Convert yarn.lock to package-lock.json and vice versa

Usage no npm install needed!

<script type="module">
  import synp2 from '';


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Convert yarn.lock to package-lock.json and vice versa.


npm install -g synp

command line usage

yarn.lock => package-lock.json

yarn # be sure the node_modules folder dir and is updated
synp --source-file /path/to/yarn.lock
# will create /path/to/package-lock.json

package-lock.json => yarn.lock

npm install # be sure the node_modules dir exists and is updated
synp --source-file /path/to/package-lock.json
# will create /path/to/yarn.lock

Note: if all you need is to convert in this direction (package-lock.json => yarn.lock), as of 1.7.0, Yarn is able to import its dependency tree from npm’s package-lock.json natively, without external tools. Use the yarn import command.

programmatic usage

const { npmToYarn, yarnToNpm } = require('synp')

const libPath = '/path/to/my/lib'
const stringifiedYarnLock = npmToYarn(libPath)
const stringifiedPackageLock = yarnToNpm(libPath)

how does it work?

Since package-lock.json and yarn.lock use different methods in order to deterministically lock down dependency versions, oftentimes they do not contain all the information needed to be purely converted.

For this reason, synp uses the existing node_modules directory of the package to determine the package state and assist in the conversion.

For this reason, it is vital to make sure the node_modules directory of the package is current and was installed by the respective tool (eg. by yarn if converting to package-lock.json and by npm if converting to yarn.lock).


Bundled dependencies: For various reasons, this tool does not 'play well' with bundled dependencies. This should not be a problem because installing the packages later with the converted file will (by definition) update the proper packages in the file. If this is not the case for you, please open an issue/PR with your use case and I'd be happy to take a look.

Package checksums: Both yarn.lock and package-lock.json include package checksums for dependencies. Since npm is slowly moving to sha-512 checksums which yarn does not (yet) support, converting to package-lock.json will result in weaker checksums (that will still work!) and converting to yarn.lock can sometimes result in a corrupted result file. Thankfully, this issue is 100% solvable. In npm one can update the checksums simply by deleting the integrity field of all or relevant packages. In yarn this can be solved with the --update-checksums* flag when installing from the created file.

Format limitations: Some things that can be expressed in one format simply cannot be expressed in the other. These are (to the best of my knowledge) extreme edge cases and should not worry 99% of this tool's intended users. One example is package-lock.json's ability to translate the same semver string to different versions. (eg. one package requesting version ^1.0.1 of a dependency and receiving 1.0.5 and a different package requesting version ^1.0.1 of the same dependency and receiving 1.0.71. When translating to yarn.lock through synp both will receive the same version).

Optional packages: Like npm (, synp also has issues with optional dependencies across different platforms. This is because it uses node_modules as its state, and does not guess about packages that are not installed on the converting platform. Sadly, like npm the only way to avoid this issue is to perform the conversion on the platform that meets most optional dependencies and update the rest manually. If this is a major issue for you, adding some sort of automatic tooling for this can be discussed.

* At the time of this writing, the --update-checksums flag in yarn has been merged but not released yet. Please see:


  1. checksum mismatch when installing from converted file? In yarn use --update-checksums, in npm delete the integrity field from the offending package (have no fear! This will be updated upon installation).
  2. synp failing or not converting properly - remove the node_modules from the package to be converted, install it again (with yarn if converting to package-lock.json or npm if converting to yarn.lock) and run synp one more time.
  3. something else? - please open an issue/PR.