Yarn is a fast, reliable and secure dependency manager. It caches packages so they’re only downloaded once; verifies each one before executing any code; and installs dependencies in a deterministic manner, so if in an install works on one system it will work on another.
Yarn caches every package it downloads so it never needs to again. It also parallelizes operations to maximize resource utilization so install times are faster than ever.
Yarn uses checksums to verify the integrity of every installed package before its code is executed.
Using a detailed, but concise, lockfile format, and a deterministic algorithm for installs, Yarn is able to guarantee that an install that worked on one system will work exactly the same way on any other system.