package.json (5) - Linux Man Pages

package.json: Specifics of npm's package.json handling


package.json - Specifics of npm's package.json handling


This document is all you need to know about what's required in your package.json file. It must be actual JSON, not just a JavaScript object literal.

A lot of the behavior described in this document is affected by the config settings described in npm help 7 npm-config.


The most important things in your package.json are the name and version fields. Those are actually required, and your package won't install without them. The name and version together form an identifier that is assumed to be completely unique. Changes to the package should come along with changes to the version.

The name is what your thing is called.

Some rules:

The name must be shorter than 214 characters. This includes the scope for scoped packages.
The name can't start with a dot or an underscore.
New packages must not have uppercase letters in the name.
The name ends up being part of a URL, an argument on the command line, and a folder name. Therefore, the name can't contain any non-URL-safe characters.

Some tips:

Don't use the same name as a core Node module.

A name can be optionally prefixed by a scope, e.g. @myorg/mypackage. See npm help 7 npm-scope for more detail.



Version must be parseable by node-semver, which is bundled with npm as a dependency. (npm install semver to use it yourself.)

More on version numbers and ranges at npm help 7 semver.


Put a description in it. It's a string. This helps people discover your package, as it's listed in npm search.


Put keywords in it. It's an array of strings. This helps people discover your package as it's listed in npm search.


The url to the project homepage.

NOTE: This is not the same as "url". If you put a "url" field, then the registry will think it's a redirection to your package that has been published somewhere else, and spit at you.

Literally. Spit. I'm so not kidding.


The url to your project's issue tracker and / or the email address to which issues should be reported. These are helpful for people who encounter issues with your package.

It should look like this:

{ "url" : ""
, "email" : "project [at]"

You can specify either one or both values. If you want to provide only a url, you can specify the value for "bugs" as a simple string instead of an object.

If a url is provided, it will be used by the npm bugs command.


You should specify a license for your package so that people know how they are permitted to use it, and any restrictions you're placing on it.

If you're using a common license such as BSD-2-Clause or MIT, add a current SPDX license identifier for the license you're using, like this:

{ "license" : "BSD-3-Clause" }

You can check the full list of SPDX license IDs Ideally you should pick one that is OSI approved.

If your package is licensed under multiple common licenses, use an SPDX license expression syntax version 2.0 string, like this:

{ "license" : "(ISC OR GPL-3.0)" }

If you are using a license that hasn't been assigned an SPDX identifier, or if you are using a custom license, use the following valid SPDX expression:

{ "license" : "SEE LICENSE IN <filename>" }

Then include a file named <filename> at the top level of the package.

Some old packages used license objects or a "licenses" property containing an array of license objects:

// Not valid metadata
{ "license" :
  { "type" : "ISC"
  , "url" : ""

// Not valid metadata
{ "licenses" :
    { "type": "MIT"
    , "url": ""
  , { "type": "Apache-2.0"
    , "url": ""

Those styles are now deprecated. Instead, use SPDX expressions, like this:

{ "license": "ISC" }

{ "license": "(MIT OR Apache-2.0)" }

Finally, if you do not wish to grant others the right to use a private or unpublished package under any terms:

{ "license": "UNLICENSED"}

Consider also setting "private": true to prevent accidental publication.

people fields: author, contributors

{ "name" : "Barney Rubble"
, "email" : ""
, "url" : ""


"Barney Rubble <> ("

Both email and url are optional either way.



The "files" field is an array of files to include in your project. If you name a folder in the array, then it will also include the files inside that folder. (Unless they would be ignored by another rule.)

You can also provide a ".npmignore" file in the root of your package or in subdirectories, which will keep files from being included, even if they would be picked up by the files array. The .npmignore file works just like a .gitignore.

Certain files are always included, regardless of settings:

README (and its variants)
CHANGELOG (and its variants)

Conversely, some files are always ignored:








To use this, supply a bin field in your package.json which is a map of command name to local file name. On install, npm will symlink that file into prefix/bin for global installs, or ./node_modules/.bin/ for local installs.

For example, myapp could have this:

{ "bin" : { "myapp" : "./cli.js" } }

So, when you install myapp, it'll create a symlink from the cli.js script to /usr/local/bin/myapp.

If you have a single executable, and its name should be the name of the package, then you can just supply it as a string. For example:

{ "name": "my-program"
, "version": "1.2.5"
, "bin": "./path/to/program" }

would be the same as this:

{ "name": "my-program"
, "version": "1.2.5"
, "bin" : { "my-program" : "./path/to/program" } }




{ "name" : "foo"
, "version" : "1.2.3"
, "description" : "A packaged foo fooer for fooing foos"
, "main" : "foo.js"



{ "name" : "foo"
, "version" : "1.2.3"
, "main" : "foo.js"



{ "name" : "foo"
, "version" : "1.2.3"
, "main" : "foo.js"

will create entries for man foo and man 2 foo


The CommonJS Packages spec details a few ways that you can indicate the structure of your package using a directories object. If you look at npm's package.json, you'll see that it has directories for doc, lib, and man.



