PACKAGE.JSON(5)

📦
version 12.2.1 · 23 versions
, in arch rolling

💖 NAME 💖

package.json — welcome to the PACKAGE.JSON(5) manual page, bestie! 🎀 This is literally all about the specifics of npm's package.json handling, and yes, we're gonna get into it.

✨ Description ✨

okay so, this document? it's genuinely everything you need to know about what's required in your package.json file. no cap. 🫶

One thing though — it must be actual JSON. Not just a JavaScript object literal. Real JSON. periodt. 💅

Also important: a lot of the behavior described in this document is affected by the config settings described in npm help config. So keep that in mind, iykyk.

🌸 name 🌸

If you're planning to publish your package, the most important things in your package.json are the name and version fields, because they're gonna be required. The name and version together form an identifier that's assumed to be completely unique. Changes to the package should come along with changes to the version. If you're not planning to publish your package, the name and version fields are optional — no pressure. 🌈

The name is what your thing is called. main character energy, honestly. 👑

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. just don't 🙈
  • 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. @npm/example. See npm help scope for more detail. ✨

🦋 version 🦋

(same opening as above, bestie — it's the same rule, just showing up twice 💀) 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 version must be parseable by node-semver (https://github.com/npm/node-semver), which is bundled with npm as a dependency. You can npm install semver to use it yourself. 🎀

🎀 description 🎀

Put a description in it. It's a string. This helps people discover your package, since it's listed in npm search. literally free clout. 🔥

⭐ keywords ⭐

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

Example:

"keywords": [
  "node",
  "javascript",
  "npm"
]

🌈 homepage 🌈

The URL to the project homepage. 🏠

Example:

"homepage": "https://github.com/npm/example#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 — so they know where to yell, kindly. 🫶

It should look like this:

{
  "bugs": {
    "url": "https://github.com/npm/example/issues",
    "email": "example@npmjs.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. easy peasy. ✨

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're permitted to use it, and any restrictions you're placing on it. Like, protect your work, bestie. 💅

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 at 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:

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

If you're using a license that hasn't been assigned an SPDX identifier, or if you're 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" : "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, jsyk. 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. like, please, save yourself the embarrassment 🙈

🫶 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" : "barney@npmjs.com",
  "url" : "http://barnyrubble.npmjs.com/"
}

Or you can shorten that all into a single string, and npm will parse it for you:

{
  "author": "Barney Rubble <barney@npmjs.com> (http://barnyrubble.npmjs.com/)"
}

Both email and url are optional either way. easy. ✨

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, a string URL, or an array of objects and string URLs. get that bag, bestie 💖

{
  "funding": {
    "type" : "individual",
    "url" : "http://npmjs.com/donate"
  }
}
{
  "funding": {
    "type" : "patreon",
    "url" : "https://www.patreon.com/user"
  }
}
{
  "funding": "http://npmjs.com/donate"
}
{
  "funding": [
    {
      "type" : "individual",
      "url" : "http://npmjs.com/donate"
    },
    "http://npmjs.com/donate-also",
    {
      "type" : "patreon",
      "url" : "https://www.patreon.com/user"
    }
  ]
}

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
  • pnpm-lock.yaml
  • yarn.lock
  • bun.lockb

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
  • bun.lockb

These cannot be included. like, at all. sorry bestie 💀

🚪 exports 🚪

The "exports" field provides a modern alternative to "main", allowing multiple entry points to be defined, conditional entry resolution support between environments, and preventing any other entry points besides those defined in "exports". This encapsulation allows module authors to clearly define the public interface for their package. For more details see the node.js documentation on package entry points at https://nodejs.org/api/packages.html#package-entry-points. 👑

🚪 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. literally the front door of your whole package. 🏠

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. ✨

🎀 type 🎀

The type field defines how Node.js should interpret .js files in your package. This field is not used by npm.

