Sebastiaan Janssen
Copenhagen, Capital Region of Denmark
Summary
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RockstarSebastiaan Janssen is a pragmatic back-end software engineer based in Copenhagen with 13 years of experience delivering stable, maintainable .NET systems. He contributes to high-profile open-source projects like Umbraco CMS and the win-acme ACME client, focusing on core backend maintenance, merging complex changes, and improving plugin and CLI workflows. He also brings automation and build-hardening experience from work on ImageProcessor, resolving runtime issues and modernizing build pipelines. Known for quietly improving developer experience and reliability, he excels at conflict resolution in large codebases and pragmatic refactors that reduce operational pain. Comfortable across maintenance, tooling, and automation, Sebastiaan blends hands-on coding with a steady focus on long-term stability and observability. Off the beaten path, he’s active on Mastodon, signaling an interest in decentralized social tech and community engagement.
13 years of coding experience
Stackoverflow
5,890reputation
587kreached
86answers
22questions
Github Skills (33)
nuget10
umbraco10
git10
image-processing10
letsencrypt10
net10
dotnet10
batchfile10
acme10
plugin10
netframework10
merge10
asp-net10
automation10
script10
Programming languages (14)
Github contributions (5)
umbraco/Umbraco-CMS
Sep 2012 - Dec 2022
Umbraco is a free and open source .NET content management system helping you deliver delightful digital experiences.
Role in this project:
Back-end Developer
Back-end DeveloperContributions:151 reviews, 4214 commits, 3007 PRs in 10 years 4 months
Contributions summary:Sebastiaan appears to be focused on maintaining and updating the Umbraco CMS, specifically by merging and integrating different code branches. Their work involves integrating version updates and resolving conflicts in code, which often involves changes to internal files related to data structures. The user's activity mostly revolves around managing code merging and integrating newer codebase versions. The user's contribution appears primarily focused on the core .NET backend code, ensuring it aligns with the features of this CMS system.
cmscontent-management-systemheadless-cmsaspumbraco
win-acme/win-acme
Aug 2016 - Feb 2018
A simple ACME client for Windows (for use with Let's Encrypt et al.)
Role in this project:Back-end Developer
Back-end DeveloperContributions:2 releases, 29 commits, 20 PRs in 1 year 6 months
Contributions summary:Sebastiaan primarily contributed to the development of the win-acme client, focusing on features related to plugin functionality. Their work included enabling unattended runs for custom plugins, refactoring plugin handling, and refining the command-line interface for plugin selection and operation. They added features like specifying signer emails on the command line and addressed issues related to plugin execution. The user also improved the overall code quality, comments and added Serilog for more effective logging.
letsencryptexchangerdswindowsssl
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