Library is a broad tag for reusable code packages that solve a specific, well-defined problem rather than shipping a full application or framework. It spans utility libraries (Lodash for JavaScript, Requests for Python HTTP calls), data structure and algorithm implementations, parsing and serialization libraries, and small single-purpose packages that get pulled into larger projects as dependencies.
Because this tag covers such a wide range of functionality, evaluation criteria matter more than any single feature comparison. A library that does one thing well, has a small dependency footprint, and stays maintained tends to outlast a more feature-rich alternative that pulls in a large dependency tree. Checking a library's own dependencies before adding it is worth the time, since a single added package can quietly bring in dozens of transitive ones.
API stability is another practical concern. Libraries with a long history of backward-compatible releases are lower risk for production use than newer packages still iterating on their public interface, even if the newer package has more features on paper. Semantic versioning adherence, changelog quality, and how breaking changes are communicated are all reasonable signals to check in a library's release history before upgrading.
For anything handling untrusted input, such as parsing or serialization libraries, security advisory history is worth a quick look, since these libraries sit directly in the path of external data.
Things to compare between libraries solving the same problem: