Bjorn Stiel, Developer in London, United Kingdom
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Bjorn Stiel

Verified Expert  in Engineering

Software Developer

London, United Kingdom
Toptal 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.


Python, Microsoft Excel
Freelance Financial Technology Consulting
Python, APIs, Trading, Finance, Data Processing, Integration, Algorithms...
Credit Suisse
C#, Python, Trading, APIs, Finance, Data Processing, Integration, Algorithms...




Preferred Environment

Windows, Linux, Docker, Visual Studio Code (VS Code)

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

Work Experience

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, Microsoft Excel

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, Trading, Finance, Data Processing, Integration, Algorithms, Investments, Investment Manager

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, Trading, APIs, Finance, Data Processing, Integration, Algorithms, Investments, Investment Manager, Microsoft Excel, Options Trading, Algorithmic Trading, Backtesting Trading Strategies

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, Trading, APIs, Finance, Data Processing, Integration, Algorithms, Investments, Investment Manager, Microsoft Excel, Options Trading, Algorithmic Trading, Backtesting Trading Strategies

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: Microsoft Excel, Finance, Algorithms

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 multitenant cloud) deployment process.

xlwings | Python for Excel
xlwings is an open-core spreadsheet automation package with a beautiful API. xlwings makes it easy to call Python from Excel and vice-versa and is an alternative to VBA macros/UDFs and Power Query. xlwings works across Excel on Windows and macOS, Excel on the web, and Google Sheets.

Trading and Execution System

A Python-based trading and execution system for US equities. As an architect and lead developer, I integrated 3rd-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.
2006 - 2008

Master's Degree in Financial Engineering

Birkbeck College, University of London - London, United Kingdom

2000 - 2005

Master's Degree in Business Economics

Free University of Berlin - Berlin, Germany


SQLAlchemy, Bloomberg API, Interactive Brokers API, Pandas


Celery, Git, Microsoft Excel, Excel-DNA, Docker Compose, Visual Studio Tools for Office (VSTO), Pytest


Flask, Django, Django REST Framework


Python, Falcon, Excel VBA, Visual Basic, Visual Basic for Applications (VBA), SQL, C#


Docker, Jupyter Notebook, Visual Studio Code (VS Code), Linux, Windows, Kubernetes




xlwings, Trading, Trading Applications, APIs, API Integration, Web Scraping, Finance, Data Processing, Integration, Investments, Investment Manager, Back-end, Data Analysis, Options Trading, Algorithmic Trading, Backtesting Trading Strategies, Algorithms, LDAP

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