How to Add New License Rules for Enhanced Detection

ScanCode relies on license rules to detect licenses. A rule is a simple text file containing a license text or notice or mention with YAML frontmatter with data attributes that tells ScanCode which license expression to report when the text is detected, and other properties.

See the FAQ for a high level description of adding license detection rules.

How to add a new license detection rule?

A license detection rule is a file with:

  • a plain text that is typically a variant of a license text, notice or license mention.

  • data as YAML frontmatter documenting license expression and other rule attributes.

To add a new rule, you need to pick a unique base file name. As a convention, we like to include the license expression that should be detected in that name to make it more descriptive. For example: mit_and_gpl-2.0 is a good base name for a rule that would detect an MIT and GPL-2.0 license combination at once. Add a suffix (usually numeric) to make it unique if there is already a rule with this base name. Do not use spaces or special characters in that name.

Then create the rule file in the src/licensedcode/data/rules/ directory using this name; for example a rule with license_expression as mit AND apache-2.0 might have a filename: mit_and_apache-2.0_10.RULE.

Save your rule text in this file; if there are specific words like company names, projects or other, it is better to have rules with and without these so we have better detection.

For a simple mit AND apache-2.0 license expression detection, here is an example rule file:

license_expression: mit AND apache-2.0
is_license_notice: yes
relevance: 100

## License
The MIT License (MIT) + Apache 2.0. Read [LICENSE](LICENSE).

See the src/licensedcode/data/rules/ directory for many examples.

More (advanced) rules options:

  • you can use a notes text field to document this rule and explain where you found it first.

  • if no license should be detected for your .RULE text, do not add a license expression, just add a notes field.

  • Each rule needs to have one flag to describe the type of license rule. The options are:

    • is_license_notice

    • is_license_text

    • is_license_tag

    • is_license_reference

    • is_license_intro

  • There can also be false positive rules, which if detected in the file scanned, will not be present in the result license detections. These just have the license text and a is_false_positive flag set to True.

  • you can specify key phrases by surrounding one or more words between the {{ and }} tags. Key phrases are words that must be matched/present in order for a RULE to be considered a match.

See the src/licensedcode/ directory for a list of all possible values and other options.


Add rules in a local developement installation and run scancode-reindex-licenses to make sure we reindex the rules and this validates the new licenses.