See the Node.js documentation on the type field at https://nodejs.org/api/packages.html#type for more information. 🦋

🦋 browser 🦋

Okay so if your module is meant to be used client-side, you use the browser field instead of the main field. Lowkey iconic of it. It's genuinely helpful because it hints to users that your thing might rely on primitives that aren't available in Node.js modules (e.g. window). Like, bestie, that's a browser thing, the Node girlies can't help you there 💅

🎀 bin 🎀

A lot of packages have one or more executable files they'd like to install into the PATH. npm makes this pretty easy (in fact, it uses this feature itself to install the "npm" executable). Main character behavior, honestly.

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's 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.

For example, myapp could have this:

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

So, when you install myapp, in case of a 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. Slay 🔥

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"
  }
}
⚠️ bestie 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! 😭 That's the classic "why is my CLI doing weird stuff" moment and we are NOT doing that.

Note that you can also set the executable files using (directories.bin).

See folders ⟨/configuring-npm/folders#executables⟩ for more info on executables 🫶

🧚 man 🧚

Note: As of npm v12, man pages are no longer registered with the system man program. This field is retained for backward compatibility with package metadata and tools that consume it, but man <pkgname> will not work after a global install. Use npm help <pkgname> instead where supported. 💀

Specify either a single file or an array of filenames to include as man pages.

If only a single file is provided, then it corresponds to 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 associate the ./man/doc.1 file 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 correspond to 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 belongs to 📚

{
  "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. She's organized, she's got her life together 💖

In the future, this information may be used in other creative ways. 👀 (mysterious, love that for us)

✨ 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 🚨 Like, pick a lane bestie. 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 🍓

See the note on man (man) above: as of npm v12, these are no longer installed into the system man path.

🦋 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 repo command will be able to find you. Iconic.

Do it like this:

{
  "repository": {
    "type": "git",
    "url": "git+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 🤖 ngl that's the whole vibe check of this field.

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

{
  "repository": "npm/example",

  "repository": "github:npm/example",

  "repository": "gist:11081aaa281",

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

  "repository": "gitlab:user/repo"
}
Note on normalization: When you publish a package, npm normalizes the repository field to the full object format with a url property. If you use a shorthand format (like "npm/example"), you'll see a warning during npm publish indicating that the field was auto-corrected. While the shorthand format currently works, it's recommended to use the full object format in your package.json to avoid warnings and ensure future compatibility:
{
  "repository": {
    "type": "git",
    "url": "git+https://github.com/npm/example.git"
  }
}

You can run npm pkg fix to automatically convert shorthand formats to the normalized object format. Fix it in one command, we love a glow-up ✨

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:

{
  "repository": {
    "type": "git",
    "url": "git+https://github.com/npm/cli.git",
    "directory": "workspaces/libnpmpublish"
  }
}

🧚 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 scripts to find out more about writing package scripts.

💜 gypfile 💜

If you have a binding.gyp file in the root of your package and you have not defined your own install or preinstall scripts, npm will default to building your module using node-gyp 🔨

To prevent npm from automatically building your module with node-gyp, set gypfile to false:

{
  "gypfile": false
}

This is useful for packages that include native addons but want to handle the build process differently, or packages that have a binding.gyp file but should not be built as a native addon. Sometimes you gotta do your own thing, and that's valid 💅

🍓 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"
  }
}

It could also have a "start" script 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.

Do NOT put test harnesses or transpilers or other "development" time tools in your dependencies object. 💀 See devDependencies, below. Keep the bins clean bestie.

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 help dist-tag
  • path/path/path — see (Local Paths) below
  • npm:@scope/pkg@version — custom alias for a package — see package-spec ⟨/using-npm/package-spec#aliases⟩

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://npmjs.com/example.tar.gz",
    "til": "~1.2",
    "elf": "~1.2.3",
    "two": "2.x",
    "thr": "3.3.x",
    "lat": "latest",
    "dyl": "file:../dyl",
    "kpg": "npm:pkg@1.0.0"
  }
}

⭐ 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:

<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:

