Felix worked on improving the stability of API documentation in the mittwald/developer-portal repository by addressing issues related to DNS TTL changes. He implemented adjustments to DNS TTL settings, ensuring that updates to the documentation would not introduce breaking changes for users and allowing for smoother transitions during API updates. His approach included updating API change notes in Markdown to clearly communicate the new non-breaking TTL behavior, which helped reduce user confusion and support requests. Throughout the process, Felix maintained clear, signed-off commits using version control best practices, demonstrating attention to maintainability and traceability in technical writing and documentation.