Tell people where the bulk of your library is. Nothing special is done with the lib folder in any way, but it's useful meta info.


If you specify a bin directory in directories.bin, all the files in that folder will be added.

Because of the way the bin directive works, specifying both a bin path and setting directories.bin is an error. If you want to specify individual files, use bin, and for all the files in an existing bin directory, use directories.bin.







Specify the place where your code lives. This is helpful for people who want to contribute. If the git repo is on GitHub, then the npm docs command will be able to find you.

Do it like this:

"repository" :
  { "type" : "git"
  , "url" : ""

"repository" :
  { "type" : "svn"
  , "url" : ""


For GitHub, GitHub gist, Bitbucket, or GitLab repositories you can use the same shortcut syntax you use for npm install:

"repository": "npm/npm"

"repository": "gist:11081aaa281"

"repository": "bitbucket:example/repo"

"repository": "gitlab:another/repo"


The "scripts" property is a dictionary containing script commands that are run at various times in the lifecycle of your package. The key is the lifecycle event, and the value is the command to run at that point.

See npm help 7 npm-scripts to find out more about writing package scripts.


A "config" object can be used to set configuration parameters used in package scripts that persist across upgrades. For instance, if a package had the following:
{ "name" : "foo"
, "config" : { "port" : "8080" } }

and then had a "start" command that then referenced the npm_package_config_port environment variable, then the user could override that by doing npm config set foo:port 8001.

See npm help 7 npm-config and npm help 7 npm-scripts for more on package configs.


Dependencies are specified in a simple object that maps a package name to a version range. The version range is a string which has one or more space-separated descriptors. Dependencies can also be identified with a tarball or git URL.

Please do not put test harnesses or transpilers in your dependencies object. See devDependencies, below.

See npm help 7 semver for more details about specifying version ranges.

version Must match version exactly
>version Must be greater than version
>=version etc
~version "Approximately equivalent to version" See npm help 7 semver
^version "Compatible with version" See npm help 7 semver
1.2.x 1.2.0, 1.2.1, etc., but not 1.3.0
http://... See 'URLs as Dependencies' below
* Matches any version
"" (just an empty string) Same as *
version1 - version2 Same as >=version1 <=version2.
git... See 'Git URLs as Dependencies' below
user/repo See 'GitHub URLs' below
tag A specific version tagged and published as tag See npm help npm-tag
path/path/path See Local Paths below

For example, these are all valid:

{ "dependencies" :
  { "foo" : "1.0.0 - 2.9999.9999"
  , "bar" : ">=1.0.2 <2.1.2"
  , "baz" : ">1.0.2 <=2.3.4"
  , "boo" : "2.0.1"
  , "asd" : ""
  , "til" : "~1.2"
  , "elf" : "~1.2.3"
  , "two" : "2.x"
  , "thr" : "3.3.x"
  , "lat" : "latest"
  , "dyl" : "file:../dyl"

URLs as Dependencies

You may specify a tarball URL in place of a version range.

This tarball will be downloaded and installed locally to your package at install time.

Git URLs as Dependencies

Git urls can be of the form:


GitHub URLs

As of version 1.1.65, you can refer to GitHub urls as just "foo": "user/foo-project". Just as with git URLs, a commit-ish suffix can be included. For example:
  "name": "foo",
  "version": "0.0.0",
  "dependencies": {
    "express": "visionmedia/express",
    "mocha": "visionmedia/mocha#4727d357ea"

Local Paths

As of version 2.0.0 you can provide a path to a local directory that contains a package. Local paths can be saved using npm install -S or npm install --save, using any of these forms:

in which case they will be normalized to a relative path and added to your package.json. For example:

  "name": "baz",
  "dependencies": {
    "bar": "file:../foo/bar"

This feature is helpful for local offline development and creating tests that require npm installing where you don't want to hit an external server, but should not be used when publishing packages to the public registry.



In this case, it's best to map these additional items in a devDependencies object.

These things will be installed when doing npm link or npm install from the root of a package, and can be managed like any other npm configuration param. See npm help 7 npm-config for more on the topic.

For build steps that are not platform-specific, such as compiling CoffeeScript or other languages to JavaScript, use the prepublish script to do this, and make the required package a devDependency.

