If the binder had a constitution, it would be a single page drafted in early 1998. The Open Source Definition began life as the Debian Free Software Guidelines, written by Bruce Perens for the Debian project, and it was lifted almost unchanged when a small group around Eric Raymond needed a public standard for the new phrase open source. Ten numbered criteria, each one short enough to read aloud, each one aimed at a specific way a license could quietly fail.

More than a quarter of a century later, every argument about whether a license counts as open source is still an argument about those ten lines. This sheet walks them in order, not as history but as a working tool: the definition is the ruler the binder lays against every new text that arrives.

Free redistribution

The first criterion says the license may not restrict anyone from selling or giving away the software, alone or inside a larger collection, and may not require a royalty for doing so. It was written against the habit of vendors who let you read a CD but invoiced you for sharing it. The moment a license charges per copy, it stops being open source, which is why the old contribute-or-pay experiments of the early 2000s always sat outside the gate.

Source code you can actually get

Criterion two demands that the program include source code, or that source be obtainable for no more than a reasonable reproduction cost, and that deliberate obfuscation is forbidden. The target here was the halfway gesture: a vendor showing a listing on paper, or shipping commented-out fragments, while keeping the real build inputs private. The definition insists the source be the form in which a programmer would actually modify the program.

The clause sounds obvious and it was not. In 1998 the industry was full of source-access programs that showed code without conveying it: read-only listings, encrypted tarballs, printed manuals. The criterion is what separates the shared source era's look-but-do-not-touch texts from the real thing, and it is why a repository that ships minified or generated code without its inputs fails the test even when the bytes are technically readable.

Derived works

Criteria three and four are the pair that govern modification. A conforming license must allow derived works and must let them circulate under the same terms as the original. But criterion four carries a famous compromise: a license may require that modifications ship as separate patch files at build time, and it may require derived works to carry a different name or version number. That clause was negotiated to accommodate software whose authors wanted to protect the integrity of the original release.

No discrimination

Criteria five and six are the two sentences that do the most work today. No discrimination against persons or groups, and no discrimination against fields of endeavor. A license may not forbid use in business, or in genetic research, or by a competitor of the author. This is the clause that pushes the entire source-available family off the open source shelf: the moment a license says you may not offer the software as a competing service, criterion six is breached, whatever else the text permits.

It is also the clause that generates the most argument, because it forces the definition to choose between protecting users and protecting authors' income. The definition chose users, once and for all, in 1998, and every later attempt to attach a commercial carve-out has had to live with being filed somewhere other than the open shelf.

The closing four

Criterion seven says the rights attach to everyone who receives the program, without needing an additional agreement; it prevents a license from being routed through a chain of private contracts. Criterion eight adds that the rights must not depend on the software being part of a particular distribution, which keeps a vendor from releasing code inside a bundle while reserving it elsewhere.

Criteria nine and ten are housekeeping. A license must not restrict other software distributed alongside the covered program, which protects collections and package managers. And the license must be technology-neutral, written so it does not presume a specific interface, medium, or style of distribution. These closing lines keep the definition usable as the channels of delivery change.

Why ten lines still sort the shelf

The definition also survives because it is small enough to be applied by hand. A reader does not need a committee to check a license against ten criteria; they need the text and a pencil. That accessibility is what kept it the standard while longer, more sophisticated frameworks came and went.

What makes the definition durable is that it was written as a fence, not a manifesto. Each criterion closes a loophole someone had already used or was about to. When a new license arrives, the reader's job is mechanical: walk the ten points, mark where the text breaks one, and file it accordingly. The binder respects that mechanics. It is how the collaborative source texts of 2003, the shared source licenses of 2001, and the delayed-release licenses of the 2010s all end up on neighboring but distinct shelves, and why none of them pretends to be what it is not.

What the text grants

Ten criteria that turn open source from a mood into a checklist: free redistribution, real source, derivatives, no discrimination.

What a reader should check

Where a new license breaks a criterion, usually number one on royalties or number six on fields of use.

The limit of this reading

The definition sorts licenses, but it does not measure the health of the community standing behind them.