Licence Guidelines

Formulae in homebrew/core must use a licence compatible with the Debian Free Software Guidelines or be released into the public domain under the DFSG public-domain guidance.

Specifying a licence

Each licence is identified using an identifier from the SPDX License List.

Specify a licence by passing it to the license method:

license "MIT"

The public domain can be indicated using a symbol:

license :public_domain

If the licence for a formula cannot be represented using an SPDX expression:

license :cannot_represent

Complex SPDX licence expressions

Some formulae have multiple licences that need to be combined in different ways. In these cases, a more complex licence expression can be used. These expressions are based on the SPDX License Expression Guidelines.

Add a + to indicate that the user can choose a later version of the same licence:

license "EPL-1.0+"

GNU licences (GPL, LGPL, AGPL and GFDL) require either the -only or the -or-later suffix to indicate whether a later version of the licence is allowed:

license "LGPL-2.1-only"

license "GPL-1.0-or-later"

Use :any_of to indicate that the user can choose which licence applies:

license any_of: ["MIT", "0BSD"]

Use :all_of to indicate that the user must comply with multiple licences:

license all_of: ["MIT", "0BSD"]

Use :with to indicate a licence exception:

license "MIT" => { with: "LLVM-exception" }

These expressions can be nested as needed:

license any_of: [
  "MIT",
  :public_domain,
  { all_of: ["0BSD", "Zlib", "Artistic-1.0+"],
  "Apache-2.0" => { with: "LLVM-exception" } },
]

Specifying forbidden licences

The HOMEBREW_FORBIDDEN_LICENSES environment variable can be set to forbid installation of formulae that require or have dependencies that require certain licences.

HOMEBREW_FORBIDDEN_LICENSES should be set to a space-separated list of licences. Use public_domain to forbid installation of formulae with a :public_domain licence.

For example, the following forbids installation of MIT, Artistic-1.0 and :public_domain licences:

export HOMEBREW_FORBIDDEN_LICENSES="MIT Artistic-1.0 public_domain"

In this example Homebrew would refuse to install any formula that specifies the MIT licence. Homebrew would also forbid installation of any formula that declares a dependency on a formula that specifies MIT, even if the original formula has an allowed licence.

Homebrew interprets complex licence expressions and determines whether the licences permit installation. To continue the above example, Homebrew would not allow installation of a formula with the following licence declarations:

license any_of: ["MIT", "Artistic-1.0"]

license all_of: ["MIT", "0BSD"]

Homebrew would allow formulae with the following declaration to be installed:

license any_of: ["MIT", "0BSD"]

HOMEBREW_FORBIDDEN_LICENSES can also forbid future versions of specific licences. For example, to forbid Artistic-1.0, Artistic-2.0 and any future Artistic licences, use:

export HOMEBREW_FORBIDDEN_LICENSES="Artistic-1.0+"

For GNU licences (such as GPL, LGPL, AGPL and GFDL), use -only or -or-later. For example, the following would forbid GPL-2.0, LGPL-2.1 and LGPL-3.0 formulae from being installed, but would allow GPL-3.0:

export HOMEBREW_FORBIDDEN_LICENSES="GPL-2.0-only LGPL-2.1-or-later"