BSD Software License: Types, Terms, and How to Use It

The BSD software license is one of the oldest and most influential open source licenses in software development. First used by the University of California, Berkeley for its Berkeley Software Distribution (BSD) Unix variant in the late 1980s, the BSD license family has shaped how permissive licensing works across the entire open source ecosystem.

This article provides an educational overview of the BSD software license and its variants. It is not legal advice. Consult a qualified attorney for guidance on licensing decisions specific to your project or business.

What Is the BSD Software License?

The BSD software license is a permissive open source license that grants broad rights to use, copy, modify, and distribute software in both source code and binary forms. Unlike copyleft licenses such as the GPL, the BSD license does not require that derivative works be released under the same license. This makes it one of the most flexible licenses available.

The core terms of the BSD software license can be summarized in three points:

• You may use, modify, and redistribute the software freely.
• You must include the original copyright notice and license text in any redistribution.
• The software is provided "as is" without warranty of any kind.

The BSD license is approved by the Open Source Initiative (OSI) and is compatible with virtually every other open source license, making it a safe choice for libraries and components that need to be widely adopted.

BSD License Variants Explained

Over time, the original BSD license has evolved into several variants. Each addresses a specific concern while maintaining the same permissive foundation. Understanding the differences between these variants is essential when evaluating a BSD software license for your project.

Original BSD License (4-Clause)

The original BSD license, sometimes called the "old BSD license," contained four clauses. The most notable was the advertising clause, which required that all advertising materials mentioning the software include a specific credit to the University of California, Berkeley.

This clause became impractical as projects incorporated dozens or hundreds of BSD-licensed components, each requiring its own advertising acknowledgment. The advertising clause also created a compatibility conflict with the GNU General Public License (GPL), since the additional requirement was considered a restriction that the GPL does not permit.

The University of California officially dropped the advertising clause in 1999. The 4-Clause BSD license is rarely used today and is generally not recommended for new projects.

BSD 3-Clause License (New BSD / Modified BSD)

The BSD 3-Clause license removed the problematic advertising clause and is the most commonly referenced BSD software license in modern projects. Its three clauses are:

1. Redistribution of source code must retain the original copyright notice, the list of conditions, and the disclaimer.
2. Redistribution in binary form must reproduce the copyright notice, conditions, and disclaimer in the documentation or other materials provided with the distribution.
3. Non-endorsement: The names of the copyright holders and contributors may not be used to endorse or promote products derived from the software without specific prior written permission.

The 3-Clause BSD license is used by projects including FreeBSD, the Go programming language standard library, and many scientific computing tools. It is compatible with the GPL v2 and GPL v3.

BSD 2-Clause License (Simplified BSD / FreeBSD License)

The BSD 2-Clause license simplifies the 3-Clause version by removing the non-endorsement clause. It contains only:

1. Source redistribution must retain the copyright notice, conditions, and disclaimer.
2. Binary redistribution must reproduce the copyright notice, conditions, and disclaimer in the documentation.

This makes the BSD 2-Clause license functionally very similar to the MIT License. The FreeBSD project uses this variant, which is why it is sometimes called the "FreeBSD License." It is the simplest BSD variant and is a good choice when you want maximum permissiveness with minimal legal text.

BSD 0-Clause License (Zero-Clause BSD)

The BSD 0-Clause license (also called the Free Public License or 0BSD) goes a step further by removing all conditions. It is essentially a public domain dedication with a license fallback for jurisdictions that do not recognize public domain dedications.

The full text is remarkably short:

Permission to use, copy, modify, and distribute this software for any purpose with or without fee is hereby granted. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES.

The 0BSD license is useful for code samples, tutorials, and small utilities where even attribution requirements would be burdensome. It was approved by the OSI in 2006.

BSD Software License Terms and Conditions

Despite its brevity, the BSD software license contains several important legal provisions that users and distributors should understand.

Copyright Notice Requirement

Every BSD variant (except 0-Clause) requires that redistributions include the original copyright notice. This is the single most important compliance obligation. In practice, this means:

• Including a LICENSE or COPYING file in your source distributions
• Reproducing the copyright notice in binary distributions (often in an "About" dialog, NOTICE file, or documentation)
• Preserving the copyright notice in source code files when you fork or modify them

"As Is" Disclaimer

All BSD variants include a warranty disclaimer stating that the software is provided "as is" without any warranty, express or implied. This protects the original authors from liability for defects, damages, or fitness for a particular purpose. The disclaimer is typically rendered in uppercase for legal emphasis.

Non-Endorsement (3-Clause Only)

The third clause in the BSD 3-Clause license prevents users from implying that the original authors endorse their derivative products. This protects the reputation of the original developers and their institutions.

BSD Software License vs. Other Open Source Licenses

Understanding how the BSD software license compares to other popular licenses helps you make informed decisions about which license to adopt or accept.

BSD vs. MIT License

The MIT License and BSD 2-Clause License are functionally equivalent. Both are permissive, require attribution, and allow use in proprietary software. The key differences are:

• Language: MIT uses slightly different wording but grants the same permissions.
• Simplicity: MIT is a single paragraph. BSD 2-Clause separates conditions for source and binary redistribution.
• Ecosystem conventions: JavaScript and web development projects tend to favor MIT. Systems programming and scientific computing often use BSD.

For practical purposes, choosing between them is largely a matter of community convention rather than legal substance.

BSD vs. Apache 2.0

Apache 2.0 is also permissive but includes additional provisions:

• Explicit patent grant: Apache 2.0 includes a patent license, protecting users from patent claims by contributors. The BSD license has no patent provision.
• Change documentation: Apache 2.0 requires that modified files carry a notice stating they were changed. BSD has no such requirement.
• NOTICE file: Apache 2.0 requires a NOTICE file to be included in distributions.

