PACKAGE.JSON(5)

🌸 NAME 🌸

package.json — the specifics of npm's package.json handling, aka the PACKAGE.JSON(5) manual page, bestie. We're doing this. 💅

✨ DESCRIPTION ✨

Okay so this document is literally 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 less than or equal to 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 https://opensource.org/licenses/alphabetical approved.

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

         { "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
• CHANGES / CHANGELOG / HISTORY (any casing and file extension)
• LICENSE / LICENCE
• The file in the "main" field

Conversely, some files are always ignored:

• .git
• CVS
• .svn
• .hg
• .lock-wscript
• .wafpickle-N
• .*.swp
• .DS_Store
• ._*
• npm-debug.log
• .npmrc
• node_modules

⭐ 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" } }

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! 💀

🌸 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 🎀

ok so the CommonJS Packages spec (http://wiki.commonjs.org/wiki/Packages/1.0) lays out a couple ways you can show off the structure of your package with a directories object. if you peek at npm's own package.json (https://registry.npmjs.org/npm/latest) you'll see it's got directories for doc, lib, and man. slay.

and like — in the future this info might get used in other creative ways. no promises, but the potential is giving main character energy ✨

directories.lib

this is where you tell the people where the bulk of your library lives. nothing special happens to the lib folder, like, at all — but it's useful meta info. lowkey just a vibe marker 🫶

directories.bin

if you specify a bin directory in directories.bin, all the files in that folder get added. iconic, no cap.

🚨 but heads up bestie: because of how the bin directive works, specifying both a bin path and setting directories.bin is an error. pick one. if you want individual files, use bin; if you want every file in an existing bin directory, use directories.bin. that's the whole vibe check.

directories.man

a folder literally full of man pages. it's sugar that generates a "man" array by walking through the folder for you. so convenient honestly 🌸

directories.doc

put your markdown files in here. eventually they'll be displayed nicely — maybe. someday. 😭 (the optimism is cute)

directories.example

put example scripts in here. someday it might be exposed in some clever way. we're manifesting 🙈

directories.test

put your tests in here. currently it's not exposed, but it might be in the future. keeping the dream alive 💜

---

🦋 repository 🦋

this is where you specify the place where your code lives. it's a whole thing for people who want to contribute — super helpful. and if your git repo is on GitHub, the npm docs command will literally be able to find you. iconic behavior.

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 (maybe 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'd put in your browser. it's for computers, bestie. computers. 💅

for GitHub, GitHub gist, Bitbucket, or GitLab repositories you can use the same shortcut syntax you already 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 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. simple as that, periodt.

see npm help 7 npm-scripts to find out more about writing package scripts. go read it, i'll wait 🫶

---

🌈 config 🌈

a "config" object can be used to set configuration parameters used in package scripts that persist across upgrades. so like, set it once and it stays. queen behavior.

for instance, if a package had the following:

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

and then had a "start" command that 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 with one or more space-separated descriptors. dependencies can also be identified with a tarball or git URL. flexible, we love that.

🙅‍♀️ please do not put test harnesses or transpilers in your dependencies object. see devDependencies, below. keep it clean bestie.

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 — less than, obviously
• <=version — less than or equal
• ~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 #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. boom, done 🔥

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. classic.

---

🧚 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 --save, using any of these forms:

../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:

{
  "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 it should not be used when publishing packages to the public registry. do not do it. i'm serious. that's the danger zone.

---

💜 devDependencies 💜

okay so 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. like, respectfully, they're here for the module.

in this case, it's best to map these additional items in a devDependencies object. keep them separated, it's giving organized 💖

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 — like 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. and in dev mode (ie, locally running npm install), it'll run this script as well, so you can test it easily. best of both worlds, genuinely iconic 🌸

---

🎀 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. iykyk.

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. please. for everyone's sake 🙏

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 ✨

this defines an array of package names that will be bundled when publishing the package. bundling, bundling, bundling 🎁

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 bundledDependencies array and executing npm pack.

for example: if we define a package.json like this:

{
  "name": "awesome-web-framework",
  "version": "1.0.0",
  "bundledDependencies": [
    '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. one file, everything inside, no cap 🔥

and if this is spelled "bundleDependencies", then that is also honored. yes, both spellings eat. 👑

🍓 optionalDependencies 🍓

okay so bestie, picture dependencies but ✨chill✨. If a dep can be used but you'd rather npm just keep it moving when it can't be found or flat-out fails to install, you drop it in the optionalDependencies object. It's a map of package name to version or url, literally just like the dependencies object. The one difference? build failures do not cause installation to fail. slay.

That said, it's still your program's responsibility to handle the lack of the dependency. no cap. Something like this, for example:

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()
}

Also important 🫶: entries in optionalDependencies will override entries of the same name in dependencies, so it's usually best to only put it in one place. pick a lane bestie 💅

---

🧚 engines 🧚

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

{ "engines" : { "node" : ">=0.10.3 <0.12" } }

And, just like with dependencies, if you don't specify the version (or if you specify "*" as the version), then any version of node will do. very demure, very unbothered.

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. trust falls 😌

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

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

heads up: unless the user has set the engine-strict config flag, this field is advisory only and will produce warnings when your package is installed as a dependency. it's giving "suggestion box", not "bouncer" 💀

---

💀 engineStrict 💀

NOTE: this feature is deprecated and will be removed in npm 3.0.0. like, genuinely deprecated, not cute-deprecated.

If you are sure that your module will definitely not run properly on versions of Node/npm other than those specified in the engines object, then you can set "engineStrict": true in your package.json file. This will override the user's engine-strict config setting. 😳

Please do not do this unless you are really very very sure. If your engines object is something overly restrictive, you can quite easily and inadvertently lock yourself into obscurity and prevent your users from updating to new versions of Node. Consider this choice carefully. fr fr, this is the unglamorous kind of main character energy 🙈

---

🦋 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. it's giving mixed signals bestie 💅

---

🌈 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. it's a vibe check, not a lock 🔒

---

🙈 private 🙈

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

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. iykyk 🎀

---

💜 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. iconic little safety net honestly ✨

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. the little automatic touches, we love her 🫶

• "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 🎀

the lil reading list, go off bestie:

• 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

---

and that's the whole page, bestie, you made it 🥹💖 this was PACKAGE.JSON(5) from the npm docs, dated March 2017 — go forth and write the most immaculate package.json of your life. mwah 💅✨