content/configuring-npm/package-json.md

---
title: package.json
section: 5
description: 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 [`config`](/using-npm/config).

### name

If you plan to publish your package, the *most* important things in your
package.json are the name and version fields as they will be required. 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. If you don't plan to publish your package, the name and
version fields are optional.

The name is what your thing is called.

Some rules:

* The name must be less than or equal to 214 characters. This includes the
  scope for scoped packages.
* The names of scoped packages can begin with a dot or an underscore. This
  is not permitted without a scope.
* 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
[`scope`](/using-npm/scope) for more detail.

### version

If you plan to publish your package, the *most* important things in your
package.json are the name and version fields as they will be required. 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. If you don't plan to publish your package, the name and
version fields are optional.

Version must be parseable by
[node-semver](https://github.com/npm/node-semver), which is bundled with
npm as a dependency.  (`npm install semver` to use it yourself.)

### 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.

Example:

```json
"homepage": "https://github.com/owner/project#readme"
```

### 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:

```json
{
  "bugs": {
    "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:

```json
{
  "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](https://opensource.org/licenses/) approved.

If your package is licensed under multiple common licenses, use an [SPDX
license expression syntax version 2.0
string](https://spdx.dev/specifications/), like this:

```json
{
  "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 a string value like this one:

```json
{
  "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:

```json
// Not valid metadata
{
  "license" : {
    "type" : "ISC",
    "url" : "https://opensource.org/licenses/ISC"
  }
}

// Not valid metadata
{
  "licenses" : [
    {
      "type": "MIT",
      "url": "https://www.opensource.org/licenses/mit-license.php"
    },
    {
      "type": "Apache-2.0",
      "url": "https://opensource.org/licenses/apache2.0.php"
    }
  ]
}
```

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

```json
{
  "license": "ISC"
}
```

```json
{
  "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:

```json
{
  "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:

```json
{
  "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:

```json
{
  "author": "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.

### funding

You can specify an object containing a URL that provides up-to-date
information about ways to help fund development of your package, or a
string URL, or an array of these:

```json
{
  "funding": {
    "type" : "individual",
    "url" : "http://example.com/donate"
  },

  "funding": {
    "type" : "patreon",
    "url" : "https://www.patreon.com/my-account"
  },

  "funding": "http://example.com/donate",

  "funding": [
    {
      "type" : "individual",
      "url" : "http://example.com/donate"
    },
    "http://example.com/donateAlso",
    {
      "type" : "patreon",
      "url" : "https://www.patreon.com/my-account"
    }
  ]
}
```

Users can use the `npm fund` subcommand to list the `funding` URLs of all
dependencies of their project, direct and indirect. A shortcut to visit
each funding url is also available when providing the project name such as:
`npm fund <projectname>` (when there are multiple URLs, the first one will
be visited)

### files

The optional `files` field is an array of file patterns that describes the
entries to be included when your package is installed as a dependency. File
patterns follow a similar syntax to `.gitignore`, but reversed: including a
file, directory, or glob pattern (`*`, `**/*`, and such) will make it so
that file is included in the tarball when it's packed. Omitting the field
will make it default to `["*"]`, which means it will include all files.

Some special files and directories are also included or excluded regardless
of whether they exist in the `files` array (see below).

You can also provide a `.npmignore` file in the root of your package or in
subdirectories, which will keep files from being included. At the root of
your package it will not override the "files" field, but in subdirectories
it will. The `.npmignore` file works just like a `.gitignore`. If there is
a `.gitignore` file, and `.npmignore` is missing, `.gitignore`'s contents
will be used instead.

Certain files are always included, regardless of settings:

* `package.json`
* `README`
* `LICENSE` / `LICENCE`
* The file in the "main" field
* The file(s) in the "bin" field

`README` & `LICENSE` can have any case and extension.

