Provided by: npm_3.5.2-0ubuntu4_all 
NAME
package.json - Specifics of npm´s package.json handling
DESCRIPTION
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.
name
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.
• Don´t put "js" or "node" in the name. It´s assumed that it´s js, since you´re writing
a package.json file, and you can specify the engine using the "engines" field. (See
below.)
• The name will probably be passed as an argument to require(), so it should be
something short, but also reasonably descriptive.
• You may want to check the npm registry to see if there´s something by that name
already, before you get too attached to it. https://www.npmjs.com/
A name can be optionally prefixed by a scope, e.g. @myorg/mypackage. See npm help 7
npm-scope for more detail.
version
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.
Version must be parseable by node-semver https://github.com/isaacs/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.
description
Put a description in it. It´s a string. This helps people discover your package, as it´s
listed in npm search.
keywords
Put keywords in it. It´s an array of strings. This helps people discover your package as
it´s listed in npm search.
homepage
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.
bugs
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" : "https://github.com/owner/project/issues"
, "email" : "project@hostname.com"
}
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.
license
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 https://spdx.org/licenses/. Ideally you
should pick one that is OSI http://opensource.org/licenses/alphabetical approved.
If your package is licensed under multiple common licenses, use an SPDX license expression
syntax version 2.0 string http://npmjs.com/package/spdx, 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" : "http://opensource.org/licenses/ISC"
}
}
// Not valid metadata
{ "licenses" :
[
{ "type": "MIT"
, "url": "http://www.opensource.org/licenses/mit-license.php"
}
, { "type": "Apache-2.0"
, "url": "http://opensource.org/licenses/apache2.0.php"
}
]
}
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
The "author" is one person. "contributors" is an array of people. A "person" is an object
with a "name" field and optionally "url" and "email", like this:
{ "name" : "Barney Rubble"
, "email" : "b@rubble.com"
, "url" : "http://barnyrubble.tumblr.com/"
}
Or you can shorten that all into a single string, and npm will parse it for you:
"Barney Rubble <b@rubble.com> (http://barnyrubble.tumblr.com/)"
Both email and url are optional either way.
npm also sets a top-level "maintainers" field with your npm user info.
files
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:
• package.json
• README (and its variants)
• CHANGELOG (and its variants)
• LICENSE / LICENCE
Conversely, some files are always ignored:
• .git
• CVS
• .svn
• .hg
• .lock-wscript
• .wafpickle-N
• *.swp
• .DS_Store
• ._*
• npm-debug.log
main
The main field is a module ID that is the primary entry point to your program. That is, if
your package is named foo, and a user installs it, and then does require("foo"), then your
main module´s exports object will be returned.
This should be a module ID relative to the root of your package folder.
For most modules, it makes the most sense to have a main script and often not much else.
bin
A lot of packages have one or more executable files that they´d like to install into the
PATH. npm makes this pretty easy (in fact, it uses this feature to install the "npm"
executable.)
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" } }
man
Specify either a single file or an array of filenames to put in place for the man program
to find.
If only a single file is provided, then it´s installed such that it is the result from man
<pkgname>, regardless of its actual filename. For example:
{ "name" : "foo"
, "version" : "1.2.3"
, "description" : "A packaged foo fooer for fooing foos"
, "main" : "foo.js"
, "man" : "./man/doc.1"
}
would link the ./man/doc.1 file in such that it is the target for man foo
If the filename doesn´t start with the package name, then it´s prefixed. So, this:
{ "name" : "foo"
, "version" : "1.2.3"
, "description" : "A packaged foo fooer for fooing foos"
, "main" : "foo.js"
, "man" : [ "./man/foo.1", "./man/bar.1" ]
}
will create files to do man foo and man foo-bar.
Man files must end with a number, and optionally a .gz suffix if they are compressed. The
number dictates which man section the file is installed into.
{ "name" : "foo"
, "version" : "1.2.3"
, "description" : "A packaged foo fooer for fooing foos"
, "main" : "foo.js"
, "man" : [ "./man/foo.1", "./man/foo.2" ]
}
will create entries for man foo and man 2 foo
directories
The CommonJS Packages http://wiki.commonjs.org/wiki/Packages/1.0 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 https://registry.npmjs.org/npm/latest, you´ll see that it has
directories for doc, lib, and man.
In the future, this information may be used in other creative ways.
directories.lib
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.
directories.bin
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.
directories.man
A folder that is full of man pages. Sugar to generate a "man" array by walking the folder.
directories.doc
Put markdown files in here. Eventually, these will be displayed nicely, maybe, someday.
directories.example
Put example scripts in here. Someday, it might be exposed in some clever way.
repository
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" : "https://github.com/npm/npm.git"
}
"repository" :
{ "type" : "svn"
, "url" : "https://v8.googlecode.com/svn/trunk/"
}
The URL should be a publicly available (perhaps read-only) url that can be handed directly
to a VCS program without any modification. It should not be a url to an html project page
that you put in your browser. It´s for computers.
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"
scripts
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.
config
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
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
• <=version
• ~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.
• range1 || range2 Passes if either range1 or range2 are satisfied.
• 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"
, "qux" : "<1.0.0 || >=2.3.1 <2.4.5 || >=2.5.2 <3.0.0"
, "asd" : "http://asdf.com/asdf.tar.gz"
, "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:
git://github.com/user/project.git#commit-ish
git+ssh://user@hostname:project.git#commit-ish
git+ssh://user@hostname/project.git#commit-ish
git+http://user@hostname/project/blah.git#commit-ish
git+https://user@hostname/project/blah.git#commit-ish
The commit-ish can be any tag, sha, or branch which can be supplied as an argument to git
checkout. The default is master.
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:
../foo/bar
~/foo/bar
/foo/bar
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.
devDependencies
If someone is planning on downloading and using your module in their program, then they
probably don´t want or need to download and build the external test or documentation
framework that you use.
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/waza.coffee"
},
"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.
peerDependencies
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@1.3.5
|-- tea@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 http://semver.org/, 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".
bundledDependencies
Array of package names that will be bundled when publishing the package.
If this is spelled "bundleDependencies", then that is also honored.
optionalDependencies
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) {
foo.doFooThings()
}
Entries in optionalDependencies will override entries of the same name in dependencies, so
it´s usually best to only put in one place.
engines
You can specify the version of node that your stuff works on:
{ "engines" : { "node" : ">=0.10.3 <0.12" } }
And, like with dependencies, if you don´t specify the version (or if you specify "*" as
the version), then any version of node will do.
If you specify an "engines" field, then npm will require that "node" be somewhere on that
list. If "engines" is omitted, then npm will just assume that it works on node.
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.
engineStrict
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.
os
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.
cpu
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
preferGlobal
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.
private
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.
publishConfig
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.
DEFAULT VALUES
npm will default some values based on package contents.
• "scripts": {"start": "node server.js"}
If there is a server.js file in the root of your package, then npm will default the
start command to node server.js.
• "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.
SEE ALSO
• 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
December 2015 PACKAGE.JSON(5)