Justinas Rumševičius
Senior Software Engineer at Ledger
Saint-Genis-Pouilly, Auvergne-Rhône-Alpes, France
Summary
👤
Senior🎓
Top SchoolJustinas Rumševičius is a Senior Software Engineer with a decade of hands-on experience building backend systems, web tools, and developer utilities across research and enterprise contexts. Based in Saint-Genis-Pouilly, he moved from CERN—where he maintained and refactored critical CMS validation and Monte Carlo tooling and automated workflows—to Ledger, contributing to enterprise-grade self-custody crypto products. He combines strong Python and backend skills with practical system administration, test-driven feature delivery, and a knack for improving developer workflows (notably contributing to CMS offline software and MC production tooling). Always learning and determined to get things done, he balances deep technical maintenance with feature delivery and user-focused automation. An eye for refactoring and integrations makes him particularly effective at turning complex validation and build processes into robust, reusable tools.
10 years of coding experience
10 years of employment as a software developer
Master’s Degree Informatics, Master’s Degree Informatics at Vilniaus universitetas / Vilnius University
English, Lithuanian, French
Stackoverflow
66reputation
1kreached
4answers
1question
Github Skills (26)
c-language10
python10
cer10
cprogramming-language10
configuration-management9
performance-optimization9
optmization9
optimisation9
optimization9
rest-api9
cli8
command-line-interface8
command-line8
build-system8
debug8
Programming languages (7)
Github contributions (5)
cms-sw/cmssw
Aug 2020 - Jul 2021
CMS Offline Software
Role in this project:
Back-end Developer
Back-end DeveloperContributions:4 reviews, 22 commits, 22 PRs in 11 months
Contributions summary:Justinas primarily contributed to the backend software development for the CMS Offline Software project. Their work involved modifying existing code, specifically refactoring and optimizing modules within the `Configuration/PyReleaseValidation` and `GeneratorInterface/LHEInterface` directories, and updating DBS configuration. A significant portion of their work involved making changes to matrix configuration and the associated injection process, and enhancing the handling of External LHE producers. These changes reflect a focus on improving build processes and data handling.
cmscernweb-appc-plus-plusbackbonejs
cms-sw/genproductions
Feb 2019 - Mar 2019
Generator fragments for MC production
Role in this project:Backend Developer
Backend DeveloperContributions:8 commits, 1 PR, 1 comment in 4 days
Contributions summary:Justinas primarily contributed to the development of a Python-based utility for checking request fragments within the context of a MC production environment. Their commits introduced and refined functionalities such as handling cookie authentication, incorporating a development mode, and migrating to a public API. The contributions focus on enhancing the tool's usability, integrating with external services, and improving error handling. The user also refactored the code by updating paths to external libraries.
productionfragments
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