What is the BSD license, and how is it used?

The BSD (Berkeley Software Distribution) license is a permissive open-source license that allows developers to use, modify, and distribute software with minimal restrictions. Unlike copyleft licenses like the GPL, the BSD license does not require derivative works to be open-source, making it a popular choice for both commercial and non-commercial projects. There are two primary variants: the 3-Clause BSD (or “New BSD”) and the 2-Clause BSD (“Simplified BSD”). The key requirements are retaining the original copyright notice, a disclaimer of warranty, and, in the 3-Clause version, a prohibition on using the project’s contributors’ names for endorsement without permission. This simplicity makes the BSD license easy to integrate into projects of all types.

Developers typically use the BSD license by including its text in the source code files of their project. For example, a project under the 3-Clause BSD would include a header like: “Copyright [year] [owner]. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted…” This ensures compliance when others reuse the code. The license is often chosen for libraries or tools intended to be integrated into proprietary software. FreeBSD, an open-source operating system, uses the 2-Clause BSD, allowing companies like Apple to incorporate its code into macOS without exposing proprietary components. Similarly, PostgreSQL uses a BSD-like license, enabling its use in commercial products without legal friction.

Compared to licenses like the MIT or GPL, the BSD license offers fewer constraints. The MIT license is similarly permissive but lacks the 3-Clause BSD’s endorsement restriction. The GPL, by contrast, mandates that derivative works remain open-source, which can deter commercial adoption. The BSD license is ideal for developers prioritizing flexibility, such as when building foundational tools (e.g., the React framework, which uses a BSD-like license) or infrastructure projects like nginx. Its permissiveness encourages broad adoption, making it a pragmatic choice for projects aiming to maximize reach while maintaining attribution.