Nitro Kit

Audience: Rails developers evaluating or installing Nitro Kit.

Nitro Kit is a gem-owned Phlex UI system for Rails. The 2.0.0.beta.3 prerelease is under active testing and is not stable.

Pin the prerelease:

gem "nitro_kit", "2.0.0.beta.3"

bundle install
bin/rails generate nitro_kit:install
bin/rails nitro_kit:doctor

Commit Gemfile and Gemfile.lock. Before upgrading, review the changelog, run bundle update nitro_kit, rerun the installer, and test the application. Production applications should use a released gem with a committed lockfile.

Start with:

• Rails integration
• Component contracts
• Customization
• Eject a component into application-owned code
• Browser support
• Nitro Kit 1.x migration
• Coding-agent guide

Nitro Kit targets maintained evergreen browsers from roughly the previous two years, with Mobile Safari as a first-class target. See the browser support policy for exact fallback behavior.

Add this to a product bootstrap prompt so the agent installs Nitro Kit, uses its guidance, and discovers optional product patterns when available:

Add Nitro Kit 2 to this Rails app and use it for the product's application UI.

Set up Nitro Kit before planning or implementing the product:
- Add and pin the current Nitro Kit 2 prerelease in the Gemfile, run bundle install, run bin/rails generate nitro_kit:install, and run bin/rails nitro_kit:doctor.
- Load the generated project-local Nitro Kit skills and installed, version-matched docs.
- Check whether Nitro Kit catalog or MCP tools are available. If they are, inventory and search them by product workflow, retrieve relevant patterns, and state what you will use, adapt, or defer.
- If no catalog is available, continue with the bundled docs and component contracts; catalog access is optional.

Maintaining Nitro Kit 1? Its frozen documentation remains at v1.nitrokit.dev.

Prefer tokens and composition. When you need to change a component's source:

bin/rails generate nitro_kit:eject Button

Render Ui::EjectedButton::Button.new("Save") and load ejected_button.css after nitro_kit.css. Ruby, CSS, and Stimulus dependencies become application-owned; keep the gem installed for the shared kernel and tokens. See Eject for integration, collision handling, and upgrade responsibilities.

Nitro Kit uses the custom NitroKit License.