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How to apply the Apache 2.0 License to your Open Source software project

Written on 02 October 2021

Apache 2.0 License is one of the best OSS licenses to use in your Open Source software project, but do you actually know how to properly apply it? We'll go through all the common mistakes and show how to use the license correctly.

I’ve always been a 3-Clause BSD License (AKA New BSD License or Modified BSD License) guy. As I’ve matured, my understanding of Open Source licensing has grown as well, and so have my requirements. When I start a new Open Source project now, I just use Apache 2.0 license. I want to point out that I am not a lawyer, and I am certainly not your lawyer. My legal opinions are based on research and lengthy conversations with legal departments of companies that I worked for.

Why Apache 2.0 license?

There are various reasons why I prefer Apache 2.0 license over the others (specifically the 3-Clause BSD License). This WhiteSource article covers the differences nicely, but for completeness, let me mentioned them here explicitly as well:

Explicit grant of patent rights: Apache License 2.0 explicitly lays down the grant of patent rights while using, modifying, or distributing Apache licensed software; it also lists the circumstances when such grant gets withdrawn.
Precise definitions of the used concepts: Apache License 2.0 explicitly defines all the terms and concepts that it uses. This leaves little scope for ambiguity.
Reusable without rewording: Apache License 2.0 can be easily used by other projects without any rewording in the license document itself. It also means that it should be sufficient to provide the canonical URL https://www.apache.org/licenses/LICENSE-2.0.txt, where the copy of the license can be obtained, instead of the license text.

These differences are most important to me, but other differences like “prominent notices stating that You changed the files” might be more critical for you. Here is the full text of the Apache 2.0 license:

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                                Apache License
                           Version 2.0, January 2004
                        http://www.apache.org/licenses/

TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION

1. Definitions.

   "License" shall mean the terms and conditions for use, reproduction,
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END OF TERMS AND CONDITIONS

APPENDIX: How to apply the Apache License to your work.

      To apply the Apache License to your work, attach the following
      boilerplate notice, with the fields enclosed by brackets "[]"
      replaced with your own identifying information. (Don't include
      the brackets!)  The text should be enclosed in the appropriate
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Copyright [yyyy] [name of copyright owner]

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

There are two variants of the Apache 2.0 license: justified version and version with text aligned to the left. The justified version is the one you get by fetching https://www.apache.org/licenses/LICENSE-2.0.txt - I call it the canonical form. The license has 201 lines of text and is composed of the header (lines 1-3), the terms and conditions (lines 5-176) and the appendix (lines 178-201).

License

To apply the license to your software project, create a LICENSE file in the source tree’s top level. Now copy the full Apache 2.0 License text from https://www.apache.org/licenses/LICENSE-2.0.txt into a LICENSE file. Notice that the LICENSE file doesn’t have any extension, but you can optionally name the file LICENSE.txt as well.

Do not modify the license text. If you used a 3-Clause BSD License in the past, you usually downloaded the license template, changed it, and saved it as a LICENSE file.

Copyright <YEAR> <COPYRIGHT HOLDER>

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

You may be tempted to do the same with Apache 2.0 License. The license text contains what looks like a copyright notice on line 189:

Copyright [yyyy] [name of copyright owner]

Actually, this is a copyright notice template and an additional boilerplate that are part of the Apache 2.0 License appendix, which starts at line 178 and explains how to apply the Apache License to individual source files instead of having one single LICENSE file in the top level of the source tree. The text in the appendix is very explicit about what the copyright notice template and additional boilerplate are for (use in source files). Changing this copyright notice template directly in license text is IMHO an improper application of the license. The whole appendix (lines 178-201) can technically be omitted from the license, as it’s outside the scope of “Section 1 through 9”, which forms the terms and conditions of the license.

My opinion is backed by the “Reusable without rewording” attribute of the Apache 2.0 License I mentioned before. It’s even backed by my experience in a big corporation - two years ago, I was working for one of the biggest tech companies in the world. The company had established an Open Source office with a Legal Department dealing with use of Open Source within the company. This Open Source office stipulated that for an Open Source project to be licensed under Apache 2.0 License, it is not required to have an explicit Apache 2.0 License text as part of the project. It is absolutely sufficient if the Open Source project README file contains the name of the license, either “Apache 2.0 License” or its SPDX identifier. Ideally, (but not required) canonical URL where the copy of the license can be obtained should be mentioned as well: https://www.apache.org/licenses/LICENSE-2.0.txt. This is just a legal opinion of one big tech company. Don’t take this legal opinion as implied truth.

Copyright notice

In the previous section, we’ve stipulated that the Apache 2.0 License text doesn’t actually have a place where to put an explicit copyright notice. Since 1989, Berne Convention established that the copyright is automatic, and the use of copyright notices to claim the copyright has become optional.

This is how an explicit copyright notice looks like:

Copyright 2021 Vladimír Gorej <vladimir.gorej@gmail.com>

When an explicit copyright notice is missing in Open Source software that you want to use in your project, you’re theoretically still OK, as it is possible to compile one using the following assumptions:

The name of the copyright holder is the name of the first committer to the project
The copyright holder contact is established by using the email address of the first committer
The year of the copyright notice is established as the year of the first commit to the project

If you cannot somehow obtain the above information, you’re kind of screwed, as there is no way to establish the copyright notice for compliance purposes in big tech companies.

It’s always a good idea to provide an explicit copyright notice when applying the Apache 2.0 License. But, where do we put one? Well, if we would read the Apache 2.0 Licence terms and conditions carefully, section 4.d) (line 106) has an answer for that: a “NOTICE” text file. Just create a new file called NOTICE and put your copyright notice there.

Today there are three competing formats of copyright notices:

Historical format: Copyright 2017-2019, Vladimír Gorej
Copyright 1998, Linus Torvalds
Newer format: Copyright The Ramda Adjunct contributors
Copyright The Kubernetes Authors
Hybrid format: Copyright 2017-2019 Vladimír Gorej and the Ramda Adjunct contributors

Given above, your NOTICE file could look like this:

Ramda Adjunct
Copyright 2017, Vladimír Gorej

Closing words

Choose the appropriate Open Source license for the needs of your project. If you’re deciding between BSD, MIT, and Apache 2.0, go for Apache 2.0 License. The license automatically grants patent rights. It’s clear, explicit, and reusable without rewording. To apply the license to your Open Source software project, create two files: LICENSE and NOTICE in the top level of the source tree. The copy of the license text that you obtained from https://www.apache.org/licenses/LICENSE-2.0.txt goes into the LICENSE file. Your copyright notice goes into the NOTICE file. Doing these two things makes the application of the Apache 2.0 License as explicit and clear as it can be. Sounds pretty easy, right?

Another good source of information about applying Apache 2.0 License to a software project can be official “How to” from Apache Software Foundation directed to Apache Committers.