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

Okay so real talk about git installs 🫶 when you install from a git repo, npm peeks at your package.json and if it spots certain fields it goes "ohhh we're building this one" and lowkey commits to the whole production. It clones your repo into a temporary directory, installs all of its deps, runs the relevant scripts, then packs up the resulting directory and installs that. Full glow-up pipeline ✨

This whole flow kicks in if your git dependency uses workspaces, or if any of these scripts are present:

  • build
  • prepare
  • prepack
  • preinstall
  • install
  • postinstall

So if your git repo already ships pre-built artifacts, bestie you are gonna want to make sure none of the above scripts are defined — otherwise your dependency gets rebuilt on every single installation. Every. Single. One. 😭 Not the vibe.

🌈 GitHub URLs 🌈

As of version 1.1.65, you can refer to GitHub URLs as just "foo": "user/foo-project". And just like with git URLs, you can tack a commit-ish suffix on the end. Like so:

{
  "name": "foo",
  "version": "0.0.0",
  "dependencies": {
    "express": "expressjs/express",
    "mocha": "mochajs/mocha#4727d357ea",
    "module": "npm/example-github-repo#feature\/branch"
  }
}

🎀 Local Paths 🎀

As of version 2.0.0 you can hand npm 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

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

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

This feature is so helpful for local offline development and for creating tests that require npm installing where you don't wanna hit an external server. But do not use it when publishing your package to the public registry. Periodt.

note: packages linked by local path will not have their own dependencies installed when npm install is run. You must run npm install from inside the local path itself. iykyk 💅

🦋 devDependencies 🦋

If someone's 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 you use. Like, they just want your code, not your whole backstage 😭

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 config for more on the topic.

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

For example:

{
  "name": "@npm/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. And in dev mode (ie, locally running npm install), it'll run this script as well, so you can test it easily. Convenient?? We love to see it 💖

💜 peerDependencies 💜

Sometimes 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": "@npm/tea-latte",
  "version": "1.3.5",
  "peerDependencies": {
    "@npm/tea": "2.x"
  }
}

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

├── @npm/tea-latte@1.3.5
└── @npm/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. Glow-up era ✨

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 don't lock it down to specific patch versions. Be chill about it 🙏

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 🍓

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. Npm will not automatically install optional peer dependencies. This lets you integrate and interact with a variety of host packages without requiring all of them to be installed. Honestly? Iconic design 💅

For example:

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

🧚 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:

{
  "name": "@npm/awesome-web-framework",
  "version": "1.0.0",
  "bundleDependencies": [
    "@npm/renderized",
    "@npm/super-streams"
  ]
}

we can obtain @npm/awesome-web-framework-1.0.0.tgz file by running npm pack. This file contains the dependencies @npm/renderized and @npm/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. (Yes, both spellings, we're flexible like that 😌)

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.

For example:

{
  "optionalDependencies": {
    "@npm/foo": "^1.0.0"
  }
}

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

try {
  var foo = require('@npm/foo')
  var fooVersion = require('@npm/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. Don't be out here duplicating, bestie 🙈

👑 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. Your tree, your rules 💅

Overrides are only considered in the root package.json file for a project. Overrides in installed dependencies (including npm help workspaces) are not considered in dependency tree resolution. Published packages may dictate their resolutions by pinning dependencies or using bundleDependencies (bundleDependencies).

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

{
  "overrides": {
    "@npm/foo": "1.0.0"
  }
}

Override values can use any specifier that npm accepts for dependencies, including an exact version, a semver range, a dist-tag, or a replacement specifier such as npm:, file:, or a Git URL.