Some files are always ignored by default:

* `*.orig`
* `.*.swp`
* `.DS_Store`
* `._*`
* `.git`
* `.hg`
* `.lock-wscript`
* `.npmrc`
* `.svn`
* `.wafpickle-N`
* `CVS`
* `config.gypi`
* `node_modules`
* `npm-debug.log`
* `package-lock.json` (use
  [`npm-shrinkwrap.json`](/configuring-npm/npm-shrinkwrap-json)
  if you wish it to be published)
* `pnpm-lock.yaml`
* `yarn.lock`

Most of these ignored files can be included specifically if included in
the `files` globs.  Exceptions to this are:

* `.git`
* `.npmrc`
* `node_modules`
* `package-lock.json`
* `pnpm-lock.yaml`
* `yarn.lock`

These can not be included.

### 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 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.

If `main` is not set, it defaults to `index.js` in the package's root folder.

### browser

If your module is meant to be used client-side the browser field should be
used instead of the main field. This is helpful to hint users that it might
rely on primitives that aren't available in Node.js modules. (e.g.
`window`)

### 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. When this package is installed globally,
that file will be either linked inside the global bins directory or
a cmd (Windows Command File) will be created which executes the specified
file in the `bin` field, so it is available to run by `name` or `name.cmd` (on
Windows PowerShell). When this package is installed as a dependency in another
package, the file will be linked where it will be available to that package
either directly by `npm exec` or by name in other scripts when invoking them
via `npm run-script`.


For example, myapp could have this:

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

So, when you install myapp, in case of unix-like OS it'll create a symlink
from the `cli.js` script to `/usr/local/bin/myapp` and in case of windows it
will create a cmd file usually at `C:\Users\{Username}\AppData\Roaming\npm\myapp.cmd`
which runs the `cli.js` script.

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:

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

would be the same as this:

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

Please make sure that your file(s) referenced in `bin` starts with
`#!/usr/bin/env node`, otherwise the scripts are started without the node
executable!

Note that you can also set the executable files using [directories.bin](#directoriesbin).

See [folders](/configuring-npm/folders#executables) for more info on
executables.

### 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:

```json
{
  "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:

```json
{
  "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.

```json
{
  "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.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.

### 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:

```json
{
  "repository": {
    "type": "git",
    "url": "https://github.com/npm/cli.git"
  }
}
```

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`:

```json
{
  "repository": "npm/npm",

  "repository": "github:user/repo",

  "repository": "gist:11081aaa281",

  "repository": "bitbucket:user/repo",

  "repository": "gitlab:user/repo"
}
```

If the `package.json` for your package is not in the root directory (for
example if it is part of a monorepo), you can specify the directory in
which it lives:

```json
{
  "repository": {
    "type": "git",
    "url": "https://github.com/facebook/react.git",
    "directory": "packages/react-dom"
  }
}
```

### 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 [`scripts`](/using-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:

```json
{
  "name": "foo",
  "config": {
    "port": "8080"
  }
}
```

It could also have a "start" command that referenced the
`npm_package_config_port` environment variable.

### 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 or other "development"
time tools in your `dependencies` object.**  See `devDependencies`, below.

See [semver](https://github.com/npm/node-semver#versions) 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
  [semver](https://github.com/npm/node-semver#versions)
* `^version` "Compatible with version"  See [semver](https://github.com/npm/node-semver#versions)
* `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
  dist-tag`](/commands/npm-dist-tag)
* `path/path/path` See [Local Paths](#local-paths) below

For example, these are all valid:

```json
{
  "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 are of the form:

```bash
<protocol>://[<user>[:<password>]@]<hostname>[:<port>][:][/]<path>[#<commit-ish> | #semver:<semver>]
```

`<protocol>` is one of `git`, `git+ssh`, `git+http`, `git+https`, or
`git+file`.

If `#<commit-ish>` is provided, it will be used to clone exactly that
commit. If the commit-ish has the format `#semver:<semver>`, `<semver>` can
be any valid semver range or exact version, and npm will look for any tags
or refs matching that range in the remote repository, much as it would for
a registry dependency. If neither `#<commit-ish>` or `#semver:<semver>` is
specified, then the default branch is used.

