Yarn and npm are both package managers for JavaScript, but there are some key differences between them:

1. Speed: Yarn is generally faster than npm, especially when it comes to installing dependencies.

2. Offline Mode: Yarn has an offline mode that allows you to install packages without an internet connection. npm does not have this feature.

3. Deterministic: Yarn guarantees deterministic installs, which means that given a set of dependencies, Yarn will always install the same versions of those dependencies. npm does not have this guarantee.

4. Security: Yarn has a built-in mechanism for verifying the integrity of packages that are downloaded. npm relies on the npm registry to ensure the integrity of packages.

5. Concurrent Installations: Yarn can install packages concurrently, which can be faster than npm's sequential installation process.

6. Workspaces: Yarn has a feature called workspaces that allows you to manage multiple packages in a single codebase. npm does not have this feature.

Overall, both Yarn and npm are widely used and reliable package managers for JavaScript. The choice between them largely depends on personal preference and project requirements