FCL (Fair Core License) is a Fair Source license designed for developer tools and infrastructure projects that want to share their code while still protecting their business model. It allows users to read, use, modify, and redistribute the project, but “use” excludes purposes that compete with the author’s commercial interests. The text emphasizes that for most users who do not intend to compete with the author’s business, the license offers a relatively high degree of freedom; each software version converts to an open-source license 2 years after release.
FCL’s core value is that it supports releasing core functionality and commercial functionality within the same codebase under the same license. Commercial features can be gated with a license key to prevent unauthorized access. Compared with FSL, it is better suited to projects that include self-hosted commercial features; compared with ELv2, its eventual conversion to an open-source license reduces the risk that users will lose long-term access to commercial features if the licensor stops providing service. Compared with Open Core, FCL does not require commercial features to be split into a separate ee/ directory or distributed under a closed-source license, so migration costs are lower.
FCL is not a traditional immediately open-source license, but rather a Fair Source model with a non-compete restriction. It supports conversion to Apache 2.0 or MIT after 2 years. The license was drafted by Heather Meeker and contributed by Keygen, with references to Sentry’s FSL and Elastic’s ELv2. Current materials are mainly FAQ-based and explain the concepts and differences clearly, but they lack deeper implementation examples, project governance guidance, and legal adaptation guides.
The main text does not provide pricing information for FCL itself. Its advantages are that it balances commercial sustainability with eventual open source, making it suitable for commercial self-hosted and on-premise projects, as well as teams moving from closed source to Fair Source. Its main drawbacks are that the non-compete clause may leave room for interpretation, making it unsuitable for projects seeking full open source in the OSI sense; it also only supports Apache 2.0 and MIT as conversion licenses.
FCL is suitable for developer tool, infrastructure, and enterprise software vendors, especially teams that monetize self-hosted commercial features while still wanting to publish the full codebase. Access from China is not mentioned in the source text, so it is considered unknown. Alternatives include FSL, ELv2, Open Core, traditional closed-source licensing, or directly adopting MIT/Apache 2.0.
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