What license does libtorrent use and what does it require of my project?

Updated

libtorrent is released under the BSD license. You can use the library in your own project without releasing your source code; the only requirement is that you credit the author by including the libtorrent license in your software or documentation. Contributing improvements back to the project is appreciated but not required.

What the BSD license allows

The project's own description of its terms is short and permissive:

  • Commercial and closed-source use is permitted. The site states explicitly that you can use the library in your project "without having to release its source code."
  • No copyleft obligation. Unlike licenses that require derivative works to be open-sourced, the BSD terms here impose no such requirement.
  • Modification is not restricted by the stated terms. The site does not attach conditions to modified versions beyond the credit requirement described below.

What your project must do

There is exactly one stated requirement: give credit to the author of the library by including the libtorrent license in your software or documentation.

In practice, that means placing the license text somewhere a user or reviewer can find it — for example:

  • a LICENSES/ or third_party/ directory in your source tree,
  • an open-source notices or credits screen in a desktop or mobile application,
  • an acknowledgements section in your product documentation.

The site does not prescribe a specific location or format, so the choice of where to put the notice is yours; the condition is that the license is included and the author credited.

What is optional

The project says it is "greatly appreciated if additional features are contributed back to the open source project," and notes that patches can be emailed to the mailing list or posted to the bug tracker. This is a request, not a license condition — nothing in the stated terms obliges you to publish changes.

Practical checklist before shipping

  1. Confirm you are using an official libtorrent release and keep a copy of the license text that shipped with it.
  2. Add the license to your distribution — source tree, notices file, or in-product credits.
  3. If you modify the library and want to share fixes, send a patch to the mailing list or file it on the bug tracker; if you prefer not to, no action is needed under the license.

Where to verify

The license statement appears on the libtorrent project site (libtorrent.org) alongside the introduction, which also describes the library as a feature-complete C++ BitTorrent implementation focused on CPU efficiency, memory efficiency, and ease of use. For the authoritative wording, read the license text distributed with the version you are using rather than relying on summaries.