What the Spotify FOSS Fund Means to the Maintainers of Jdbi, AssertJ, and Testcontainers
Late last year, Spotify announced the recipients of the 2023 Spotify FOSS Fund. As with previous years, the fund is intended to provide direct monetary support to independent open source projects whose work often goes unseen. We reached out to the maintainers of three of those projects — Jdbi, AssertJ, and Testcontainers — to ask how the funding helps, what challenges they face, and what the broader open source community can do to support projects like theirs.
Henning Schmiedehausen — Jdbi
Henning (@hgschmie) is a chief architect at AppFolio and a maintainer of Jdbi, living in Los Altos, California.
The project's purpose
Jdbi is a utility library for Java that aims to let users get their work done with minimal friction. The project was born out of frustration with the limitations of the API it builds upon, and it continues to focus on supporting users' real-world needs.
How the funds will be used
As a small team of distributed committers, all of whom are employed elsewhere, Jdbi's maintainers plan to use the money for in-person meetups, CI credits, and software licenses. None of the developers are deriving income from the project, so the funds go directly to operational needs.
On the broader impact of FOSS funds
Schmiedehausen notes that while FOSS funds can benefit new projects by accelerating growth, they matter most for mature software that is no longer part of the "hype cycle." Projects that have been around for years — Jdbi has existed since 2005 — are often maintained by a small group of unpaid volunteers. For these "gold standard" libraries, FOSS funds may be the only thing keeping development alive, especially when contributors are no longer working on the project as part of their day jobs.
On contributions and community support
Any amount of money helps, says Schmiedehausen, pointing out the value of small "buy me a coffee" style donations. But time, resources, and code are the three key ingredients for a healthy project. Community members can contribute by fixing bugs, writing documentation, or reviewing open issues. Companies can help by funding projects (as the FOSS Fund does), allowing employees time to contribute during work hours, and decoupling their support from any expectation of control or takeover.
Joel Costigliola — AssertJ
Joel (@joel-costigliola) is the creator of AssertJ, living and working in Auckland.
The project's purpose
AssertJ provides a rich, easy-to-use assertion library for Java. Its goals also include listening to community feedback and making it pleasant for new contributors to get involved.
How the funds will be used
The maintainers are not accustomed to receiving funding, and their most pressing issue is a simple lack of time. The money could be used to buy compensated time away from their respective jobs to focus on AssertJ, or to organize a hackathon.
On the broader impact of FOSS funds
Costigliola sees FOSS funds as valuable for projects that need to pay for infrastructure like servers and hosting, or that want to offer free training. Exposure from the fund is also welcome, even though recognition was never the primary motivation for the project — the goal was always to be helpful.
On community support
Beyond financial support, contributions of all kinds make a difference, from documentation improvements to bug fixes. Maintainers also benefit from specialized expertise they lack, such as web design. As Costigliola puts it, "we suck at CSS stuff," and access to a designer would go a long way.
Sergei Egorov — Testcontainers
Sergei (@bsideup) is co-founder of AtomicJar and Testcontainers, living and working in NYC. Testcontainers was also a recipient of last year's Spotify FOSS Fund.
The project's evolution
Testcontainers is expanding well beyond Java. In October 2023 alone, the project added libraries for Elixir and C. These additions reflect a vision of Testingcontainers as more than a Java-specific tool — it aims to unite developers who want full control over their testing environments. The free Testcontainers Desktop application is part of that ecosystem, lowering the barrier to entry for newcomers.
How this year's funds will be used
The maintainers have been planning a Testcontainers OSS Summit where maintainers of different implementations can meet in person and align on a joint roadmap. The funding from Spotify will make this event more inclusive, allowing the organizers to invite more non-core members.
On the value of recognition over revenue
Egorov believes that no open source project starts out aiming to make money — and probably shouldn't. Instead, the highest-value outcome of a FOSS fund is recognition and endorsement. He credits Spotify's long history of public support for helping Testcontainers attract more contributors and grow faster. If more large companies take a similar approach, it could create a new model for open source sustainability that doesn't rely on professional services, SaaS wrappers, or forced relicensing. He draws a parallel: exceptional engineers rarely want to become businesspeople, and forcing them to focus on monetization could slow the entire industry's progress.
On new ideas for company support
Egorov suggests that larger users of open source projects could form advisory groups. A dedicated developer (or team) from a major corporation could act as a representative, sharing usage patterns and challenges — potentially under an NDA — to give maintainers realistic feedback. This would be a bi-directional relationship where big users help shape the roadmap, with just an hour a month making a substantial difference.