If patent protection is a concern for your project, Apache 2.0 may be more appropriate than the BSD software license.

BSD vs. GPL

The GPL and BSD licenses represent fundamentally different philosophies:

• BSD prioritizes developer freedom. You can take BSD code, modify it, and release the result as proprietary software.
• GPL prioritizes user freedom. Any derivative work must be released under the GPL, ensuring end users always have access to the source code.

BSD-licensed code can be incorporated into GPL-licensed projects (since the GPL imposes additional restrictions, not fewer). However, GPL code cannot be incorporated into BSD-licensed projects without the entire project becoming GPL.

Using BSD-Licensed Software in Your Projects

Incorporating BSD-licensed code into your own software is straightforward, but compliance still matters. Here is a practical checklist:

1. Identify the specific BSD variant (2-Clause, 3-Clause, or 0-Clause). Read the actual license file in the repository rather than assuming based on the project description.
2. Copy the LICENSE file into your project's third-party notices or licenses directory.
3. Include the copyright notice in binary distributions. Common approaches include a "Third-Party Licenses" section in your documentation, an in-app credits screen, or a NOTICE file.
4. Respect the non-endorsement clause (3-Clause). Do not use the original author's name or organization to promote your derivative product without written permission.
5. Check for license compatibility if you are combining BSD code with code under other licenses. BSD is compatible with most licenses, but verify when mixing with AGPL or other restrictive licenses.

BSD License in Web Applications

When you build web applications using BSD-licensed libraries, those libraries may interact with user data. For example, a BSD-licensed HTTP library, form validator, or analytics component may process personal information submitted by your users.

Under the GDPR (Articles 13 and 14), the CCPA (California Civil Code Section 1798.100), and similar privacy laws, you are required to disclose what data your application collects and how it is processed, regardless of the license of the underlying code. A privacy policy generator can help you create a policy that accurately reflects the data practices of your application, including any data processed by third-party open source components.

Licensing Your Own Software Under the BSD License

If you are creating a new project and considering the BSD software license, here is what you need to decide and do:

Choosing a Variant

• Use BSD 2-Clause if you want maximum simplicity and do not care about endorsement restrictions.
• Use BSD 3-Clause if you want to prevent others from using your name to promote their derivative products.
• Use BSD 0-Clause if you want to maximize adoption and do not require any attribution at all.

Applying the License

1. Create a LICENSE file in the root of your repository containing the full license text with your copyright notice (year and name or organization).
2. Add an SPDX license identifier to your package.json, Cargo.toml, or equivalent manifest file (e.g., BSD-2-Clause, BSD-3-Clause, or 0BSD).
3. Optionally, add a license header to each source file. This is common practice in larger projects but not strictly required.

Considerations for Businesses

If your company is releasing software under the BSD license, consider these factors:

• Patent exposure: BSD does not include a patent grant. If your software implements patented technology, contributors and users have no automatic patent license. Consider Apache 2.0 if patent protection is important.
• Contributor agreements: For projects that accept external contributions, a Contributor License Agreement (CLA) or Developer Certificate of Origin (DCO) clarifies IP ownership.
• Dual licensing: Some companies offer their software under both a BSD license (for open source use) and a commercial license (for proprietary use with additional support or warranties).

If your business operates a website or application, you will also need legal documents such as a privacy policy, terms of service, and potentially a cookie policy. TermsBox provides automated compliance tools that generate and maintain these documents based on your actual site configuration.

BSD License in Practice: Notable Projects

The BSD software license has been adopted by some of the most important software projects in computing history:

• FreeBSD, OpenBSD, NetBSD: The BSD operating systems that directly descend from the original Berkeley Software Distribution.
• Nginx: One of the most widely deployed web servers, licensed under the BSD 2-Clause license.
• PostgreSQL: While it uses the "PostgreSQL License," it is functionally identical to BSD 2-Clause.
• Django: The Python web framework uses BSD 3-Clause.
• Flask: The Python microframework uses BSD 3-Clause.
• Go standard library: Uses BSD 3-Clause.

Apple's macOS and iOS are built on a foundation that includes significant BSD-licensed code from the Darwin/XNU kernel, which descends from FreeBSD and Mach. This demonstrates one of the defining characteristics of the BSD license: permissive terms allow even the largest commercial entities to build proprietary products on top of open source foundations.

Frequently Asked Questions

What is the BSD software license?

The BSD software license is a permissive open source license that allows users to use, modify, and redistribute software with minimal restrictions. It originated at the University of California, Berkeley in the 1980s and requires only that the original copyright notice and license text be included in redistributions.

What is the difference between the BSD 2-Clause and 3-Clause licenses?

The BSD 2-Clause license (Simplified BSD) requires attribution in source and binary redistributions. The BSD 3-Clause license (New BSD) adds a third clause prohibiting the use of the original author's name to endorse or promote derivative products without written permission. Both are permissive and allow commercial use.

Can I use BSD-licensed software in a commercial product?

Yes, the BSD software license explicitly permits commercial use. You can incorporate BSD-licensed code into proprietary products, modify it, and sell it. The only requirement is that you include the original copyright notice and license text in your distribution.

How does the BSD license differ from the GPL?

The BSD license is permissive, meaning derivative works can be released under any license, including proprietary ones. The GPL is a copyleft license that requires derivative works to also be released under the GPL. BSD gives developers maximum freedom in how they use the code, while GPL ensures all derivatives remain open source.