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Sebastiaan Janssen

PROFILE

Sebastiaan Janssen

Worked extensively on the umbraco/Umbraco-CMS and UmbracoDocs repositories, delivering features and fixes that improved platform stability, cross-platform compatibility, and developer experience. Addressed build and CI reliability by refining GitHub Actions workflows and repository-scoped scheduling, while enhancing security through dependency management policies. Led terminology updates and documentation alignment for Umbraco 18, coordinating code and content changes in C#, YAML, and Markdown to support new Layout Template standards. Improved file system handling for Linux compatibility and streamlined content localization and testing infrastructure. Demonstrated depth in .NET Core, backend development, and automation, consistently focusing on maintainability, traceability, and cross-team collaboration.

Overall Statistics

Feature vs Bugs

54%Features

Repository Contributions

20Total
Bugs
6
Commits
20
Features
7
Lines of code
4,194
Activity Months8

Work History

June 2026

1 Commits • 1 Features

Jun 1, 2026

June 2026 monthly summary for UmbracoDocs focused on aligning documentation with Umbraco 18's new Layout Template terminology, completing RC3-aligned updates, and improving developer clarity and onboarding. Primary work was documentation-only, with extensive terminology updates, screenshot reshoots, and references alignment to support the RC3 backoffice context and smoother upgrade paths.

May 2026

4 Commits • 1 Features

May 1, 2026

May 2026 monthly summary for umbraco/Umbraco-CMS. Delivered two major initiatives with clear business value: (1) a Layout Template naming refresh across the codebase with tests/logging updates and backward-compatibility support, and (2) robust ShadowFileSystem improvements to address cross-platform case sensitivity. The changes reduce deployment risk, improve developer clarity, and strengthen cross-OS reliability.

January 2026

1 Commits

Jan 1, 2026

January 2026 monthly summary for development work focused on CI reliability and security in the umbraco/Umbraco-CMS project. Implemented repository-scoped gating so the scheduled GitHub Actions workflow runs only in the main repository, preventing execution on forks and reducing fork-related CI noise.

October 2025

4 Commits • 2 Features

Oct 1, 2025

Month: 2025-10 | Summary: Delivered two high-impact features for the umbraco/Umbraco-CMS repository, accelerating release communications and improving community navigation. Implemented GitHub Release Discussion Automation to auto-create and associate release discussions from release/* labels, and completed Community Website Redirects and Cleanup to centralize resources by pointing old references to forum.umbraco.com and cleaning up documentation/navigation. No major bugs fixed this month.

April 2025

1 Commits • 1 Features

Apr 1, 2025

April 2025 — Umbraco-CMS: Focused on enabling login feature development by setting up the Login Module Workspace and aligning it with the existing UI client. This groundwork accelerates upcoming authentication work and reduces integration risk by providing parallel development paths and a clear trace of work.

January 2025

3 Commits • 1 Features

Jan 1, 2025

January 2025 focused on cross-platform robustness and governance, delivering key platform hygiene improvements and policy changes that reduce platform-specific risk and strengthen security posture.

November 2024

5 Commits • 1 Features

Nov 1, 2024

Month 2024-11: Delivered targeted maintenance and stability improvements for umbraco/Umbraco-CMS, focusing on license compliance, testing infrastructure cleanup, and restoring reliable content behavior across locales. The work reduced maintenance burden, stabilized critical workflows, and preserves expected localization behavior.

October 2024

1 Commits

Oct 1, 2024

October 2024 monthly summary for umbraco/Umbraco-CMS: Delivered a targeted build stabilization fix that prevents copying of the node_modules directory during the build, addressing long-path errors and reducing unnecessary file operations across environments. The change enhances CI reliability and build performance, enabling faster feedback and more stable releases.

Activity

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Quality Metrics

Correctness93.6%
Maintainability91.0%
Architecture91.0%
Performance89.0%
AI Usage33.0%

Skills & Technologies

Programming Languages

C#JSONJavaScriptMarkdownTypeScriptXMLYAMLcshtml

Technical Skills

.NET .NET Core IIS Configuration KestrelAPI DevelopmentAPI IntegrationAPI developmentAutomationBackend DevelopmentC#CI/CDCode RefactoringDependency InjectionDevOpsDocumentation

Repositories Contributed To

2 repos

Overview of all repositories you've contributed to across your timeline

umbraco/Umbraco-CMS

Oct 2024 May 2026
7 Months active

Languages Used

XMLC#JavaScriptMarkdownJSONTypeScriptYAMLcshtml

Technical Skills

build configurationerror handlingsoftware maintenance .NETAPI DevelopmentBackend Development

umbraco/UmbracoDocs

Jan 2025 Jun 2026
2 Months active

Languages Used

MarkdownC#YAML

Technical Skills

DocumentationUmbraco CMScontent managementdocumentationtemplate design