Learn about our RFC process, Open RFC meetings & more.Join in the discussion! »


3.1.0 • Public • Published


Builds: Node.js CI

This package only works with Yarn v1. Yarn v2 supports package deduplication natively!

Cleans up yarn.lock by removing duplicates.

A duplicate package is when two dependencies are resolved to a different version, even when a single version matches the range specified in the dependencies. See the Deduplication strategies section for a few examples.


Install the package globally:

npm install -g yarn-deduplicate


yarn global add yarn-deduplicate

This package also works wth npx, so you don't need to install it.


The most common scenario is to run

yarn-deduplicate yarn.lock

This will use the default strategy to remove duplicated packages in yarn.lock.

If you do not specify the yarn.lock path, it defaults to yarn.lock.

Check all available options with:

yarn-deduplicate --help

Duplicated packages

yarn.lock contains a list of all the dependencies required by your project (including transitive dependencies), and the actual package version installed to satisfy those dependencies.

For the context of this project, a "duplicated package" is a package that appears on multiple nodes of the dependency tree with overlapping version ranges but resolved to different versions.

For example, imagine that your project directly depends on lodash and babel, and babel depends on lodash as well. Specifically, your project depends on lodash@^1.0.0 and babel depends on lodash@^1.1.0. Because how the resolution algorithm works in Yarn, you might end up with two different copies of lodash (for example, version 1.0.1 and 1.2.0) in your project, even when 1.2.0 will suffice to satisfy both requirements for lodash. That's a "duplicated package".

It is important to note that we do not consider duplicated packages when the version ranges don't overlap. For example, if your project depends on underscore@^1.0.0 and underscore@^2.0.0. Your project will end up with two versions of underscore, and yarn-deduplicate won't change that.

When using yarn-deduplicate remember that it will change your dependency tree. There are certain code paths that now will run with a different set of dependencies. It is highly recommended that you review each change to yarn.lock. If the change is too big, use the flag --packages to deduplicate them gradually.

Why is this necessary?

Yarn documentation seems to suggest this package shouldn't be necessary. For example, in https://classic.yarnpkg.com/en/docs/cli/dedupe/, it says

The dedupe command isn’t necessary. yarn install will already dedupe.

This is, however, not exactly true. There are cases where yarn will not deduplicate existing packages. For example, this scenario:

  • Install libA. It depends on libB ^1.1.0. At this point, the latest version of libB is 1.1.2, so it gets installed as a transitive dependency in your repo

  • After a few days, install libC. It also depends on libB ^1.1.0. But this time, the latest libB version is 1.1.3.

In the above scenario, you'll end up with libB@1.1.2 and libB@1.1.3 in your repo.

Find more examples in:

Deduplication strategies

--strategy <strategy>

highest will try to use the highest installed version. For example, with the following yarn.lock:

  version "1.2.0"
  version "1.2.0"
  version "1.3.0"

It will deduplicate library@^1.1.0 and library@^1.2.0 to 1.3.0

fewer will try to minimize the number of installed versions by trying to deduplicate to the version that satisfies most of the ranges first. For example, with the following yarn.lock:

  version "2.0.0"
  version "3.0.0"
  version "1.2.0"

It will deduplicate library@* and library@>=1.1.0 to 1.2.0.

Note that this may cause some packages to be downgraded. Be sure to check the changelogs between all versions and understand the consequences of that downgrade. If unsure, don't use this strategy.

It is not recommended to use different strategies for different packages. There is no guarantee that the strategy will be honored in subsequent runs of yarn-deduplicate unless the same set of flags is specified again.

Progressive deduplication

--packages <package1> <package2> <packageN>

Receives a list of packages to deduplicate. It will ignore any other duplicated package not in the list. This option is recommended when the number of duplicated packages in yarn.lock is too big to be easily reviewed by a human. This will allow for a more controlled and progressive deduplication of yarn.lock.

--scopes <scope1> <scope2> <scopeN>

Receives a list of scopes to deduplicate. It will ignore any other duplicated package not in the list. This option is recommended when deduplicating a large number of inter-dependent packages from a single scope, such as @babel. This will allow for a more controlled and progressive deduplication of yarn.lock without specifying each package individually.

Pre-release versions

By default, yarn-deduplicate will only match pre-release versions if they share they share the same mayor, minor and patch versions (example: ^1.2.3-alpha.1 and 1.2.3-alpha.2 can be deduplicated, but ^1.2.3 and 1.2.4-alpha.1 can't). This matches the behaviour of semver.

To change this behaviour you can use the flag --includePrerelease. This will treat all pre-release versionas as if they were normal versions (^1.2.3 and 1.2.4-alpha.1 can be deduplicated).

Usage in CI

This tool can be used as part of a CI workflow. Adding the flag --fail will force the process to exit with status 1 if there are duplicated packages. Example:

# Print the list of duplicated packages and exit with status 1 
yarn-deduplicate --list --fail
# Deduplicate yarn.lock and exit with status 1 if changes were required 
yarn-deduplicate --fail

Migration guide

From 2.x to 3.x

In this version we have adopted variadic arguments from commander.js. These are the equivalent commands:

yarn-deduplicate --packages libA,libB
yarn-deduplicate --scopes @scopeA,@scopeB
yarn-deduplicate --exclude libA,libB
yarn-deduplicate --packages libA libB
yarn-deduplicate --scopes @scopeA @scopeB
yarn-deduplicate --exclude libA libB

A consequence of this change is that if you were using one or more of the affected options ( --packages, --scopes or --exclude) and a custom path for yarn.lock, you need to use -- to "stop" package/scope/exclude parsing:

yarn-deduplicate --packages libA libB -- path/to/yarn.lock

From 0.x to 1.x

In this version we have renamed the project and refactored the CLI. These are the equivalent commands:


# Old 
npm install -g yarn-tools
# New 
npm install -g yarn-deduplicate

List duplicates

# Old 
yarn-tools list-duplicates path/to/yarn.lock
# New 
yarn-deduplicate --list path/to/yarn.lock

Deduplicate yarn.lock

# Old 
yarn-tools fix-duplicates path/to/yarn.lock > tmp
mv tmp path/to/yarn.lock
# New 
yarn-deduplicate path/to/yarn.lock

Limit packages to deduplicate yarn.lock

# Old 
yarn-tools fix-duplicates path/to/yarn.lock package1 package2
# New 
yarn-deduplicate --packages package1,package2 path/to/yarn.lock


Pull requests, issues and comments welcome. For pull requests:

  • Add tests for new features and bug fixes
  • Follow the existing style
  • Separate unrelated changes into multiple pull requests

See the existing issues for things to start contributing.

For bigger changes, make sure you start a discussion first by creating an issue and explaining the intended change.

Atlassian requires contributors to sign a Contributor License Agreement, known as a CLA. This serves as a record stating that the contributor is entitled to contribute the code/documentation/translation to the project and is willing to have it used in distributions and derivative works (or is willing to transfer ownership).

Prior to accepting your contributions we ask that you please follow the appropriate link below to digitally sign the CLA. The Corporate CLA is for those who are contributing as a member of an organization and the individual CLA is for those contributing as an individual.


Copyright (c) 2017 Atlassian and others. Apache 2.0 licensed, see LICENSE.txt file.


npm i yarn-deduplicate

DownloadsWeekly Downloads






Unpacked Size

58.5 kB

Total Files


Last publish


  • avatar