What is libtorrent.org and what does the libtorrent library do?

libtorrent is a feature-complete BitTorrent protocol implementation written as a C++ library. It is designed for efficiency and scalability, runs on embedded devices as well as desktops, and ships with a simple BitTorrent client that demonstrates how to use the library. It fits projects that need BitTorrent functionality embedded in a C++ application rather than a standalone client, and it is released under the BSD license, so you can use it in your project without releasing your source code as long as you include the libtorrent license in your software or documentation.

What the library actually provides

The project describes itself as a "feature complete C++ bittorrent implementation" with three stated main goals:

• CPU efficiency — keep processing overhead low.
• Memory efficiency — keep the footprint small enough for constrained hardware.
• Ease of use — a well-documented library interface intended to be straightforward to integrate.

Because it targets both embedded devices and desktops, the same library can serve a small appliance and a full desktop application. The bundled simple client is the practical starting point: it shows the library in use rather than only describing the API.

Where to start

The site organizes its material around a few entry points:

If you are evaluating the library, read the tutorial first and then check the upgrade guide for the version you plan to use — the existence of separate 2.1, 2.0, and 1.2 upgrade pages means API changes between major versions are documented and worth reviewing before you commit to a version.

Beyond the core protocol

The project lists a set of extensions and bindings that matter if your requirements go past basic torrent transfer:

• Transport and discovery: uTP extensions, DHT extensions (including DHT security and DHT store extensions), UDP tracker protocol, HTTP seed, and multi-tracker support.
• Streaming: a streaming extension and libtorrent plugins.
• Language bindings: Python, Java, Go, and Node, for teams that do not want to work in C++ directly.

For example, if you need a Python service that downloads and seeds torrents, the Python bindings are the relevant entry point; if you need to serve media while downloading, look at the streaming material.

License and support

libtorrent is BSD-licensed. The only requirement stated is that you credit the author by including the libtorrent license in your software or documentation; contributing features back is appreciated but not required. Patches can go to the mailing list or the bug tracker.

Support channels are the mailing list (with an archive) for general discussion, the bug tracker on GitHub for defects, and IRC. The site also notes a 2020 security audit, which is useful context if security review is part of your evaluation.

When it is a good fit — and when it is not

Choose libtorrent if you are building a C++ application (or using one of the available bindings) that needs a complete BitTorrent implementation and you care about CPU and memory cost on hardware ranging from embedded to desktop. The BSD license also makes it viable for closed-source products.

Look elsewhere if you want a ready-made end-user BitTorrent client rather than a library to integrate — the included client is described as simple and is there to demonstrate library use, not to compete as a full application. Also check the upgrade guides against your target version before starting, since the documented 1.2, 2.0, and 2.1 transitions indicate interface changes across releases.