Olaf Kloecker, Developer in Edinburgh, United Kingdom
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Olaf Kloecker

Verified Expert  in Engineering

Full-stack Developer

Edinburgh, United Kingdom
Toptal Member Since
April 1, 2016

Olaf is a full-stack Java developer who has come a long way since writing his first programs with Turbo Pascal on a handed-down home-built CP/M 80 system. He is a certified GIAC Secure Software Programmer-Java. Olaf likes to write robust, secure software running commercially in motorway toll collection systems, navigation devices, and security management platforms. A special interest of his is language processing.


Bootstrap, CSS3, Back-end, Git, Linux, Web Development, Redux, REST APIs...
Gepalon Networks Ltd (via Toptal)
React, Node.js, MongoDB, PostgreSQL, Jitsi, Front-end, HTML5, React Redux, CSS...
Brightpunch, Ltd. (via Toptal)
Jitsi, CSS3, CSS, HTML5, Back-end, Git, Linux, Node.js, Web Development, Redux...




Preferred Environment

Bash, Vim Text Editor, IntelliJ IDEA, Windows, Linux

The most amazing...

...thing I've researched and coded is a grapheme-to-phoneme converter using an artificial neural net.

Work Experience

Freelance Senior Full-stack Developer

2017 - PRESENT
  • Architected hardware and software infrastructure and technologies.
  • Transformed a given design into a fully functional single-page REST-backed web application.
  • Implemented all parts of the front end, including maps, using React and related libraries, including different roles, user, admin, and external developer dashboards.
  • Wrote green papers on the infrastructure. Opened the API for external developers, performance, and security improvements.
  • Set up AWS Linux servers and deployed the back end, front end, and dependencies, including NGINX and firewalls.
  • Engaged in problem analysis on the front end, back end, a MongoDB database, and servers.
  • Extended the Node.js back end with new functionality, improved the codebase, and fixed memory leaks.
  • Improved efficiency through the introduction of microservices, parallelization of operations, and Redis in-memory data caching.
  • Updated the dependencies to the newest versions continually.
  • Transformed the codebase to use ES6 Promises instead of callbacks. Refactored code into TypeScript to integrate into the wider company software landscape.
Technologies: Bootstrap, CSS3, Back-end, Git, Linux, Web Development, Redux, REST APIs, Full-stack, CSS, HTML5, Loopback, Node.js, Socket.IO, JavaScript, Redux-Saga, React, Redis, APIs, MongoDB, MongoDB Atlas, ES6 Promises, Front-end, React Redux, Express.js, Bash, Debugging, REST, Bash Script, Bug Analysis & Reporting, MERN Stack, TypeScript, Axios, Vanilla JS, Jest, Leaflet, Maps, Databases, Full-stack Development, API Integration

Front-end Developer for Medical Streaming and Analysis App

2020 - 2021
Gepalon Networks Ltd (via Toptal)
  • Extended the Jitsi Meet platform to integrate artificial intelligence (neural network) generated image inference to highlight body tissue parts in a live video stream.
  • Configured and integrated Prosody modules of Jitsi Meet platform to allow token-based video conference sessions and record join end times.
  • Created Node.js and Express-based back end to store session and user information in PostgreSQL database.
  • Created user and admin dashboards to handle user meta information in relation to Jitsi Meet sessions.
  • Created Node.js back end to run TensorFlow inference as a REST service.
Technologies: React, Node.js, MongoDB, PostgreSQL, Jitsi, Front-end, HTML5, React Redux, CSS, CSS3, Debugging, REST, ES6 Promises, Tailwind CSS, Express.js, Axios, Vanilla JS, Databases, Full-stack Development, API Integration

Senior Front-end Engineer

2020 - 2020
Brightpunch, Ltd. (via Toptal)
  • Extended the Jitsi Meet video conferencing platform to allow participants to cooperatively draw with their mouse over the moderator's video stream after being granted permission.
  • Added a custom toolbar containing shape, color, line width choosers, and undo, redo, and clear session control buttons.
  • Leveraged an internal message passing facility using a custom message format.
  • Created a CSS/JavaScript-line width chooser to use alongside the color chooser.
Technologies: Jitsi, CSS3, CSS, HTML5, Back-end, Git, Linux, Node.js, Web Development, Redux, REST APIs, Full-stack, HTML5 Canvas, JavaScript, React, Front-end, React Redux, Debugging, ES6 Promises, Tailwind CSS, Express.js, Axios, Vanilla JS, Databases, Full-stack Development, API Integration