For example, if you only need to enforce a minimum patched release instead of one exact version, you can use a semver range:

{
  "overrides": {
    "@npm/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 @npm/foo to always be 1.0.0 while also making @npm/bar at any depth beyond @npm/foo also 1.0.0:

{
  "overrides": {
    "@npm/foo": {
      ".": "1.0.0",
      "@npm/bar": "1.0.0"
    }
  }
}

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

{
  "overrides": {
    "@npm/bar": {
      "@npm/foo": "1.0.0"
    }
  }
}

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

{
  "overrides": {
    "@npm/baz": {
      "@npm/bar": {
        "@npm/foo": "1.0.0"
      }
    }
  }
}

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

So like, nested-style, you can go deeper — here's @npm/bar@2.0.0 getting its own little override world where @npm/foo is pinned to 1.0.0 💅

{
  "overrides": {
    "@npm/bar@2.0.0": {
      "@npm/foo": "1.0.0"
    }
  }
}

Okay and this next bit is important, bestie, don't skip it 🫶 You are not allowed to set an override for a package you directly depend on unless the dependency and the override itself share the exact same spec. But because that's kind of annoying, overrides can also be defined as a reference to a spec for a direct dependency — you just prefix the name of the package whose version you want to match with a $. Iconic. ✨

{
  "dependencies": {
    "@npm/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
    "@npm/foo": "$foo",
    // the referenced package does not need to match the overridden one
    "@npm/bar": "$foo"
  }
}

💅 Replacing a dependency with a fork

Okay so this is genuinely one of the coolest things here — you can swap a package out for a completely different package or a fork. There are several methods:

Using the npm: prefix to replace with a different package name:

{
  "overrides": {
    "package-name": "npm:@scope/forked-package@1.0.0"
  }
}

Using a GitHub repository (supports branches, tags, or commit hashes):

{
  "overrides": {
    "package-name": "github:username/repo#branch-name"
  }
}

Using a local file path:

{
  "overrides": {
    "package-name": "file:../local-fork"
  }
}

These replacement methods work for both top-level overrides and nested overrides. Like, for example, to replace a transitive dependency with a fork:

{
  "overrides": {
    "parent-package": {
      "vulnerable-dep": "github:username/patched-fork#v2.0.1"
    }
  }
}

🧚 packageExtensions

So packageExtensions lets a project apply small, declarative repairs to the manifests of third-party dependencies before npm resolves the dependency tree. Use it to add a missing dependencies, optionalDependencies, or peerDependencies entry, or to correct peerDependencies and peerDependenciesMeta, while you wait for the upstream package to publish a fix. Basically a band-aid for someone else's oopsie 🩹

This is especially useful with install-strategy=linked ⟨/using-npm/config#install-strategy⟩, where dependencies are fully isolated and a package only sees what it actually declared. A package that worked under a hoisted layout because a dependency happened to be hoisted above it can fail under linked; packageExtensions records the missing edge as explicit, reviewable, root-owned policy. No cap. 👑

packageExtensions complements overrides (overrides): overrides changes what an existing dependency edge resolves to, while packageExtensions adds or corrects the dependency metadata that creates the edge in the first place. For changing the resolved version of a dependency that is already declared, use overrides.

Like overrides, packageExtensions is only honored in the root package.json of a project (the workspace root in a workspace). The field in installed dependencies and in non-root workspace packages is ignored. And because it's root-only project policy, npm refuses to publish a non-private package that contains packageExtensions; it remains available to private packages and unpublished local projects. Rude? Maybe. Sensible? Absolutely. 💀

Each key is a package selector: a package name with an optional semver range.

{
  "packageExtensions": {
    "broken-package@1": {
      "dependencies": {
        "missing-runtime-dep": "^2.0.0"
      }
    },
    "typescript-plugin@4.3.0": {
      "peerDependencies": {
        "typescript": ">=5"
      },
      "peerDependenciesMeta": {
        "typescript": {
          "optional": true
        }
      }
    },
    "@scope/uses-types@2": {
      "dependencies": {
        "@types/node": "^22.0.0"
      }
    }
  }
}
  • "foo" matches all versions of foo.
  • "foo@1" matches versions satisfying 1.
  • "@scope/foo@^2.3.0" matches versions satisfying ^2.3.0.

