The last thing you need to do before your package is a proper R
package is to choose a license for your software and specify the
license within the
Software licenses are about two things: copyright, and protecting yourself from being held liable if your software screws something up somewhere down the line.
I know next to nothing about copyright law outside the United States, but in the US, copyright is automatic (you don’t need to write “© 2014 A. Pendantic Person, All Rights Reserved” all over the place, or even once), and it gives you exclusive rights to copy your code. So if you don’t choose a license for your software, no one else can use it!
There are lots of different software licenses to choose from. That’s part of why this is such a painful topic. (That they are almost all really boring to read is another part of the pain. The WTFPL is one of the few that is not boring.)
Personally, I choose between the MIT license and the GNU General Public License (GPL). The MIT license is among the more permissive. The GPL is “viral” in that it extends to derivative works: software that incorporates code that was licensed under the GPL must also be licensed under the GPL. So I use the GPL if I have to (that is, if I’ve incorporated others’ GPL code), and I use the MIT license otherwise.
Don’t use a Creative Commons license for software
An important thing to remember: don’t use a Creative Commons (CC) license for software. Creative Commons licenses (like CC-BY) are great, but they’re for things like articles, books, and videos, but not software. As they say in their FAQ:
We recommend against using Creative Commons licenses for software.
Use CC licenses for your lecture notes, slides, and articles, but not for your software.
What about CC0?
CC0 (public domain) seems appropriate for software: you’re just saying that anyone can do anything with the code.
But in some states (e.g., Maryland, I think), software is treated as a “good” (like a car), and so if your code causes something terrible to happen, you could be sued for damages. Using a lenient license, like the MIT license, eliminates that potential problem through the “no warranty” clause.
Indicating your choice in your package
So, pick a license, any license. And then indicate your choice in the
DESCRIPTION file for your R package.
GNU General Public License (GPLv3)
To use the GPLv3 with your R package, include the following line in
If you’re not incorporating code that is licensed under the GPL, I recommend going with the MIT license.
Unfortunately, and for reasons that I don’t understand, the R Core
considers the MIT license to be not a proper license but rather a
template for a license. And so if you want to use the MIT license,
you must include a
LICENSE file in your package that includes just
like this (example here):
YEAR: 2014 COPYRIGHT HOLDER: Karl W Broman
See the license template at http://www.r-project.org/Licenses/MIT.
Then, in your
DESCRIPTION file, include the following line.
License: MIT + file LICENSE
The all caps
LICENSE in that line is the name of the file (within
your package) with the text about year and copyright holder. You can
also call the file
LICENCE if you want. In this case, the relevant
line in your
DESCRIPTION file should be the following.
License: MIT + file LICENCE
(I’d thought that you could use a different name for the file, for
License.txt, but the
Writing R Extensions manual
seems pretty explicit that the file should be either
With this, our package looks like this, and it is now a proper R package.
Pick a license for your software, make the appropriate change to your
DESCRIPTION file, and if necessary add a
Then go to the page about checking an R package.