Web Developer

2017 - 2017
  • Created a responsive web page for mobile devices on the basis of a desktop site.
Technologies: CSS, HTML5, Back-end, Git, Linux, React, Web Development, Redux, Full-stack, JavaScript, CSS3, Jinja, REST APIs, Front-end, React Redux, REST, Redux Thunk, ES6 Promises, Axios, Vanilla JS, Databases

Freelance Senior Java Developer | Freelance Consultant

2016 - 2017
TradeReplay (via Toptal)
  • Consulted with clients on which technologies to use, cloud platforms, and payment providers.
  • Created the hardware and software architecture, data model, and overview diagrams for the web-based self-service members' area of a standalone desktop app to provide functionalities for registration, profile change, subscription change as well as the administrative area.
  • Developed the members' area based on Play Java with Twirl templates and Ebean ORM to PostgreSQL database.
  • Installed a system and documented the setup on a Linux server—integrating WordPress for a third-party-provided public promotional website.
  • Communicated with clients regularly, mainly through Asana, but also through email and phone—providing weekly progress reports.
Technologies: Back-end, Play, Git, Web Development, REST APIs, Full-stack, NGINX, Linux, PostgreSQL, Bootstrap, Java, Play Framework, Front-end, REST, Databases, Full-stack Development, API Integration

Freelance Architect | Freelance Developer

2016 - 2017
Freelance Work
  • Architected and single-handedly developed Trunksta.de, a social-sharing platform for sending items in other people's cars.
  • Developed the front end as a single-page application with React/Redux.
  • Implemented the back end with the Lightbend Play Java framework with an Nginx reverse proxy/load balancer and PostgreSQL database mapped to Java entities through Ebean-ORM.
  • Specified infrastructure requirements and installed the system on Linux servers.
Technologies: Back-end, Git, Java, Play Framework, PostgreSQL, React, Databases, Full-stack Development

Service Consultant

2015 - 2015
Cellent AG (Fellbach, Germany)
  • Provided second- and third-level support for a complex legacy web-based project-management system in the automotive industry spanning a variety of frameworks and technologies.
  • Acted as the main customer contact for a major component.
  • Coordinated incident support, maintained systems, performed analysis, and fixed bugs.
  • Analyzed error reports from clients and fixed bugs.
  • Managed the database data and structures through manual SQL commands.
Technologies: Back-end, Confluence, Jira, Apache Struts, Jakarta EE, Java, Code Review, Databases

Software Development Engineer

2013 - 2014
Dell Inc./Dell SecureWorks (Edinburgh, UK)
  • Extended and maintained complex, robust, and secure business-critical software systems for managed security services and counter-threat units.
  • Fixed bugs in a legacy Perl application for manual and automatic device maintenance.
  • Documented all parts of the newly built systems.
  • Took part in daily scrum sessions.
  • Performed user acceptance testing for newly developed features.
  • Certified as a GIAC Secure Software Programmer-Java (GSSP-Java).
  • Certified as a Cloudera Certified Developer for Apache Hadoop (CCDH).
Technologies: Back-end, Scrum, Full-stack, OpenGrok, iBATIS, MyBatis, Confluence, Jira, FindBugs, Apache Tomcat, Ext JS, Apache Maven, Perl, Bash, Linux, Java, Code Review, Bash Script, Databases

Software Engineer

2006 - 2013
TomTom Software Ltd (Edinburgh, UK)
  • Supported the maintenance and improvement of the in-house continuous integration system for automated tests.
  • Created a tool to visualize a large number of trip logs into global and regional traffic heat maps.
  • Supported a navigation device platform development through testing of WebKit, automatic route testing, and embedded testing/debugging.
  • Created sample Android apps for current navigation devices to be included in an API toolkit for third parties extending the platform (e.g., Renault R-Link).
  • Developed an SVN/Maven repository crawler to check for project health, inconsistencies, missing information, prevent bit rot, ensure buildability, detect dependency cycles, and identify logical build sequences.
  • Created a RESTful web back end for a prototype device to store/retrieve data; implemented automatic tests.
  • Ported a WebDAV server from C++ to Java.
Technologies: Back-end, JavaScript, Ajax, Apache HTTP Server, HTML, Jenkins, Apache Maven, Android, Bash, Linux, Java, Code Review, Bash Script, TestNG, Maps, Databases

