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ABOUT File Specification v3.2.1


An ABOUT file provides a simple way to document the provenance (origin and license) and other important or interesting information about a software component. An ABOUT file is a small YAML formatted text file stored in the codebase side-by-side with the software component file or archive that it documents. No modification of the documented software is needed.

The ABOUT format is plain text with field name/value pairs separated by a colon. It is easy to read and create by hand and is designed first for humans, rather than machines. The format is well-defined and structured just enough to make it easy to process with software as well. It contains enough information to fulfill key license requirements such as creating credits or attribution notices, collecting redistributable source code, or providing information about new versions of a software component.

Getting Started

A simple and valid ABOUT file named httpd-2.4.3.tar.gz.ABOUT may look like this:

about_resource: httpd-2.4.3.tar.gz
name: Apache HTTP Server
version: 2.4.3
license_expression: apache-2.0
    -   key: apache-2.0
        name: Apache License 2.0
        file: apache-2.0.LICENSE
notice_file: httpd.NOTICE
copyright: Copyright (c) 2012 The Apache Software Foundation.

The meaning of this ABOUT file is:

  • The file "httpd-2.4.3.tar.gz" is stored in the same directory and side-by-side with the ABOUT file "httpd-2.4.3.tar.gz.ABOUT" that documents it.
  • The name of this component is "Apache HTTP Server" with version "2.4.3".
  • The home URL for this component is
  • The file "httpd-2.4.3.tar.gz" was originally downloaded from
  • In the same directory, "apache-2.0.LICENSE" and "httpd.NOTICE" are files that contain respectively the license text and the notice text for this component.
  • This component is licensed under "apache-2.0"


An ABOUT file is an ASCII YAML formatted text file. Note that while Unicode characters are not supported in an ABOUT file proper, external files can contain UTF-8 Unicode. The key for the licenses field and the license_expression are dejacode license key.

ABOUT file name

An ABOUT file name can use a limited set of characters and is suffixed with a ".ABOUT" extension using any combination of uppercase and lowercase characters.

A file name can contain only these US-ASCII characters:

  • digits from 0 to 9
  • uppercase and lowercase letters from A to Z
  • the following symbols: "_", "-", "+", ".", "(", ")", "~", "[", "]", "{", "}", "@"
  • The case of a file name is not significant. On case-sensitive file systems (such as on Linux), a tool must report an error if two ABOUT files stored in the same directory have the same lowercase file name. This is to ensure that ABOUT files can be used across file systems. The convention is to use a lowercase file name and an uppercase ABOUT extension.

Lines of text

An ABOUT file contains lines of US-ASCII text. Lines contain field names/values pairs. The standard line ending is the LF character. The line ending characters can be any LF, CR or CR/LF and tools must normalize line endings to LF when processing an ABOUT file. Empty lines and lines containing only white spaces that are not part of a field value continuation are ignored. Empty lines are commonly used to improve the readability of an ABOUT file.

Field name

A field name can contain only these US-ASCII characters:

  • digits from 0 to 9
  • uppercase and lowercase letters from A to Z
  • the "_" underscore sign.
  • Field names are not case sensitive. For example, "HOMEPAGE_URL" and "HomePage_url" represent the same field name.
  • A field name must start at the beginning of a new line. No spaces is allowed in the field name. It can be followed by one or more spaces that must be ignored. These spaces are commonly used to improve the readability of an ABOUT file.

Field value

The field value is separated from the field name by a ":" colon. The ":" colon can be followed by one or more spaces that must be ignored. This also applies to trailing white spaces: they must be ignored.

The field value is composed of one or more lines of plain US-ASCII printable text.

When a field value is a long string, additional continuation lines must start with at least one space. In this case, the first space of an additional continuation line is ignored and should be removed from the field value by tools.

For instance:

description: This is a long description for a
 software component that additional continuation line is used.

When a field value contains more than one line of text, a 'literal block' (using |) is need.

For instance:

description: |
    This is a long description for a software component that spans
    multiple lines with arbitrary line breaks.

    This text contains multiple lines.

Fields are mandatory, optional or custom extension

A field can be mandatory, optional or custom extension. Tools must report an error for missing mandatory fields.

Fields validation

When processing an ABOUT file, tools must report a warning or error if a field is invalid. A field can be invalid for several reasons, such as invalid field name syntax or invalid content. Tools should report additional validation error details. The validation process should check that each field name is syntactically correct and that fields contain correct values according to its concise, common sense definition in this specification. For certain fields, additional and specific validations are relevant such as URL validation, path resolution and verification, and so forth. Tools should report a warning for present fields that do not have any value.

Fields order and multiple occurrences

The field order does not matter. Multiple occurrences of a field name is not supported.

The tool processing an ABOUT file or CSV/JSON input will issue an error when a field name occurs more than once in the input file.

Field referencing a file

The actual value of some fields may be contained in another file. This is useful for long texts or to reference a common text in multiple ABOUT files such as a common license text. In this case the field name is suffixed with "_file" and the field value must be a path pointing to the file that contains the actual value of the field. This path must be a POSIX path relative to the path of the ABOUT file. The file content must be UTF-8-encoded text. This is in contrast with field values contained directly in an ABOUT file that must be US-ASCII- encoded text and allows to support non-ASCII text content.

