A small tool that detects licensing information for a given Node.js module


Licenses.. This is the most painful part about Open Source. There are so many different licenses and they all have different restrictions. In order to know the license footprint of your project you need to know how your modules are licensed. You might be interested in your license footprint because:

  • Some licenses might restrict you from selling your code or using it for commercial applications.
  • There are unlicensed modules released in to npm on a daily basis. Just because they are added in the npm registry it doesn't mean that they are Open Source and just free to use.
  • The code could be proprietary licensed.
  • .. and the list goes on and on.

But the biggest problem is figuring out which license a module is actually using. There are a lot of ways of saying that your code is licensed under MIT. There are people who rather say licensed under MIT than just stating MIT. So the way we write which license we use differ but also the location of our licenses. It can be in the package.json hiding in various of properties or specified in the of the project or even a dedicated LICENSE file in the repository.

Now that you've taken the time to read about some of these issues above, you know why this module exists. It tries to fulfill one simple task. Get a human readable license from a given node module.

However, this module isn't flawless as it tries to automate a task that usually requires the interference and intelligence of a human. If you have module that is incorrectly detected or not detected at all but does have licensing information publicly available please create an issue about and we'll see if it can get resolved.

The module is released through npm and can therefor be installed using:

npm install --save licenses

There is CLI version of this module available as licensing which can be installed locally using:

npm install -g licensing

See for more information.

The module exposes one single interface for retrieving the packages, which is a simple exported function:

'use strict';
var licenses = require('licenses');
licenses('primus', function fetched(errlicense) {
  console.log(license.join(',')); // MIT 

As you can see in the example above, the first argument of the function can be a string with the name of the package you want to resolve. In addition to supplying a string you can also give it the contents of the npm registry's data directly:

licenses({ name: 'primus', readme: '..', ....}, function fetched(errlicense) {

The function allows a second optional argument which allows you to configure license function. The following options are supported:

  • githulk A custom or pre-authorized githulk instance. The license lookup process makes extensive use of GitHub to retrieve license information that might not be available in the package.json. But the GitHub API is rate limited so if you don't use an authorized GitHulk instance you can only do 60 calls to the API.
  • order The order in which we should attempt to resolve the license. This defaults to [registry, github, content].
  • registry The URL of The npm Registry we should use to retrieve package data.
  • npmjs a custom npm-registry instance.

The options are completely optional and can therefore be safely omitted.

licenses('primus', { registry: '' }, function () {

As you might have noticed from the options we support three different lookup algorithms:

In this algorithm we attempt to search for license information directly in the supplied or retrieved npm data. This is the fastest lookup as it only needs to search and parse the license and licenses fields of the module for license information.

This reads out your github repository information from the package data to get a directly listing of your project. Once the directory is listed it fetches files from the repo where a possible license or license information can be found like README and LICENSE files. All the data that is found will be scanned with the content algorithm.

It searches the readme or supplied content for matches the license files. If it fails to do any matching based on the license files it fallback to a really basic regexp based check.