yarn add: Add Dependencies

By Kaveh Alemi·Latchkey

yarn add installs a package and writes it to package.json.

yarn add is a developer command; CI normally only installs from the committed lockfile.

Common flags

-D / --dev - devDependency
-E / --exact - pin exact version
-P / --peer - peerDependency
yarn add <pkg>@<tag>

Example

Add a dev tool pinned exactly.

shell

yarn add -D -E vitest

In CI

If CI runs yarn add, it will change the lockfile and break --immutable. Keep dependency changes in PRs, not the build.

Using this in CI

Node tooling on a runner differs from your machine in three ways that matter: CI=true is set, there is no TTY, and the Node major may not be the one you develop on.

Pin the Node major with setup-node and in engines. Native modules resolve different prebuilt binaries per major.
CI=true changes behaviour in several tools, most often by promoting warnings to errors or disabling interactive prompts.
Commands that expect a TTY will hang. Pass the non-interactive or --yes flag explicitly.
Use npm exec or node_modules/.bin rather than assuming a globally installed binary is on PATH.

Key takeaways

-D for dev, -E to pin exact.
CI should not run yarn add.
Lockfile changes belong in PRs.

Frequently asked questions

yarn add: Add Dependencies?

yarn add is a developer command; CI normally only installs from the committed lockfile.

Example?

Add a dev tool pinned exactly.

In CI?

If CI runs yarn add, it will change the lockfile and break --immutable. Keep dependency changes in PRs, not the build.