For example:

{ "name": "ethopia-waza",
  "description": "a delightfully fruity coffee varietal",
  "version": "1.2.3",
  "devDependencies": {
    "coffee-script": "~1.6.3"
  "scripts": {
    "prepublish": "coffee -o lib/ -c src/"
  "main": "lib/waza.js"

The prepublish script will be run before publishing, so that users can consume the functionality without requiring them to compile it themselves. In dev mode (ie, locally running npm install), it'll run this script as well, so that you can test it easily.


In some cases, you want to express the compatibility of your package with a host tool or library, while not necessarily doing a require of this host. This is usually referred to as a plugin. Notably, your module may be exposing a specific interface, expected and specified by the host documentation.

For example:

  "name": "tea-latte",
  "version": "1.3.5",
  "peerDependencies": {
    "tea": "2.x"

This ensures your package tea-latte can be installed along with the second major version of the host package tea only. npm install tea-latte could possibly yield the following dependency graph:

|-- tea-latte [at] 1.3.5
|-- tea [at] 2.2.0

NOTE: npm versions 1 and 2 will automatically install peerDependencies if they are not explicitly depended upon higher in the dependency tree. In the next major version of npm (npm@3), this will no longer be the case. You will receive a warning that the peerDependency is not installed instead. The behavior in npms 1 & 2 was frequently confusing and could easily put you into dependency hell, a situation that npm is designed to avoid as much as possible.

Trying to install another plugin with a conflicting requirement will cause an error. For this reason, make sure your plugin requirement is as broad as possible, and not to lock it down to specific patch versions.

Assuming the host complies with semver, only changes in the host package's major version will break your plugin. Thus, if you've worked with every 1.x version of the host package, use "^1.0" or "1.x" to express this. If you depend on features introduced in 1.5.2, use ">= 1.5.2 < 2".


Array of package names that will be bundled when publishing the package.

If this is spelled "bundleDependencies", then that is also honored.


If a dependency can be used, but you would like npm to proceed if it cannot be found or fails to install, then you may put it in the optionalDependencies object. This is a map of package name to version or url, just like the dependencies object. The difference is that build failures do not cause installation to fail.

It is still your program's responsibility to handle the lack of the dependency. For example, something like this:

try {
  var foo = require('foo')
  var fooVersion = require('foo/package.json').version
} catch (er) {
  foo = null
if ( notGoodFooVersion(fooVersion) ) {
  foo = null

// .. then later in your program ..

if (foo) {

Entries in optionalDependencies will override entries of the same name in dependencies, so it's usually best to only put in one place.


You can specify the version of node that your stuff works on:
{ "engines" : { "node" : ">=0.10.3 <0.12" } }



You can also use the "engines" field to specify which versions of npm are capable of properly installing your program. For example:

{ "engines" : { "npm" : "~1.0.20" } }

Note that, unless the user has set the engine-strict config flag, this field is advisory only.


This feature was deprecated with npm 3.0.0

Prior to npm 3.0.0, this feature was used to treat this package as if the user had set engine-strict.


You can specify which operating systems your module will run on:
"os" : [ "darwin", "linux" ]

You can also blacklist instead of whitelist operating systems, just prepend the blacklisted os with a '!':

"os" : [ "!win32" ]

The host operating system is determined by process.platform

It is allowed to both blacklist, and whitelist, although there isn't any good reason to do this.


If your code only runs on certain cpu architectures, you can specify which ones.
"cpu" : [ "x64", "ia32" ]

Like the os option, you can also blacklist architectures:

"cpu" : [ "!arm", "!mips" ]

The host architecture is determined by process.arch


If your package is primarily a command-line application that should be installed globally, then set this value to true to provide a warning if it is installed locally.

It doesn't actually prevent users from installing it locally, but it does help prevent some confusion if it doesn't work as expected.


If you set "private": true in your package.json, then npm will refuse to publish it.

This is a way to prevent accidental publication of private repositories. If you would like to ensure that a given package is only ever published to a specific registry (for example, an internal registry), then use the publishConfig dictionary described below to override the registry config param at publish-time.


This is a set of config values that will be used at publish-time. It's especially handy if you want to set the tag, registry or access, so that you can ensure that a given package is not tagged with "latest", published to the global public registry or that a scoped module is private by default.

Any config values can be overridden, but of course only "tag", "registry" and "access" probably matter for the purposes of publishing.

See npm help 7 npm-config to see the list of config options that can be overridden.


npm will default some values based on package contents.
"scripts":{"preinstall": "node-gyp rebuild"}
If there is a binding.gyp file in the root of your package, npm will default the preinstall command to compile using node-gyp.
"contributors": [...]
If there is an AUTHORS file in the root of your package, npm will treat each line as a Name <email> (url) format, where email and url are optional. Lines which start with a # or are blank, will be ignored.


npm help 7 semver
npm help init
npm help version
npm help config
npm help 7 config
npm help help
npm help 7 faq
npm help install
npm help publish
npm help uninstall