API docs for Toolchain support.

When you call nodejs_register_toolchains() in your WORKSPACE file it will setup a node toolchain for executing tools on all currently supported platforms.

If you have an advanced use-case and want to use a version of node not supported by this repository, you can also register your own toolchains.

Node.js binary for the target platform

Sometimes your target platform (where your software runs) is different from the host platform (where you run Bazel) or execution platform (where Bazel actions run). The most common case is developing a docker image on MacOS, which will execute in a Linux container.

Our toolchain support is conditional on the execution platform, as it’s meant for running nodejs tools during the build. It is not needed for this use case. Instead, simply select the nodejs you want to include in the runtime.

For example, rules_docker has a nodejs_image rule, which takes a node_repository_name attribute indicating which nodejs binary you want to include in the image. nodejs_linux_amd64 is the value you’d use.


Bazel Toolchains are intended to support cross-compilation, e.g. building a linux binary from mac or windows. Most JavaScript use cases produce platform-independent code, but the exception is native modules which use node-gyp. Any native modules will still be fetched and built, by npm/yarn, for your host platform, so they will not work on the target platform. The workaround is to perform the npm_install inside a docker container so that it produces modules for the target platform.

Follow for updates on support for node-gyp cross-compilation.

Registering a custom toolchain

To run a custom toolchain (i.e., to run a node binary not supported by the built-in toolchains), you’ll need four things:

1) A rule which can build or load a node binary from your repository (a checked-in binary or a build using a relevant rules_foreign_cc build rule will do nicely). 2) A node_toolchain rule which depends on your binary defined in step 1 as its target_tool. 3) A toolchain rule that depends on your node_toolchain rule defined in step 2 as its toolchain and on @rules_nodejs//nodejs:toolchain_type as its toolchain_type. Make sure to define appropriate platform restrictions as described in the documentation for the toolchain rule. 4) A call to the register_toolchains function in your WORKSPACE that refers to the toolchain rule defined in step 3.

Examples of steps 2-4 can be found in the documentation for node_toolchain.

If necessary, you can substitute building the node binary as part of the build with using a locally installed version by skipping step 1 and replacing step 2 with:

2) A node_toolchain rule which has the path of the system binary as its target_tool_path



cypress_toolchain(name, cypress_bin, cypress_bin_path, cypress_files)

Defines a cypress toolchain.

For usage see



(Name, mandatory): A unique name for this target.


(Label): A hermetically downloaded cypress executable binary for the target platform.

Defaults to None


(String): Path to an existing cypress executable for the target platform.

Defaults to ""


(Label): A hermetically downloaded cypress filegroup of all cypress binary files for the target platform. Must be set when cypress_bin is set.

Defaults to None



configure_esbuild_toolchains(name, platforms)

Configures esbuild toolchains for a list of supported platforms




Defaults to ""


dict of platforms to configure toolchains for

Defaults to {}



cypress_repositories(name, version, linux_urls, linux_sha256, darwin_urls, darwin_sha256,
                     darwin_arm64_urls, darwin_arm64_sha256, windows_urls, windows_sha256)
Repository rule used to install cypress binary.



Name of the external workspace where the cypress binary lives


Version of cypress binary to use. Should match package.json


(Optional) URLs at which the cypress binary for linux distros of linux can be downloaded. If omitted, will be used.

Defaults to []


(Optional) SHA-256 of the linux cypress binary

Defaults to ""


(Optional) URLs at which the cypress binary for darwin can be downloaded. If omitted, will be used.

Defaults to []


(Optional) SHA-256 of the darwin cypress binary

Defaults to ""


(Optional) URLs at which the cypress binary for darwin arm64 can be downloaded. If omitted, will be used (note: as of this writing (11/2021), Cypress does not have native arm64 builds, and this URL will link to the x86_64 build to run under Rosetta).

Defaults to []


(Optional) SHA-256 of the darwin arm64 cypress binary

Defaults to ""


(Optional) URLs at which the cypress binary for windows distros of linux can be downloaded. If omitted, will be used.

Defaults to []


(Optional) SHA-256 of the windows cypress binary

Defaults to ""



esbuild_repositories(npm_repository, name, npm_args, kwargs)

Helper for fetching and setting up the esbuild versions and toolchains

This uses Bazel’s downloader (via http_archive) to fetch the esbuild package from npm, separately from any npm_install/yarn_install in your WORKSPACE. To configure where the download is from, you make a file containing a rewrite rule like

rewrite (*)$1/$2

You can find some documentation on the rewrite patterns in the Bazel sources:

Then use the --experimental_downloader_config Bazel option to point to your file. For example if you created .bazel_downloader_config you might add to your .bazelrc file:

common --experimental_downloader_config=.bazel_downloader_config



the name of the repository where the @bazel/esbuild package is installed by npm_install or yarn_install.


currently unused

Defaults to ""


additional args to pass to the npm install rule

Defaults to []


additional named parameters to the npm_install rule