Examples:

```bash
git+ssh://git@github.com:npm/cli.git#v1.0.27
git+ssh://git@github.com:npm/cli#semver:^5.0
git+https://isaacs@github.com/npm/cli.git
git://github.com/npm/cli.git#v1.0.27
```

When installing from a `git` repository, the presence of certain fields in the
`package.json` will cause npm to believe it needs to perform a build. To do so
your repository will be cloned into a temporary directory, all of its deps
installed, relevant scripts run, and the resulting directory packed and
installed.

This flow will occur if your git dependency uses `workspaces`, or if any of the
following scripts are present:

* `build`
* `prepare`
* `prepack`
* `preinstall`
* `install`
* `postinstall`

If your git repository includes pre-built artifacts, you will likely want to
make sure that none of the above scripts are defined, or your dependency
will be rebuilt for every installation.

#### 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:

```json
{
  "name": "foo",
  "version": "0.0.0",
  "dependencies": {
    "express": "expressjs/express",
    "mocha": "mochajs/mocha#4727d357ea",
    "module": "user/repo#feature\/branch"
  }
}
```

#### 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:

```bash
../foo/bar
~/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:

```json
{
  "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 your package to the public registry.

*note*: Packages linked by local path will not have their own
dependencies installed when `npm install` is ran in this case.  You must
run `npm install` from inside the local path itself.

### 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 [`config`](/using-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 `prepare` script to
do this, and make the required package a devDependency.

For example:

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

The `prepare` 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:

```json
{
  "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:

```bash
├── tea-latte@1.3.5
└── tea@2.2.0
```

In npm versions 3 through 6, `peerDependencies` were not automatically
installed, and would raise a warning if an invalid version of the peer
dependency was found in the tree.  As of npm v7, peerDependencies _are_
installed by default.

Trying to install another plugin with a conflicting requirement may cause
an error if the tree cannot be resolved correctly. 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](https://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"`.

### peerDependenciesMeta

When a user installs your package, npm will emit warnings if packages
specified in `peerDependencies` are not already installed. The
`peerDependenciesMeta` field serves to provide npm more information on how
your peer dependencies are to be used. Specifically, it allows peer
dependencies to be marked as optional.

For example:

```json
{
  "name": "tea-latte",
  "version": "1.3.5",
  "peerDependencies": {
    "tea": "2.x",
    "soy-milk": "1.2"
  },
  "peerDependenciesMeta": {
    "soy-milk": {
      "optional": true
    }
  }
}
```

Marking a peer dependency as optional ensures npm will not emit a warning
if the `soy-milk` package is not installed on the host. This allows you to
integrate and interact with a variety of host packages without requiring
all of them to be installed.

### bundleDependencies

This defines an array of package names that will be bundled when publishing
the package.

In cases where you need to preserve npm packages locally or have them
available through a single file download, you can bundle the packages in a
tarball file by specifying the package names in the `bundleDependencies`
array and executing `npm pack`.

For example:

If we define a package.json like this:

```json
{
  "name": "awesome-web-framework",
  "version": "1.0.0",
  "bundleDependencies": [
    "renderized",
    "super-streams"
  ]
}
```

we can obtain `awesome-web-framework-1.0.0.tgz` file by running `npm pack`.
This file contains the dependencies `renderized` and `super-streams` which
can be installed in a new project by executing `npm install
awesome-web-framework-1.0.0.tgz`.  Note that the package names do not
include any versions, as that information is specified in `dependencies`.

If this is spelled `"bundledDependencies"`, then that is also honored.

Alternatively, `"bundleDependencies"` can be defined as a boolean value. A
value of `true` will bundle all dependencies, a value of `false` will bundle
none.

### 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.  Running `npm install
--omit=optional` will prevent these dependencies from being installed.

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

```js
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.

### overrides

If you need to make specific changes to dependencies of your dependencies, for
example replacing the version of a dependency with a known security issue,
replacing an existing dependency with a fork, or making sure that the same
version of a package is used everywhere, then you may add an override.

Overrides provide a way to replace a package in your dependency tree with
another version, or another package entirely. These changes can be scoped as
specific or as vague as desired.

