Zef Hemel
Chief Technology Officer at Fixly.pl
Poznan, Greater Poland Voivodeship
Summary
🤩
Rockstar🎓
Top SchoolZef Hemel is a seasoned technology leader and CTO with 18 years of experience building and scaling engineering organizations across Europe and globally. He has a proven track record of stepping into diverse contexts—startups, scaleups and large platforms—and rapidly orienting teams from a handful of engineers to organizations of ~100, while combining hands-on product development with strategic leadership. Technically fluent across full-stack systems, distributed architectures and AI platforms, he has shipped client-facing UI work (notably contributions to the Ace editor and several developer tools) as well as core backend features and integrations. His leadership spans serverless, cloud-native and traditional stacks (Go, Kotlin, TypeScript, Python, Java) and emphasizes pragmatic delivery, mentoring managers and aligning product and engineering outcomes. A PhD-trained computer scientist and occasional writer/editor on tech leadership, he brings both research rigor and a knack for spotting repeatable patterns and traps in engineering organizations. Based in Poznań, he is known for quickly turning chaotic situations into stable roadmaps and for contributing subtle UX improvements in open source projects that disproportionately improve developer experience.
18 years of coding experience
14 years of employment as a software developer
M.Sc. Networks & Distributed Systems, M.Sc. Networks & Distributed Systems at Trinity College DublinB.Sc. English, B.Sc. English at University of GroningenPhD Computer Science, PhD Computer Science at Delft University of Technology
Polish, Dutch, English
Stackoverflow
6,607reputation
255kreached
12answers
7questions
rest
top-5%
versioning
top-5%
Github Skills (44)
markdown10
editors10
javascript10
text-editor10
testing10
typescript10
websocket10
ui-design10
editor10
uid10
markdown-it10
front-end-development10
typescript-types10
html10
code-editor10
Programming languages (14)
Github contributions (5)
coresmart/persistencejs
Jun 2010 - Aug 2015
persistence.js is an asynchronous Javascript database mapper library. You can use it in the browser, as well on the server (and you can share data models between them).
Role in this project:
Back-end Developer
Back-end DeveloperContributions:206 commits, 4 PRs, 4 pushes in 5 years 3 months
Contributions summary:Zef primarily contributed to the core functionality of the `persistence.js` library, focusing on features related to database mapping and query collection operations. They implemented the ability to assign `LocalQueryCollection` objects to entity properties and added methods like `destroyAll` and `count` to query collections. Their work also involved refactoring code for multi-connection systems and addressing bug fixes related to the library's API and database interaction.
asynchronousbrowserjavascriptdata-modelsasynchronous-javascript
silverbulletmd/silverbullet
Feb 2022 - Jan 2023
The knowledge tinkerer's notebook
Role in this project:Full-stack Developer
Full-stack DeveloperContributions:2 releases, 105 reviews, 738 commits in 11 months
Contributions summary:Zef contributed extensively to the development of SilverBullet, a note-taking application focused on knowledge management and end-user programming. The commits demonstrate a focus on implementing new features related to markdown editing, text manipulation, and command support, suggesting a focus on UI/UX. The user worked on features, indicating a strong understanding of both front-end and backend aspects. The contributions indicate a strong understanding of both UI and core functionality.
reactnote-takingpersonal-knowledge-managementmarkdownknowledge-management
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