Specification for META.yml

## Specification for the META.yml file

This document describes version 1.0 of the META.yml specification.

The META.yml file describes important properties of contributed Perl distributions such as the ones found on CPAN. It is typically created by tools like Module::Build and ExtUtils::MakeMaker.

The fields in the META.yml file are meant to be helpful to people maintaining module collections (like CPAN), for people writing installation tools (like CPAN.pm or CPANPLUS), or just people who want to know some stuff about a distribution before downloading it and starting to install it.

### Format

META.yml files are written in the YAML format. The reasons we chose YAML instead of, say, XML or Data::Dumper are discussed in this thread on the MakeMaker mailing list.

The first line of a META.yml file should be a valid YAML document header like `"--- #YAML:1.0"`.

### Fields

The rest of the META.yml file is one big YAML mapping, whose keys are described here.

- name
  Example: Module-Build

  The name of the distribution. Often created by taking the "main module" in the distribution and changing "::" to "-". Sometimes it's completely different, however, as in the case of the libwww-perl distribution.

- version
  Example: 0.16

  The version of the distribution to which the META.yml file refers. This is a mandatory field.

  The version is essentially an arbitrary string, but must be only ASCII characters, and strongly should be of the format integer-dot-digit-digit, i.e. `25.57`, optionally followed by underscore-digit-digit, i.e. `25.57_04`.

  The standard tools that deal with module distribution (PAUSE, CPAN, etc.) form an identifier for each distribution by joining the 'name' and 'version' attributes with a dash (`-`) character. Tools who are prepared to deal with distributions that have no version numbers generally omit the dash as well.

- license
  Example: perl

  a descriptive term for the licenses ... not authoritative, but must be consistent with licensure statements in the READMEs, documentation, etc.

  The license under which this distribution may be used and redistributed. See Module::Build for the list of valid options.

- license_uri

  This should contain a URI where the exact terms of the license may be found.

  (change "unrestricted" to "redistributable"?)
- distribution_type
  Example: module

  What kind of stuff is contained in this distribution. Most things on CPAN are `module`s (which can also mean a collection of modules), but some things are `script`s.

  This field is basically meaningless, and tools (like Module::Build or MakeMaker) will likely stop generating it in the future.
- private
  WTF is going on here? index_ignore: any application that indexes the contents of distributions (PAUSE, search.cpan.org) ought to ignore the items (packages, files, directories, namespace hierarchies).
- requires
  Example:
  Data::Dumper: 0
  File::Find: 1.03

  A YAML mapping indicating the Perl modules this distribution requires for proper operation. The keys are the module names, and the values are version specifications as described in the documentation for Module::Build's "requires" parameter.

  Note: the exact nature of the fancy specifications like `">= 1.2, != 1.5, < 2.0"` is subject to change. Advance notice will be given here. The simple specifications like `"1.2"` will not change in format.

- recommends
  Example:
  Data::Dumper: 0
  File::Find: 1.03

  A YAML mapping indicating the Perl modules this distribution recommends for enhanced operation.

- build_requires
  Example:
  Data::Dumper: 0
  File::Find: 1.03

  A YAML mapping indicating the Perl modules required for building and/or testing of this distribution. These dependencies are not required after the module is installed.

- conflicts
  Example:
  Data::Dumper: 0
  File::Find: 1.03

  A YAML mapping indicating the Perl modules that cannot be installed while this distribution is installed. This is a pretty uncommon situation.

  - possibly separate out test-time prereqs, complications include: can tests be meaningfully preserved for later running? are test-time prereqs in addition to build-time, or exclusive? - make official location for installed *distributions*, which can contain tests, etc.
- dynamic_config
  Example: 0

  A boolean flag indicating whether a `Build.PL` or `Makefile.PL` (or similar) must be executed, or whether this module can be built, tested and installed solely from consulting its metadata file. The main reason to set this to a true value if that your module performs some dynamic configuration (asking questions, sensing the environment, etc.) as part of its build/install process.

  Currently `Module::Build` doesn't actually do anything with this flag - it's probably going to be up to higher-level tools like `CPAN.pm` to do something useful with it. It can potentially bring lots of security, packaging, and convenience improvements.

- generated_by
  Example: Module::Build version 0.16

  Indicates the tool that was used to create this META.yml file. It's good form to include both the name of the tool and its version, but this field is essentially opaque, at least for the moment.

  * Ingy's suggestions short_description: (add as field, containing abstract, maximum 80 characters, suggested minimum 40 characters) description: (long version of abstract, should add?) maturity: alpha, beta, gamma, mature, stable author_id, owner_id: categorization, keyword, chapter_id: URL for further information: (could default to search.cpan.org on PAUSE) namespaces: can be specified for single elements by prepending dotted-form, i.e. "com.example.my_application.my_property". Default namespace for META.yml is probably "org.cpan.meta_author" or something. Precedent for this is Apple's Carbon namespaces, I think.

### History

- March 14, 2003 (Pi day) - created version 1.0 of this document.
- May 8, 2003 - added the "dynamic_config" field, which was missing from the initial version.