:fox_face: Foxtail :globe_with_meridians:

A Ruby implementation of Project Fluent with two gems:

• foxtail-runtime: runtime bundle parsing + message formatting
• foxtail-tools: CLI + full syntax parser/serializer

Gems

foxtail-runtime

Runtime formatting with ICU4X integration and fluent.js-compatible bundle parsing.

foxtail-tools

Tooling for authoring and validating FTL files (CLI + full syntax parser/serializer).

Installation

Add the gems you need to your application's Gemfile:

gem "foxtail-runtime"
# Optional tooling (CLI + syntax parser)
gem "foxtail-tools"

Then install:

$ bundle install

Require entry points based on what you use:

require "foxtail-runtime" # Runtime APIs
require "foxtail-tools"   # CLI + tooling APIs

Quick Start (runtime)

require "foxtail-runtime"
require "icu4x"

resource = Foxtail::Resource.from_string(<<~FTL)
  hello = Hello, { $name }!
  emails =
      You have { $count ->
          [one] one email
         *[other] { $count } emails
      }.
FTL

bundle = Foxtail::Bundle.new(ICU4X::Locale.parse("en-US"))
bundle.add_resource(resource)

bundle.format("hello", name: "Alice")
# => "Hello, Alice!"

bundle.format("emails", count: 1)
# => "You have one email."

bundle.format("emails", count: 5)
# => "You have 5 emails."

CLI (tools)

foxtail check messages.ftl
foxtail dump messages.ftl
foxtail ids messages.ftl
foxtail tidy messages.ftl

See foxtail-tools/doc/cli.md for full CLI reference.

Development

After checking out the repo, run:

$ bin/setup

This installs dependencies, configures ICU4X data, and initializes the fluent.js submodule.

Running Tests

# All tests
$ bundle exec rake spec

# Per gem
$ bundle exec rake spec:runtime
$ bundle exec rake spec:tools

Code Quality

$ bundle exec rake rubocop

Architecture

Foxtail is split into two gems with distinct responsibilities:

• foxtail-runtime: Runtime components (bundle parsing, message formatting, ICU4X integration)
• foxtail-tools: Tooling components (syntax parser/serializer and CLI)

Architecture notes per gem:

• Runtime Architecture
• Tools Architecture

Related docs:

• Parser System - FTL syntax parsing and AST implementation
• Bundle System - Runtime message formatting with icu4x integration
• Sequence - Language fallback chains
• Language Negotiation - Accept-Language handling and safe fallback guidelines

Compatibility

• Ruby: 3.2 or higher
• fluent.js: 159/160 test fixtures passing (99.4%)
  • Syntax parser: 97/98 (99.0%)
  • Bundle parser: 62/62 (100%)

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/sakuro/foxtail.

1. Fork it
2. Create your feature branch (git checkout -b feature/add-some-feature)
3. Run the tests (bundle exec rake spec)
4. Commit your changes (git commit -am ':sparkles: Add some feature')
5. Push to the branch (git push origin feature/add-some-feature)
6. Create new Pull Request

Acknowledgments

This project stands on the shoulders of giants:

• ICU4X: Number, date/time, plural rules, and locale handling
• Fluent Project: Foxtail aims for compatibility with Mozilla's Fluent localization system, particularly fluent.js (Apache 2.0)

License

The gem is available as open source under the terms of the MIT License.