Tech companies take notice: The copyrightability of software application programming interfaces — or APIs — is on shaky constitutional ground.

Google LLC v. Oracle America Inc., the most closely watched copyright case in recent memory, called on the U.S. Supreme Court to determine whether software APIs are copyrightable and, if so, whether Google’s admitted copying of parts of the Java API constituted fair use.

In its 6-2 decision on April 5, the court neatly sidestepped the question of copyrightability, finding that Google’s actions constituted fair use regardless of whether the Java API was copyrightable.

However, the skepticism in the court’s analysis is hard to miss and should give pause to future parties seeking to enforce copyrights on software APIs.

In finding fair use, the court looked to the four factors set out in Section 107 of the Copyright Act, which seek to balance copyright holders’ interests with society’s interest in the reproduction and transformation of scientific and artistic content. While the court’s analysis purports to apply narrowly to the facts of this case, it does suggest broader applicability to software APIs in general.

Nature of copyrighted work

Here, the “work” in question was the “declaring code,” which provides the “interface” element of an API. The declaring code determines the organizational hierarchy of methods and tells calling code how to invoke them.

In contrast, “implementing code” provides a method’s internal functionality, and a “method call” is a particular instance of utilizing or “calling” a method.

Google copied the declaring code from the Java API but wrote its own implementing code tailored to the Android smartphone platform.

Likening declaring code to a filing system, the court found that “declaring code is, if copyrightable at all, further than are most computer programs (such as implementing code) from the core of copyright.”

With such skeptical language, the court appears to have walked right up to the line of finding declaring code to be uncopyrightable, but it ultimately declined to step across.

Purpose, character of use

Google copied the Java API in order to make the Android platform more readily accessible to Java programmers. Because they were already familiar with Java, programmers could write applications for Android without needing to learn an entirely new API.

Copying the Java API to Android thus facilitated the creation of new products that were not available on non-mobile platforms. Bringing that ease of creation to a smartphone platform, the court found, constituted a “transformative” use that was not outweighed by the commercial nature of Google’s endeavor.

The skepticism in the court’s analysis is hard to miss and should give pause to future parties seeking to enforce copyrights on software APIs.

That kind of transformation does not occur when a company copies a competitor’s API on the same platform. Therefore, if software APIs are copyrightable, then this factor could limit the scope of permissible fair use considerably.

Amount, substantiality of portion used

The declaring code that Google copied was a very small portion of the Java programming language: about 11,500 lines of code, constituting 0.4 percent of the total when implementing code is included.

In addition, in view of the court’s analysis of the “nature” of declaring code, the copied lines of code were insubstantial in comparison to the implementing code. Google only copied what was needed to achieve the “transformative” purpose of attracting Java developers to the Android platform.

Those distinctions are not unique to the Java API. Given that declaring code is a small fraction of the total code in any sizeable project, we should expect this factor to weigh in favor of fair use in nearly any case.

Market effects

Here, the court highlighted trial evidence suggesting that Sun (Oracle’s predecessor) was not competing with Google in the smartphone space.

“Google’s Android platform was part of a distinct (and more advanced) market than Java software,” the court found.

In fact, bringing the Java API to Android might have benefitted Sun by encouraging even more developers to learn the Java programming language.

Meanwhile, foreclosing Google from porting the Java API to Android would amount to “a lock limiting the future creativity of new programs” by programmers who had invested their time in learning the Java API.

That latter argument reflects a reality of the software industry as a whole: Denying a programmer access to the APIs they already know will limit their creative abilities, at least until they are able to learn a new API that is available on the target platform.

Prior to the court’s decision, many in the software industry were concerned that a finding against copyrightability would discourage companies from developing new APIs that could then be copied by competitors. Others feared that a finding for copyrightability would be the death knell for open source projects that replicate commercial APIs.

By avoiding the copyrightability question altogether and deciding the case narrowly on the specific facts of the case, the court seems to have averted either outcome.

However, the court’s analysis reveals healthy skepticism toward copyrightability of software APIs generally, and its application of the fair use factors suggests that future claimants face a potentially fruitless uphill battle.

Rackham H. Karlsson is an associate at intellectual property firm Lando & Anastasi in Boston. He can be contacted at [email protected].