It depends.
Both GNU Lesser GPL v2.1 and GNU Lesser GPL v3.0 are weak (file- or library-level) copyleft licenses. Combining them is usually feasible, but the obligations of each apply to its own files. Have a lawyer review if you intend to redistribute the combined work.
| License | Family | Patent grant |
|---|---|---|
| GNU Lesser GPL v2.1 (LGPL-2.1) | weak-copyleft | No (implicit at most) |
| GNU Lesser GPL v3.0 (LGPL-3.0) | weak-copyleft | Yes |
GNU Lesser GPL v2.1: Library copyleft: dynamic linking permitted from non-LGPL code without triggering full copyleft.
GNU Lesser GPL v3.0: Same library-linking permission as LGPL-2.1, with GPLv3's patent provisions inherited.
If you found this page because you're trying to figure out whether shipping a particular dependency is safe, the answer above is a starting point — not a substitute for reading the actual licenses or talking to a lawyer when stakes are high.
LicenseHound walks every transitive dependency in your repo, maps each to its SPDX license, and flags pairs like this one in PR comments. The CLI is free; the team dashboard is paid.