Jr Rails New

Rails App Scaffolder

Interactive skill that interviews you for preferences, runs rails new with the right flags, and performs post-scaffold configuration.

Workflow

Step 0: Preflight

Quick check that the machine can actually run rails new. Skip the install prompts if everything is present.

command -v ruby   >/dev/null 2>&1 && ruby --version
command -v node   >/dev/null 2>&1 && node --version
command -v bundle >/dev/null 2>&1 && bundle --version
command -v mise   >/dev/null 2>&1 && mise --version

Required:

• Ruby 4.0 or newer (parse ruby --version; reject 3.x and older).
• Node 20 or newer.
• bundle available (ships with Ruby).
• mise (or rbenv / asdf) so the Ruby/Node we just probed survives a shell restart and matches .tool-versions later.

If anything's missing or out of date, surface the gap and offer to hand off:

This Mac isn't quite ready for `rails new` yet:
  ✗ Ruby is <version> (need 4.0+)
  ✗ Node not found
  ✓ mise installed

I can run /jr-rails-bootstrap to fix that - it installs the missing pieces
in the right order, then comes back here. Or you can install them manually
and re-run me.

Want me to launch /jr-rails-bootstrap?

Use AskUserQuestion with options Yes, run bootstrap, No, I'll install manually, Continue anyway (rails new may fail). If they pick bootstrap, invoke /jr-rails-bootstrap and stop - bootstrap will return them here via Phase E.

If everything passes, print one line per tool with version and continue.

Step 1: Interview

Ask the user each question. Show the default in brackets. Accept the default if the user presses enter or says "default" / "yes" / "y".

Testing is always Minitest — non-negotiable for jr-rails skills.

Step 2: Generate

Build and run the rails new command:

rails new APP_NAME \
  --database=DATABASE \
  --css=CSS \
  --skip-test=false \
  --devcontainer  # if dev container = yes

Bundling flags:

• importmap → no extra flag (default)
• esbuild → --javascript=esbuild
• vite_rails → no flag; add vite_rails gem post-scaffold

CSS flags:

• tailwind → --css=tailwind
• sass → --css=sass
• none → --skip-css

Step 3: Post-scaffold Configuration

Run these in order, skipping any that don't apply:

3a. Vite (if selected)

cd APP_NAME
bundle add vite_rails
bundle exec vite install

Remove importmap-rails from Gemfile if present.

3b. Phlex (if selected)

bundle add phlex-rails

Then create the base classes from reference/coding-phlex.md:

• app/components/base.rb — Components::Base < Phlex::HTML
• app/views/base.rb — Views::Base < Components::Base
• app/components/layout.rb — Components::Layout with Phlex::Rails::Layout

Set the layout in ApplicationController:

layout -> { Components::Layout }

Remove the ERB layout file (app/views/layouts/application.html.erb).

Install the custom scaffold generator from reference/coding-phlex.md § Scaffolding so future rails g scaffold produces Phlex views.

3c. Authentication

Rails built-in (8+):

rails g authentication

Devise:

bundle add devise
rails g devise:install
rails g devise User

3d. Pundit (if selected)

bundle add pundit
rails g pundit:install

Add to ApplicationController:

class ApplicationController < ActionController::Base
  include Pundit::Authorization
  after_action :verify_authorized, except: :index
  after_action :verify_policy_scoped, only: :index
end

3e. Sidekiq (if selected instead of Solid Queue)

bundle add sidekiq

Configure in config/application.rb:

config.active_job.queue_adapter = :sidekiq

3f. CLAUDE.md

Create CLAUDE.md in the app root with project conventions. The How to start section is load-bearing: /jr-rails-bootstrap and future agents read it to know how to launch the dev server. Derive its command from the actual stack choices (Q#3 bundling, Q#6 devcontainer, Q#10 worktree).

# Project Conventions

## Stack
- Ruby on Rails [version]
- [Database]
- [CSS framework]
- [View layer]
- Minitest with fixtures

## How to start

[Pick ONE block based on the stack choices made in the interview:]

### Default (no devcontainer, no worktree)
\`\`\`bash
bin/dev
\`\`\`
App: http://localhost:3000

### Vite (Q#3 = vite_rails) without devcontainer
\`\`\`bash
bin/dev   # foreman runs Rails + Vite together via Procfile.dev
\`\`\`
App: http://localhost:3000
Vite dev server: http://localhost:5173

### Devcontainer (Q#6 = yes)
\`\`\`bash
devcontainer up --workspace-folder .
devcontainer exec --workspace-folder . bin/dev
\`\`\`
App: http://localhost:3000

### Worktree workflow (Q#10 = yes)
Use the wt-managed binstub - port and database are derived per branch.
\`\`\`bash
wt start             # equivalent to: bin/agent-server
\`\`\`
App URL: see \`wt list\` for the branch's port (e.g. http://localhost:30421).

