All you need is YAML.

gemspec.yml allows you to define all of your gem's metadata in plain YAML, and have it loaded by a boilerplate <name>.gemspec file which fills in any missing data with smart defaults.

git clone https://github.com/postmodern/gemspec.yml.git
mkdir newgem/
cp gemspec.yml/gemspec.yml newgem/
cp gemspec.yml/foo.gemspec newgem/newgem.gemspec

name: foo
summary: Foo gem
description:
  More stuff about the foo gem.

license: MIT
authors: You
email: you@example.com
homepage: https://github.com/you/foo#readme

metadata:
  documentation_uri: https://rubydoc.info/gems/foo
  source_code_uri:   https://github.com/postmodern/foo
  bug_tracker_uri:   https://github.com/postmodern/foo/issues
  changelog_uri:     https://github.com/postmodern/foo/blob/main/CHANGELOG.md

dependencies:
  bar: ~> 0.1
  baz: ~> 0.2, >= 0.2.4
  quix: ">= 1.2.3, < 2"

development_dependencies:
  bundler: ~> 2.0

post_install_message: |
  Multi-Line
  
      $ echo "post install"
  
  Message

$ gem build foo.gemspec
  Successfully built RubyGem
  Name: foo
  Version: 0.0.1
  File: foo-0.0.1.gem

• The file MUST be named gemspec.yml.
• The file MUST be located in the top-level directory of the gem.
• The file MUST contain plain YAML.
• Nested YAML elements MUST be indented by two spaces.
• Each line SHOULD NOT exceed 80 columns.
• The gemspec.yml file MUST be accompanied by a <name>.gemspec file, which loads it's contents.

The name of the gem.

name: foo

Required: yes

Type: String

Format: gem name

The version of the gem.

version: 0.1.0

Type: String

Format: version number

Required: no

Default: if omitted, the boilerplate gemspec will attempt to load the lib/<name>/version.rb file and resolve the <Name>::VERSION constant.

A short summary for the gem.

summary: Foo gem for all of you foo needs

Required: yes

Type: String

Format: text, single-line

A longer description for the gem.

description: Foo gem provides foo functionality for tasks requiring foo

description: |
  Foo gem for providing foo functionality.

  Please refer to the foo documentation.

Required: yes

Type: String

Format: text, multi-line

The license identifier for the gem.

license: MIT

license:
  - GPL-3.0
  - LGPL-3.0

Required: yes

Type: String or Array of Strings

Format: License identifier

The author(s) of the gem.

authors: Me

authors:
  - Me
  - Bob
  - Alice

Required: yes

Type: String or Array of Strings

Format: name

The primary email contact for the gem.

email: me@example.com

Required: yes

Type: String

Format: email address

The primary homepage for the gem.

homepage: https://foo.github.io/

Required: yes

Type: String

Format: URL

Additional metadata for the gem.

metadata:
  documentation_uri: https://rubydoc.info/gems/foo
  source_code_uri:   https://github.com/you/foo
  bug_tracker_uri:   https://github.com/you/foo/issues
  changelog_uri:     https://github.com/you/foo/blob/main/CHANGELOG.md

Required: no

Type: Hash of String => String

Format: identifier => text

The directories within the gem that will be added to $LOAD_PATH when the gem is loaded.

require_paths: lib

require_paths:
  - lib
  - vendor/*/lib

Type: String or Array of Strings

Format: relative path or dir glob pattern

Required: no

Default: if omitted, it will include the lib/ and ext/ directories, if they exist.

The executable file names that will be installed by the gem.

executables:
  - foo
  - bar

Type: Array of Strings

Format: file name

Required: no

Default: if omitted, it will default to the file names within the gem's bin/ directory.

Any extension build files that will be executed when the gem is installed.

extensions: ext/foo/extconf.rb

extensions: ext/*/{extconf.rb,Makefile}

Required: no

Default: if omitted, it will default to all extconf.rb files within the gem's ext/ directory, if it exists.

Type: String or Array of Strings

Format: relative path or dir glob pattern

The files that will be packaged into the gem.

files:
  - README.md
  - lib/**/*.rb

Required: no

Default: if omitted, it will use the output of git ls-files.

Type: String or Array of Strings

Format: relative path or dir glob pattern

Any additional files that should be included in auto-generated documentation.

extra_doc_files: *.md

extra_doc_files:
  - *.md
  - doc/EXAMPLES.md
  - doc/SPEC.txt

Required: no

Default: if omitted, it will include any top-level .txt or .md files.

Type: String or Array of Strings

Format: relative path or dir glob pattern

The unit/spec test files.

test_files: test/{**/}*_test.rb

Required: no

Default: if omitted, it will default to the {test/{**/}*_test.rb,spec/{**/}*_spec.rb glob pattern.

Type: String or Array of Strings

Format: relative path or dir glob pattern

Any external dependencies for the gem.

requirements: graphviz >= 2.0.0

requirements:
  - graphviz >= 2.0.0
  - sqlite3 >= 3.30.0

Required: no

Type: String or Array of Strings

Format: dependency

The Ruby version required to use this gem.

required_ruby_version: ">= 2.0.0"

Required: no

Type: String

Format: version requirement

Note: Strings beginning with > must be double-quoted for YAML.

The RubyGems version required to install or use this gem.

required_rubygems_version: ">= 3.0.0"

Required: no

Type: String

Format: version requirement

Note: Strings beginning with > must be double-quoted for YAML.

An optional message to display after the gem has been successfully installed.

post_install_message: |
  Congratulations on installing the Foo gem. Do not forget to edit ~/.foorc

Required: no

Type: String

Format: multi-line

Runtime gem dependencies for the gem.

dependencies:
  bar: ~> 0.1
  baz: ~> 0.5, < 2
  quix: ">= 1.2.3, < 2"

Required: no

Type: Hash of String => String

Format: gem name => version requirement

Note: Strings beginning with > must be double-quoted for YAML.

Development dependencies for the gem.

dependencies:
  bundler: ~> 2.0
  rspec: ~> 3.0

Required: no

Type: Hash of String => String

Format: gem name => version requirement

Note: Strings beginning with > must be double-quoted for YAML.