Selectors match a candidate package's own name and version. They do not accept dist-tags, git, file, directory, URL, or npm: alias specs. For aliases, the selector matches the underlying package name. At most one selector may match a given package; overlapping selectors that both match the same package fail the install. 🙈

Only dependencies, optionalDependencies, peerDependencies, and peerDependenciesMeta may be extended. The merge rules are:

  • dependencies and optionalDependencies entries add a missing dependency only. Adding a name that the package already declares in either field is an error; use overrides to change a version.
  • peerDependencies entries are merged by name, replacing an existing range.
  • peerDependenciesMeta entries are merged by name and then by key, so you can add optional: true without dropping other metadata. Every peerDependenciesMeta entry must correspond to a peerDependencies entry.

Deletion is not supported; a null, false, or "-" value is an error. 🚫

packageExtensions does not rewrite the installed package's package.json on disk and does not modify bundleDependencies. Affected packages are recorded in package-lock.json and surfaced by npm help explain and npm help ls, so each repair is easy to audit and to remove once upstream is fixed. Cleanup queen behavior fr fr 🌸

🦋 engines

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

{
  "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. Whatever works 💁‍♀️

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"
  }
}

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. So like... it's giving suggestion, not enforcement 🎀

⭐ os

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

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

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

{
  "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. Like, technically legal, spiritually chaotic 💀

🌈 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 block architectures:

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

The host architecture is determined by process.arch

💜 libc

If your code only runs or builds in certain versions of libc, you can specify which ones. This field only applies if os is linux.

{
  "os": "linux",
  "libc": "glibc"
}

🎀 devEngines

The devEngines field aids engineers working on a codebase to all be using the same tooling. Teamwork makes the dream work, bestie 🤝

You can specify a devEngines property in your package.json which will run before install, ci, and run commands.

Note: engines and devEngines differ in object shape. They also function very differently. engines is designed to alert the user when a dependency uses a different npm or node version than the project it's being used in, whereas devEngines is used to alert people interacting with the source code of a project. Two completely different vibes, iykyk 💅

The supported keys under the devEngines property are cpu, os, libc, runtime, and packageManager. Each property can be an object or an array of objects. Objects must contain name, and optionally can specify version, and onFail. onFail can be warn, error, or ignore, and if left undefined is of the same value as error. npm will assume that you're running with node. Here's an example of a project that will fail if the environment is not node and npm. If you set runtime.name or packageManager.name to any other string, it will fail within the npm CLI. 😭

{
  "devEngines": {
    "runtime": {
      "name": "node",
      "onFail": "error"
    },
    "packageManager": {
      "name": "npm",
      "onFail": "error"
    }
  }
}

🔥 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.

💖 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. Protect your babies 🫶

See npm help 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 npm help workspace 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:

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

See npm help workspaces for more examples.

✨ DEFAULT VALUES ✨

npm will default some values based on package contents. Little freebies, no notes 💝

  • "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": [...]

Like, if your package has an AUTHORS file sitting in the root, npm will literally read every single line of it as Name <email> (url) — and plot twist, the email and the url are both optional, so a plain old name on its own is totally valid 💅. Lines that start with #? Ignored. Blank lines? Also ignored. No cap, npm just vibes right past them ✨.

🌈 SEE ALSO 💫

  • semver ⟨https://github.com/npm/node-semver#versions⟩ — the whole versioning bible, go read it bestie 📖
  • npm help workspaces — for when one package just isn't enough 🗂️
  • npm help init — the "start from scratch" era 🌱
  • npm help version — bumping numbers like it's a personality trait 🔢
  • npm help config — every knob and dial, all in one place ⚙️
  • npm help help — help-ception, iconic behavior honestly 🫶
  • npm help install — the one you'll be typing forever 😭
  • npm help publish — the main character moment, sending it out into the world 👑
  • npm help uninstall — breaking up with a dependency, it's giving closure 💔

okay that's the whole page, you made it to the end bestie!! 🎀✨ This gorgeous little manual is brought to you by npm@12.2.1, dated October 2026, and filed under PACKAGE.JSON(5) — go forth and slay your package.json 💖🦋🌸

📦 where this page comes from