Professional Systems Engineer

2001 - 2005
T-Systems GEI GmbH (Bonn, Germany)
  • Developed a GIS application to convert a detailed digital street map into an abstract motorway graph, processing highly-complex temporally-changing data structures with graph algorithms.
  • Created a GUI program for GIS visualization of road maps.
  • Built a back end of a web booking system for toll tickets including PDF creation.
  • Supported new and junior team members to get acquainted with software.
  • Introduced static metrics (metrics, code coverage, dependency analyses) into the build lifecycle.
  • Wrote the end-user documentation for the GUI application.
Technologies: Back-end, AWT, Swing, PDF, XML, HTML, UML, CSV, Ant Design, JUnit, JDBC, SQL, Java, Code Review, Maps, Databases

Unix/Linux Systems Administrator

1998 - 2001
Tops.net GmbH & Co. KG (Bonn, Germany)
  • Supported and extended a Linux-based internet dial-up server for SoHo companies.
  • Created the back end of a document management system converting SGML documents into PDF files via LaTeX.
  • Managed client servers and networks.
  • Set up and installed Linux-based servers.
Technologies: LaTeX, Perl, Bash, Unix, Linux, Bash Script

Memo Molecule

I developed a responsive web app to create email reminders with powerful recurrence rules like "every last working day of the month" or "every third Saturday," taking into account local time zones.

It was built with React on the front end and Node.js (Loopback/Express.js) on the back end with a MongoDB database. It also uses Semantic UI for styling and has multi-language support built in.

WeatherWorks Advantage

I built a forecast management system for winter and non-winter events comprising a complex React user and admin dashboards, report pickup pages and a Node.js back end backed by a MongoDB database.

TRUNKSTA.DE | Social Sharing Platform

Sole (software and infrastructure) architect and full-stack developer of a social sharing platform (no design) for the German market. Built with React.js and Redux on the front end and Java Play/PostgreSQL/Nginx on the back end. It includes all aspects of a platform including user authentication, management, admin functions, transaction email, PayPal integration, and business logic. I heavily relied on Play's reactive features, and Java 8 structures (collection streams, Optionals, and Lambdas).

Launched in December 2016.


I developed a data-driven, artificial neural network-based grapheme-to-phoneme converter for Scottish Gaelic (not yet available online).

Faclair Dictionaries and Grammar

These are Scottish Gaelic/English/German dictionaries and a concise grammar text for the Scottish Gaelic language, available as Kindle e-books.


JavaScript, Java, HTML, HTML5, CSS, Bash Script, XML, UML, CSS3, Bash, SQL, Perl, TypeScript


Redux, Express.js, Vanilla JS, Loopback, React Native, Play, TestNG, JUnit, Tailwind CSS, Ant Design, Apache Struts, Play Framework, Bootstrap, Jinja, Ext JS, Swing, Hadoop, iBATIS, Jest


REST APIs, Redux-Saga, React, Node.js, JSON API, React Redux, Leaflet, Ebean ORM, AWT, HTML5 Canvas, Socket.IO, Java Security, SLF4J, MyBatis, JDBC


Redux Thunk, Confluence, Jira, LaTeX, Git, IntelliJ IDEA, Subversion (SVN), Eclipse IDE, Vim Text Editor, Apache HTTP Server, Apache Tomcat, NGINX, Jenkins, Sonar, Mercurial, Perforce, Apache Ant, Apache Maven, MongoDB Atlas, AWS IAM


REST, Agile Software Development, Object-oriented Design (OOD), Scrum


JSON, MySQL, MongoDB, PostgreSQL, Databases, Redis, Amazon DynamoDB, Amazon S3 (AWS S3)


Debugging, Bug Analysis & Reporting, Web Development, Full-stack, Front-end, Front-end Development, Back-end, APIs, MERN Stack, Axios, Maps, Full-stack Development, API Integration, Germany, Code Review, Semantic UI, CSV, PDF, OpenGrok, Ajax, FindBugs, GUI Development, TCP/IP, Jitsi, ES6 Promises, Amazon API Gateway


Kindle, Linux, Windows, Unix, Jakarta EE, Google App Engine, Java EE, Android, Amazon Web Services (AWS), AWS Cloud Computing Services, Amazon EC2, AWS Lambda

1993 - 2001

Master of Arts Degree in Phonetics, Speech Signal Processing, Computational Linguistics, Computer Science, and Celtic Languages

University of Bonn - Bonn, Germany

MARCH 2024 - MARCH 2027

AWS Certified Developer - Associate

Amazon Web Services Training and Certification

MAY 2014 - MAY 2018

GIAC Secure Software Programmer - Java, GSSP-Java


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