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25.0.1 • Public • Published

NPM License Checker

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As of v17.0.0 the failOn and onlyAllow arguments take semicolons as delimeters instead of commas. Some license names contain commas and it messed with the parsing

Ever needed to see all the license info for a module and its dependencies?

It's this easy:

npm install -g license-checker
mkdir foo
cd foo
npm install yui-lint

You should see something like this:

├─ cli@0.4.3
│  ├─ repository:
│  └─ licenses: MIT
├─ glob@3.1.14
│  ├─ repository:
│  └─ licenses: UNKNOWN
├─ graceful-fs@1.1.14
│  ├─ repository:
│  └─ licenses: UNKNOWN
├─ inherits@1.0.0
│  ├─ repository:
│  └─ licenses: UNKNOWN
├─ jshint@0.9.1
│  └─ licenses: MIT
├─ lru-cache@1.0.6
│  ├─ repository:
│  └─ licenses: MIT
├─ lru-cache@2.0.4
│  ├─ repository:
│  └─ licenses: MIT
├─ minimatch@0.0.5
│  ├─ repository:
│  └─ licenses: MIT
├─ minimatch@0.2.9
│  ├─ repository:
│  └─ licenses: MIT
├─ sigmund@1.0.0
│  ├─ repository:
│  └─ licenses: UNKNOWN
└─ yui-lint@0.1.1
   ├─ licenses: BSD
      └─ repository:

An asterisk next to a license name means that it was deduced from an other file than package.json (README, LICENSE, COPYING, ...) You could see something like this:

└─ debug@2.0.0
   ├─ repository:
   └─ licenses: MIT*


  • --production only show production dependencies.
  • --development only show development dependencies.
  • --start [path of the initial json to look for]
  • --unknown report guessed licenses as unknown licenses.
  • --onlyunknown only list packages with unknown or guessed licenses.
  • --json output in json format.
  • --csv output in csv format.
  • --csvComponentPrefix prefix column for component in csv format.
  • --out [filepath] write the data to a specific file.
  • --customPath to add a custom Format file in JSON
  • --exclude [list] exclude modules which licenses are in the comma-separated list from the output
  • --relativeLicensePath output the location of the license files as relative paths
  • --summary output a summary of the license usage',
  • --failOn [list] fail (exit with code 1) on the first occurrence of the licenses of the semicolon-separated list
  • --onlyAllow [list] fail (exit with code 1) on the first occurrence of the licenses not in the semicolon-seperated list
  • --packages [list] restrict output to the packages (package@version) in the semicolon-seperated list
  • --excludePackages [list] restrict output to the packages (package@version) not in the semicolon-seperated list
  • --excludePrivatePackages restrict output to not include any package marked as private
  • --direct look for direct dependencies only


A list of licenses is the simplest way to describe what you want to exclude.

You can use valid SPDX identifiers. You can use valid SPDX expressions like MIT OR X11. You can use non-valid SPDX identifiers, like Public Domain, since npm does support some license strings that are not SPDX identifiers.


license-checker --json > /path/to/licenses.json
license-checker --csv --out /path/to/licenses.csv
license-checker --unknown
license-checker --customPath customFormatExample.json
license-checker --exclude 'MIT, MIT OR X11, BSD, ISC'
license-checker --packages 'react@16.3.0;react-dom@16.3.0;lodash@4.3.1'
license-checker --excludePackages 'internal-1;internal-2'
license-checker --onlyunknown

Custom format

The --customPath option can be used with CSV to specify the columns. Note that the first column, module_name, will always be used.

When used with JSON format, it will add the specified items to the usual ones.

The available items are the following:

  • name
  • version
  • description
  • repository
  • publisher
  • email
  • url
  • licenses
  • licenseFile
  • licenseText
  • licenseModified

You can also give default values for each item. See an example in customFormatExample.json.


var checker = require('license-checker');
    start: '/path/to/start/looking'
}, function(err, packages) {
    if (err) {
        //Handle error
    } else {
        //The sorted package data
        //as an Object


license-checker uses debug for internal logging. There’s two internal markers:

  • license-checker:error for errors
  • license-checker:log for non-errors

Set the DEBUG environment variable to one of these to see debug output:

export DEBUG=license-checker*; license-checker
scanning ./yui-lint
├─ cli@0.4.3
│  ├─ repository:
│  └─ licenses: MIT
# ... 

How Licenses are Found

We walk through the node_modules directory with the read-installed module. Once we gathered a list of modules we walk through them and look at all of their package.json's, We try to identify the license with the spdx module to see if it has a valid SPDX license attached. If that fails, we then look into the module for the following files: LICENSE, LICENCE, COPYING, & README.

If one of the those files are found (in that order) we will attempt to parse the license data from it with a list of known license texts. This will be shown with the * next to the name of the license to show that we "guessed" at it.



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  • davglass