For example, the full license text for a component is often stored in a separate file named COPYING:

    -   file: linux.COPYING

In this example, the README file is stored in a doc directory, one directory above the ABOUT file directory, using a relative POSIX path:

    -   file: ../docs/ruby.README

In addition, there may be cases that a license can have 2 or more referenced license files. If this is the case, a comma ',' is used to identify multiple files For instance:

license_expression: gpl-2.0-plus
    -   key: gpl-2.0-plus

Field referencing a URL

The value of a field may reference URLs such as a homepage or a download. In this case the field name is suffixed with "_url" and the field value must be a valid absolute URL starting with ftp://, http:// or https://. URLs are informational and the content they may reference is ignored. For example, a download URL is referenced this way:


Flag fields

Flag fields have a "true" or "false" value. True, T, Yes, Y or x must be interpreted as "true" in any case combination. False, F, No or N must be interpreted as "false" in any case combination.

Referencing the file or directory documented by an ABOUT file

An ABOUT file documents one file or directory. The mandatory "about_resource" field reference the documented file or directory. The value of the "about_resource" field is the name or path of the referenced file or directory.

A tool processing an ABOUT file must report an error if this field is missing.

By convention, an ABOUT file is often stored in the same directory side-by-side to the file or directory that it documents, but this is not mandatory.

For example, a file named django.ABOUT contains the following field to document the django-1.2.3.tar.gz archive stored in the same directory:

about_resource: django-1.2.3.tar.gz

In this example, the ABOUT file documents a whole sub-directory:

about_resource: linux-kernel-2.6.23

In this example, the ABOUT file documents the current directory, using a "." period to reference it:

about_resource: .

Other Mandatory fields

When a tool processes an ABOUT file, it must issue an error if these mandatory field are missing.

  • about_resource: The resource this file referencing to.
  • name: Component name.

Optional Information fields

  • version: Component or package version. A component or package usually has a version, such as a revision number or hash from a version control system (for a snapshot checked out from VCS such as Subversion or Git). If not available, the version should be the date the component was provisioned, in an ISO date format such as 'YYYY-MM-DD'.
  • spec_version: The version of the ABOUT file format specification used for this file. This is provided as a hint to readers and tools in order to support future versions of this specification.
  • description: Component description, as a short text.
  • download_url: A direct URL to download the original file or archive documented by this ABOUT file.
  • homepage_url: URL to the homepage for this component.
  • changelog_file: Changelog file for the component.
  • package_url: Package URL for the package.
  • notes: Notes and comments about the component.

Optional Owner and Author fields

  • owner: The name of the primary organization or person(s) that owns or provides the component.
  • owner_url: URL to the homepage for the owner.
  • contact: Contact information (such as an email address or physical address) for the component owner.
  • author: Name of the organization(s) or person(s) that authored the component.
  • author_file: Author file for the component.

Optional Licensing fields

  • copyright: Copyright statement for the component.
  • notice_file: Legal notice or credits for the component.
  • notice_url: URL to a legal notice for the component.
  • license_file: License file that applies to the component. For example, the name of a license file such as LICENSE or COPYING file extracted from a downloaded archive.
  • license_url: URL to the license text for the component.
  • license_expression: The DejaCode license expression that apply to the component. You can separate each identifier using " or " and " and " to document the relationship between multiple license identifiers, such as a choice among multiple licenses (No special characters are allowed).
  • license_name: The DejaCode license short name for the license (No special characters are allowed).
  • license_key: The DejaCode license key(s) for the component (No special characters are allowed).

Optional Boolean flag fields

  • redistribute: Set this flag to yes if the component license requires source code redistribution. Defaults to no when absent.
  • attribute: Set this flag to yes if the component license requires publishing an attribution or credit notice. Defaults to no when absent.
  • track_changes: Set this flag to yes if the component license requires tracking changes made to a the component. Defaults to no when absent.
  • modified: Set this flag to yes if the component has been modified. Defaults to no when absent.
  • internal_use_only: Set this flag to yes if the component is used internal only. Defaults to no when absent.

Optional Extension fields

You can create extension fields by prefixing them with a short prefix to distinguish these from the standard fields (but this is not necessary).

Optional Extension fields to reference files stored in a version control system (VCS)

These fields provide a simple way to reference files stored in a version control system. There are many VCS tools such as CVS, Subversion, Git, ClearCase and GNU Arch. Accurate addressing of a file or directory revision in each tool in a uniform way may not be possible. Some tools may require access control via user/password or certificate and this information should not be stored in an ABOUT file. This extension defines the 'vcs' field extension prefix and a few common fields to handle the diversity of ways that VCS tools reference files and directories under version control:

  • vcs_tool: VCS tool such as git, svn, cvs, etc.
  • vcs_repository: Typically a URL or some other identifier used by a VCS tool to point to a repository such as an SVN or Git repository URL.
  • vcs_path: Path used by a particular VCS tool to point to a file, directory or module inside a repository.
  • vcs_tag: tag name or path used by a particular VCS tool.
  • vcs_branch: branch name or path used by a particular VCS tool.
  • vcs_revision: revision identifier such as a revision hash or version number.

Some examples for using the vcs_* extension fields include:

vcs_tool: svn
vcs_path: trunk/inkscape_planet/
vcs_revision: 22886


vcs_tool: git
vcs_repository: git://
vcs_path: tools/lib/traceevent
vcs_revision: b59958d90b3e75a3b66cd311661535f94f5be4d1

Optional Extension fields for checksums

These fields support checksums (such as SHA1 and MD5)commonly provided with downloaded archives to verify their integrity. A tool can optionally use these to verify the integrity of a file documented by an ABOUT file.

  • checksum_md5: MD5 for the file documented by this ABOUT file in the "about_resource" field.
  • checksum_sha1: SHA1 for the file documented by this ABOUT file in the "about_resource" field.
  • checksum_sha256: SHA256 for the file documented by this ABOUT file in the "about_resource" field.

Some examples:

checksum_md5: f30b9c173b1f19cf42ffa44f78e4b96c
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