Joost Jager
Software Developer at Block
Arnhem-Nijmegen Region Netherlands
Summary
🤩
Rockstar🎓
Top SchoolJoost Jager is a pragmatic software developer with 10+ years building secure, production-grade backend systems and a deep focus on Bitcoin and the Lightning Network. He has been a top open-source contributor to prominent projects like lnd and helped implement core features such as Lightning Loop and hardened onion routing error handling to improve robustness and concurrent packet processing. His career spans startups and large engineering teams—shaping wallets, custody solutions, and payment infrastructure at Bottlepay, NYDIG, Lightning Labs and now Block—while also leading cross-disciplinary product efforts in hardware and UX. Trained in AI and cognitive science, he applies algorithmic thinking to practical problems from route optimization to ML-driven interactive experiences. Colleagues describe him as a team player who prefers shipping secure, well-architected solutions and who quietly brings real-world leadership experience, from commanding a sailing fleet to steering complex technical projects.
10 years of coding experience
25 years of employment as a software developer
Master of Science Technical Informatics with a major in AI / Cognitive Science, Master of Science Technical Informatics with a major in AI / Cognitive Science at Radboud University
Dutch, English
Github Skills (20)
crypto-wallet10
transaction10
wallet10
lightning-network10
bitcoin-wallet10
bitcoin10
bitcoins10
transactionscope10
go10
cryptography10
blockchain10
transaction-manager10
ethereum-wallet10
micro-c9
microcoin9
Programming languages (13)
Github contributions (5)
lightninglabs/loop
Mar 2019 - Aug 2020
Lightning Loop: A Non-Custodial Off/On Chain Bridge
Role in this project:
Back-end Developer
Back-end DeveloperContributions:3 releases, 82 reviews, 135 commits in 1 year 6 months
Contributions summary:Joost implemented the initial version of Lightning Loop, a non-custodial off/on chain bridge. Their work primarily focused on creating the core client-side logic for uncharge swaps. This included implementing the client's interaction with the loop server, handling swap initiation, and managing the on-chain HTLC process. The user's commits demonstrate a focus on building the back-end components of the loop protocol.
bridgeblockchainlightningon-chainloop
lightningnetwork/lightning-onion
Jun 2019 - Sep 2022
Onion Routed Micropayments for the Lightning Network
Role in this project:Back-end Developer
Back-end DeveloperContributions:24 reviews, 7 commits, 6 PRs in 3 years 3 months
Contributions summary:Joost made several contributions focused on improving the error handling and security within the Lightning Network's onion routing implementation. They introduced changes to the error decryption process, allowing for more flexible error handling with potential future extensions. The user also addressed code related to the maximum payload size, ensuring that the packet size validation is correct, including allowing concurrent onion packet processing. These changes enhance the robustness and security of the onion routing mechanism.
cryptographyonion-architecturelightningblockchainonion
Find and Hire Top DevelopersWe’ve analyzed the programming source code of over 60 million software developers on GitHub and scored them by 50,000 skills. Sign-up on Prog,AI to search for software developers.