Robert-Jan Mahieu, Developer in Leiderdorp, Netherlands
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Robert-Jan Mahieu

Verified Expert  in Engineering

Back-end Developer

Leiderdorp, Netherlands
Toptal Member Since
November 5, 2021

Robert-Jan is a back-end developer with 13 years of experience. He recently helped scale a Dutch fintech startup from the first lines of code to unicorn status. Robert-Jan is exceptionally skilled at quickly finding his way in new platforms or APIs and database design and performance optimization. He takes ownership, delivers on time, and aims for the best possible outcome in any given scenario.


PHP, REST APIs, MySQL, Apache, Ubuntu, Software as a Service (SaaS)...
PHP, MySQL, Amazon Athena, Amazon Aurora, REST, APIs, Payment APIs...
Java, Oracle, PL/SQL




Preferred Environment

MacOS, PhpStorm, PHP, MySQL, Vue, JavaScript, Apache2, Git, Amazon Web Services (AWS)

The most amazing...

...thing I've done is to help a fintech startup scale from the very first lines of code to unicorn status.

Work Experience

Founder | Software Engineer

2021 - PRESENT
  • Founded my own company as a solo entrepreneur offering SaaS solutions.
  • Built a flexible and custom back-end framework in PHP to use as a starting point for any SaaS.
  • Launched multiple products in quick succession,,, and
Technologies: PHP, REST APIs, MySQL, Apache, Ubuntu, Software as a Service (SaaS), Architecture, APIs, Search, Documentation

Principal Back-end Developer

2014 - 2021
  • Built the core backing architecture for the back end from the first lines of code and scaled it from zero to a payment volume of €40 billion a year.
  • Migrated the entire back-end API and database from private servers to AWS cloud infrastructure with less than one-hour downtime.
  • Designed, implemented, and coordinated multiple payment systems in record time, with market-leading partners such as Mastercard, EBA Clearing, Wise, and
  • Implemented and designed onboarding flows with advanced KYC.
  • Analyzed usage data to help detect phishing, fraud, or money laundering and implemented measures to combat this.
  • Invented a communication protocol for which a US patent was granted.
Technologies: PHP, MySQL, Amazon Athena, Amazon Aurora, REST, APIs, Payment APIs, Card Payments, Online Banking, Mobile Payments, Git, SOAP, GitLab CI/CD, GitLab, XML, JSON, SQL, Databases, RDBMS, Back-end Development, Back-end Architecture, Back-end Performance, Mobile Back-end, Architecture, Apple Push Notifications, Amazon Web Services (AWS), Back-end, Clean Code, Code Review, IT Deployments, Build Releases, Release Management, Sentry, Mastercard, Credit Cards, Bootstrap, Test-driven Development (TDD), Docker, MariaDB, Twilio API, Twilio

Software Developer

2009 - 2013
  • Implemented new features and bug fixes in a B2B trading platform.
  • Wrote tools to help developers throughout the company perform their work more effectively and save time.
  • Achieved certification after extensive training in stock markets and associated theory relevant to the retail brokerage business of the company.
Technologies: Java, Oracle, PL/SQL

Junior Software Developer

2008 - 2009
Alex Vermogensbank
  • Resolved many memory leaks in the Delphi code of the back-end of a service-oriented architecture (SOA).
  • Was promoted from junior to medior in just six months.
  • Refactored the code for the yearly trading reports for end-users from the old deprecated platform to the newly introduced codebase and coding standards.
Technologies: Delphi, Oracle, PL/SQL, Message Queues, Service-oriented Architecture (SOA) - Application Monitoring Software

A platform designed to monitor uptime, page speed insights, and track both errors and user behavior. It also has advanced notifications for all of the above, both through email and browser push to Chrome or Safari. Stripe payments are integrated, as well.

I designed and built every aspect, from front-end design, with a back-end API to server maintenance. The project took two weeks from the initial idea to public launch.


A platform to assist lawyers with jurisprudence research for the Dutch market. The system retrieves all court rulings published on different sources and parses them into a single database to make them easily searchable through a user-friendly interface.

The entire project (back end and front end, including UI/UX design) was developed by me in less than two months from the first idea to the public launch.

Built a front end and back end for a platform to compare political parties for the Dutch national elections of March 2021. I wrote code to parse the PDF manifesto of each party and save it into a database for easy comparison.


PHP, PHP 7, XML, SQL, JavaScript, HTML, Java, CSS, Delphi, C++, Python


Twig, Tailwind CSS, Laravel, CodeIgniter, Bootstrap, Symfony


REST APIs, Vue, Stripe, Stripe API, Twilio API, Node.js


PhpStorm, Git, Apple Push Notifications, GitLab, Amazon Athena, Apache, GitLab CI/CD, NPM, Sentry


REST, Clean Code, Back-end Architecture, Service-oriented Architecture (SOA), Test-driven Development (TDD)


MacOS, Apache2, Oracle, Amazon Web Services (AWS), Ubuntu, Twilio, Docker


MySQL, Amazon Aurora, Databases, JSON, RDBMS, PL/SQL, Redis, Elasticsearch, MariaDB


Computer Science, APIs, Payment APIs, Card Payments, Online Banking, Mobile Payments, Performance Tuning, Back-end, Mobile Banking, Payment Processing, Payment Security, Payment Networks, Fintech, SOAP, API Integration, Software as a Service (SaaS), Back-end Development, Back-end Performance, Mobile Back-end, SEO Audits, Full-stack, Scripting Languages, Message Queues, Architecture, Search, Documentation, PDF, Front-end, Code Review, IT Deployments, Build Releases, Release Management, Mastercard, Credit Cards

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