieval and prompt design toward reliable legal research assistance.

Mindfully App

Created a digital well-being application with a user base exceeding 50,000 downloads, focused on monitoring and analyzing facial expressions during mobile phone usage to provide insights into the emotional impact of technology usage.

In this role, I spearheaded the rewrite of an SDK to encapsulate the image recognition component, facilitating emotion detection in 3rd-party apps.

Collaborating closely with a team of two developers, I introduced advanced theming techniques using Jetpack Compose. Additionally, I successfully advocated for the implementation of clean architecture principles, thereby ensuring the scalability and maintainability of the project.

Cembra Mobile Bank

I developed the Android mobile bank client application for Cembra, a Swiss credit card bank.

I used state-of-the-art architecture and technologies in this project, such as biometric authentication, clean architecture, reactive programming, and dependency injection.

LogMeIn Rescue

https://play.google.com/store/apps/details?id=com.logmein.rescuemobile&hl=hu
LogMeIn Rescue is a SaaS platform used by millions to get remote support from tech support companies and software vendors such as Microsoft and Vodafone. I worked on the Android app and the Windows client and designed several features as an architect.

As the lead developer of a team of 7-9 engineers, I implemented a code branching policy and pioneered a code review process. These initiatives improved code quality, enhanced knowledge sharing, and stabilized release processes for the component.

Rescue Lens

https://play.google.com/store/apps/details?id=com.logmein.rescuelens&hl=hu
The Rescue Lens app for Android allows support agents to use the camera on the user's Android device to see what they are seeing.

I implemented several features in the app and planned and performed a major refactoring that made the code more robust and maintainable.

Stack Overflow Contributions

As a personal project, I answered several questions on Stackoverflow.com related to Android development. That allowed me to learn to express ideas in a clear and concise way, and also to learn more about specific topics related to Android development.

MuTrader

https://drive.google.com/file/d/1ghKMfI-Ty0uEZWN-PQOttVQ-D7Dui6z8/view
MuTrader is a financial mobile app for iOS and Android with a back-end server with push notifications and integration to 3rd-party Forex broker systems.

It connected Forex advisers, traders, and brokers.

Education

2001 - 2006

Master's Degree in Mathematics

Budapest University of Technology and Economics - Budapest, Hungary

Skills

Libraries/APIs

Retrofit, REST APIs, WebRTC, ATL, Node.js, React, OpenAI API

Tools

Android Studio, Gradle, Jenkins, Git, Android NDK, SWIG, GitHub, AWS ELB

Languages

Java, Kotlin, C++, UML, C#, Bash Script, TypeScript, Python

Frameworks

Android SDK, Swagger, Spring Boot, Spring, Spring MVC, Apache Camel, JNI, JPA, Hibernate, Angular, Electron

Paradigms

Test-driven Development (TDD), Design Patterns, Dependency Injection, Unit Testing, Automation, Clean Architecture

Platforms

Android, Windows, Linux, Firebase, Unix, iOS, Azure, Win32, MacOS, Amazon Web Services (AWS)

Storage

MySQL, PostgreSQL

Industry Expertise

Trading Systems

Other

APIs, Algorithms, Push Notifications, Technical Leadership, WebSockets, SOAP, Amazon Kinesis, QuickFIX, Enterprise Integration Patterns (EIP), FIX Protocol, Mathematics, Coroutines, Jetpack Compose, SDKs, Finance APIs, Finance, LangChain, AI Agents, Retrieval-augmented Generation (RAG), Large Language Models (LLMs), API Integration, Trading, Amazon RDS, Tools, AI Development

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