To make sure the package `foo` is always installed as version `1.0.0` no matter
what version your dependencies rely on:

```json
{
  "overrides": {
    "foo": "1.0.0"
  }
}
```

The above is a short hand notation, the full object form can be used to allow
overriding a package itself as well as a child of the package. This will cause
`foo` to always be `1.0.0` while also making `bar` at any depth beyond `foo`
also `1.0.0`:

```json
{
  "overrides": {
    "foo": {
      ".": "1.0.0",
      "bar": "1.0.0"
    }
  }
}
```

To only override `foo` to be `1.0.0` when it's a child (or grandchild, or great
grandchild, etc) of the package `bar`:

```json
{
  "overrides": {
    "bar": {
      "foo": "1.0.0"
    }
  }
}
```

Keys can be nested to any arbitrary length. To override `foo` only when it's a
child of `bar` and only when `bar` is a child of `baz`:

```json
{
  "overrides": {
    "baz": {
      "bar": {
        "foo": "1.0.0"
      }
    }
  }
}
```

The key of an override can also include a version, or range of versions.
To override `foo` to `1.0.0`, but only when it's a child of `bar@2.0.0`:

```json
{
  "overrides": {
    "bar@2.0.0": {
      "foo": "1.0.0"
    }
  }
}
```

You may not set an override for a package that you directly depend on unless
both the dependency and the override itself share the exact same spec. To make
this limitation easier to deal with, overrides may also be defined as a
reference to a spec for a direct dependency by prefixing the name of the
package you wish the version to match with a `$`.

```json
{
  "dependencies": {
    "foo": "^1.0.0"
  },
  "overrides": {
    // BAD, will throw an EOVERRIDE error
    // "foo": "^2.0.0"
    // GOOD, specs match so override is allowed
    // "foo": "^1.0.0"
    // BEST, the override is defined as a reference to the dependency
    "foo": "$foo",
    // the referenced package does not need to match the overridden one
    "bar": "$foo"
  }
}
```

### engines

You can specify the version of node that your stuff works on:

```json
{
  "engines": {
    "node": ">=0.10.3 <15"
  }
}
```

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.

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

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

Unless the user has set the
[`engine-strict` config](/using-npm/config#engine-strict) flag, this field is
advisory only and will only produce warnings when your package is installed as a
dependency.

### os

You can specify which operating systems your
module will run on:

```json
{
  "os": [
    "darwin",
    "linux"
  ]
}
```

You can also block instead of allowing operating systems, just prepend the
blocked os with a '!':

```json
{
  "os": [
    "!win32"
  ]
}
```

The host operating system is determined by `process.platform`

It is allowed to both block and allow an item, 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.

```json
{
  "cpu": [
    "x64",
    "ia32"
  ]
}
```

Like the `os` option, you can also block architectures:

```json
{
  "cpu": [
    "!arm",
    "!mips"
  ]
}
```

The host architecture is determined by `process.arch`

### 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.

See [`config`](/using-npm/config) to see the list of config options that
can be overridden.

### workspaces

The optional `workspaces` field is an array of file patterns that describes
locations within the local file system that the install client should look
up to find each [workspace](/using-npm/workspaces) that needs to be
symlinked to the top level `node_modules` folder.

It can describe either the direct paths of the folders to be used as
workspaces or it can define globs that will resolve to these same folders.

In the following example, all folders located inside the folder
`./packages` will be treated as workspaces as long as they have valid
`package.json` files inside them:

```json
{
  "name": "workspace-example",
  "workspaces": [
    "./packages/*"
  ]
}
```

See [`workspaces`](/using-npm/workspaces) for more examples.

### 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":{"install": "node-gyp rebuild"}`

  If there is a `binding.gyp` file in the root of your package and you have
  not defined an `install` or `preinstall` script, npm will default the
  `install` 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

* [semver](https://github.com/npm/node-semver#versions)
* [workspaces](/using-npm/workspaces)
* [npm init](/commands/npm-init)
* [npm version](/commands/npm-version)
* [npm config](/commands/npm-config)
* [npm help](/commands/npm-help)
* [npm install](/commands/npm-install)
* [npm publish](/commands/npm-publish)
* [npm uninstall](/commands/npm-uninstall)