Why we say "not open source"

Version 1.2 · August 2026

Every ISL license carries the same sentence near the top: "This is not an open-source license." We volunteer that, prominently, rather than letting the question slide. This page documents the reasoning.

"Open source" is a defined term

"Open source" is not a general description of visible source code. It is a term of art with a formal definition, the Open Source Definition (OSD), maintained by the Open Source Initiative since 1998. Two of its ten criteria decide the matter here. Criterion 5 forbids discrimination against persons or groups. Criterion 6 forbids discrimination against fields of endeavor; the OSD's own example is that a license may not forbid use in a business or in genetic research.

Sections 4 and 5 of every ISL license do precisely what criterion 6 forbids: they deny the software to gambling platforms, interest-based lenders, pornography, and the other prohibited industries. So no ISL license can ever be open source, no matter how generous ISL-P is otherwise. The Hippocratic License and the Do No Harm License are classified as non-free by both the OSI and the FSF for exactly the same reason.

The restrictions are the point

The disclaimer says "by design" because this incompatibility is not a defect we are apologizing for. We chose the restrictions over the label, knowingly. The restrictions are the product.

Honesty is the Islamic position

Truthful representation of what one offers is an Islamic obligation. A license family built on Islamic ethics that claimed a label it does not meet would wound its own credibility at the foundation. Projects that stretched the term "open source" over restricted licenses, as happened around the Commons Clause, MongoDB's SSPL, and HashiCorp's move to the Business Source License, were publicly corrected and paid for it in trust. We preempt the single most predictable objection by raising it ourselves, first.

What it means for you practically

Much of the software world treats "open source" as a machine-checkable gate. Corporate legal departments auto-approve OSI-approved licenses; ISL-licensed software will need an actual review. Linux distributions such as Debian and Fedora ship only OSD-free software, so ISL-licensed projects will not enter their archives. Registry and repository tooling classifies by license and will show these as non-standard. None of this is unfair; it is what the restrictions cost, and you should know it before choosing them.

The honest category

"Source-available" is the established term for licenses that let you read the code while limiting the rights, and it covers respectable company: the Business Source License (MariaDB, HashiCorp), the Elastic License 2.0, the SSPL. That is the category thirteen of the fourteen ISL licenses belong to, and the one we claim for them. ISL-EULA is the exception and does not claim it: it licenses no source code, and its own text says it "is not an open-source or source-available license".

"Not open source" does not mean closed to contributors

The two are routinely confused, so it is worth separating them. Open source is a statement about what a user may do with the software; a contribution model is a statement about what an author may send back. Nothing about restricting the first forecloses the second.

Most of the family says so outright: ISL-P, ISL-C, ISL-LC, ISL-NETC and ISL-NC each carry a Section 6 headed Contributions, which sets the terms a submitted patch arrives on. A license family that expected no contributors would not need one.

Even ISL-R, the most restrictive software variant and the only one without such a section, was drafted with the door left open. Its Section 2 prohibits modification and derivative works "without prior written consent from the Licensor" — and consent is exactly what a contributor agreement is. The family publishes one for this purpose, ISL-CLA, currently a draft. With it signed, an ISL-R project can accept a patch without relicensing, without weakening Sections 4 and 5, and without any claim to a label it does not meet. The consent covers preparing and submitting a contribution and nothing else; it is not permission to publish a modified build.

For the variants that already have their Section 6, the agreement is what that section itself points to: those defaults apply "unless a Contributor and the Licensor have executed a separate written agreement stating otherwise." The agreement is that separate writing, and it exists because the default grant is only as broad as the license it arrives under — a contribution to an ISL-C project comes in under ISL-C and must stay there, which is the right default and an obstacle to a licensor who also sells the work.

So the honest description of an ISL project is ethically restricted in what it may be used for, and open to whoever wants to help build it. Those are compatible, and the second is not a concession.

What the disclaimer does not mean

It does not mean the software costs money. It does not mean you cannot use, modify, or redistribute it; ISL-P and ISL-C permit all of that. It does not mean the licenses are legally weaker. Only the label is at stake, and we would rather lose the label than the truth.