Bjorn Stiel, Software Developer in London, United Kingdom
Bjorn Stiel

Software Developer in London, United Kingdom

Member since February 25, 2020
Bjorn is a senior Python developer who spent over a decade building robust and scalable applications for clients such as Credit Suisse. He specializes in distributed workflows via Celery and REST APIs using Django, Flask, and Falcon. He developed an app for UBS Investment Bank that helped their trading desks manage multi-billion dollar risk. Bjorn's expertise with complex integrations prove invaluable in projects where precision matters most.
Bjorn is now available for hire



London, United Kingdom



Preferred Environment

Windows, Linux, Docker, Visual Studio Code

The most amazing... I've developed makes Excel workbook files work seamlessly with Git.


  • Technical Co-founder

    2014 - PRESENT
    • Developed a web app on top of Git that facilitates version control and collaboration for Excel.
    • Built the first iteration and brought it to market. The app is used by on-premise and Cloud customers, primarily in the financial services industry. The app supports various deployment targets: Cloud, on-premise, and airgapped on-premise and integrates with enterprise LDAP/AD systems for user (and licensed seats) management.
    Technologies: Python
  • Python Developer

    2012 - PRESENT
    Freelance Financial Technology Consulting
    • Developed bespoke Python-based solutions to a number of clients in the financial services industry (hedge funds, asset managers, trading desks), primarily in London and Zurich.
    • Built Celery-based apps for scheduling complex asynchronous workflows-long-running calculations as well as highly concurrent data flows to and from third-party systems (Bloomberg). Leveraged Django, Flask, SQLALchemy, and Falcon to deliver REST APIs.
    • Delivered containerized apps for easy CI/CD and deployment, leveraging GitLab pipelines.
    • Integrated legacy Excel/VBA applications with client-side Python code (via xlwings), server-side REST APIs and Bloomberg (via BLPAPI and Data License).
    • Integrated Django/Flask REST apps with customer's LDAP/Active Directory infrastructure for authentication and authorisation.
    • Helped customers integrate and replace Excel with Jupyter notebooks.
    Technologies: Python, APIs
  • Rapid Application Development Consultant

    2014 - 2016
    Credit Suisse
    • Developed a number of tactical Python solutions for the equity trading desks in London.
    • Integrated legacy Excel applications with modern REST APIs.
    • Spearheaded a data science project to extract historical quantitative data from non-structured data using Pandas.
    • Built various rapid application Excel/VBA applications.
    Technologies: C#, Python
  • Quant and Rapid Application Developer

    2006 - 2012
    UBS Investment Bank
    • Developed a new platform for the bank's commodity index business that enabled them to better risk-manage their complex trading book.
    • Built a Python-based backtesting platform that enabled users to rapidly prototype and launch new alpha- and beta trading strategies.
    • Oversaw and managed new product launches resulting in additional revenues to the business.
    • Introduced Excel-DNA to rapidly build Excel Add-Ins in C#, facilitating a modern integration between Excel and internal REST APIs and Bloomberg's BLPAPI.
    Technologies: C#, Python
  • Junior Risk Controller

    2005 - 2006
    Landesbank Berlin
    • Developed a suite of C++ and Excel-based tools improving the bank's ability to monitor the risk of its equity derivative portfolio.
    • Integrated internal (Murex) and external data feeds (Bloomberg) into the risk system.
    • Streamlined the department's internal RFC process to ensure a faster and higher quality release process.
    Technologies: C++, Microsoft Excel


  • Version Control and Collaboration App for Excel

    A Python-based web app that makes Excel workbooks work with Git. I was the back-end developer integrating many moving parts: Celery to do the heavy lifting and execute long-running background tasks, libgit2 for integrating Git, and Falcon to expose the REST API. The app is fully dockerized, which allows for a smooth multi-target (single-tenant on-premise and multi-tenant Cloud) deployment process.

  • xlwings - Python for Excel

    xlwings is an open-source Python library that makes it easy to call Python from Excel and vice-versa. It is developed on top of Git, facilitating version control and collaboration for Excel. The app is used by on-premise and Cloud customers, primarily in the financial services industry.

  • Trading and Execution System

    A Python-based trading and execution system for US equities. As an architect and lead developer, I integrated third-party APIs (e.g., broker-dealer), ensured that orders could be placed and amended and fills flowed back into the system, and set up accountancy and the ability to collate trade information and push it into the accounting system.


  • Languages

    Python, Falcon, Excel VBA, C#
  • Frameworks

    Flask, Django, Django REST Framework
  • Libraries/APIs

    SQLAlchemy, Bloomberg API, Interactive Brokers API
  • Tools

    Celery, Git, Microsoft Excel, Excel-DNA, Docker Compose, Pytest
  • Platforms

    Docker, Jupyter Notebook, Visual Studio Code, Linux, Windows, Kubernetes
  • Other

    xlwings, Trading, Trading Applications, APIs, LDAP
  • Storage



  • Master's Degree in Financial Engineering
    2006 - 2008
    Birkbeck College, University of London - London, United Kingdom
  • Master's Degree in Business Economics
    2000 - 2005
    Free University of Berlin - Berlin, Germany

To view more profiles

Join Toptal
Share it with others