## Testing
- Run tests: `bin/rails test`
- Run system tests: `bin/rails test:system`

## Style
- Follow 37signals/classic Rails conventions
- Rich domain models, CRUD controllers, concerns
- No service objects - use domain models in app/models/
- Minitest with fixtures (no RSpec, no factory_bot)
- Database constraints over model validations for hard guarantees

## Skills
- `/jr-rails-classic` - coding style guide
[- `/jr-rails-phlex` - Phlex components (if Phlex selected)]
- `/jr-rails-review` - code review

Pick exactly one "How to start" block based on the interview answers and write that block (not the multi-choice template) into the project CLAUDE.md. The skill should resolve the right command at scaffold time, not punt the choice to a future reader.

3g. Worktree config (if selected)

Set up the agentic worktree workflow using worktrunk. The exact binstubs and database.yml depend on the database choice (Q#2) and whether dev containers are enabled (Q#6).

1. Create .config/wt.toml (same for all strategies):

[list]
url = "http://localhost:{{ branch | hash_port }}"

[post-create]
setup = "AGENT_WORKSPACE={{ branch | sanitize }} AGENT_ROOT_PATH={{ primary_worktree_path }} bin/agent-setup"

[pre-remove]
cleanup = "AGENT_WORKSPACE={{ branch | sanitize }} bin/agent-cleanup"

[post-remove]
kill-server = "lsof -ti :{{ branch | hash_port }} -sTCP:LISTEN | xargs kill 2>/dev/null || true"

[post-start]
server = "PORT={{ branch | hash_port }} VITE_RUBY_PORT={{ (branch ~ '-vite') | hash_port }} bin/agent-server"

2. Create the binstubs from reference/agentic-worktrees.md, choosing the variant that matches the stack:

The per-worktree devcontainer strategy uses devcontainer up / devcontainer exec (not raw docker compose) so that features, containerEnv, and postCreateCommand from devcontainer.json are applied. The postCreateCommand should be bin/setup --skip-server.

The shared PG strategy is simpler: one PostgreSQL container shared across all worktrees, Rails runs on the host. Prefer this when the host already has Ruby (via mise/rbenv/asdf) and you want worktrees to run tests independently.

3. Modify config/database.yml to use workspace-aware names:

• SQLite: prefix each database path with AGENT_WORKSPACE (defaults to development). See reference § config/database.yml (SQLite).
• PostgreSQL: suffix database name with AGENT_WORKSPACE. See reference § config/database.yml (PostgreSQL).

4. If dev container = yes, create .devcontainer/agent.json extending the main devcontainer with AGENT_* env vars forwarded into the container.

5. Update CLAUDE.md with worktree workflow docs (see reference § CLAUDE.md).

6. Update README.md with the workflow (see reference § Project README).

7. Create .claude/settings.json:

{
  "permissions": {
    "allow": [
      "Bash(git worktree *)",
      "Bash(git branch *)",
      "Bash(wt *)",
      "Bash(bin/agent-*)",
      "Bash(docker compose *)",
      "Bash(devcontainer *)"
    ]
  }
}

See reference/agentic-worktrees.md for full templates, port allocation scheme, and configuration details.

3h. Verify & Commit

bin/setup
bin/rails test  # should pass with zero tests

Create initial commit:

git add -A
git commit -m "Initial Rails app with [stack summary]"

Step 4: Summary

Print a summary of what was configured. Derive the "Next steps" command from the same logic as the CLAUDE.md "How to start" block - they must match.

✅ Rails app created: APP_NAME
   Database:       postgresql
   CSS:            tailwind
   View layer:     erb
   Authentication: rails (built-in)
   Authorization:  pundit
   Background:     solid_queue
   Dev container:  yes
   Worktree:       no
   Testing:        minitest (always)

Next steps:
  cd APP_NAME
  <START_COMMAND>

Where <START_COMMAND> matches the chosen stack:

Then add the app URL on the next line:

App:  http://localhost:3000   # or the worktree-specific port

Reference

• Classic coding style: reference/coding-classic.md
• Phlex coding style: reference/coding-phlex.md
• DevOps & deployment: reference/devops.md
• Gem recommendations: reference/toolbelt.md