igmarin/rails-agent-skills

Curated library of 42 public AI agent skills for Ruby on Rails development, plus 5 callable workflow skills. Organized by category: planning, testing, code-quality, ddd, engines, infrastructure, api, patterns, context, orchestration, and workflows. Covers code review, architecture, security, testing (RSpec), engines, service objects, DDD patterns, and TDD automation.

Quality

96%

Does it follow best practices?

Impact

—

No eval scenarios have been run

Securityby

Risky

Do not use without reviewing

name:: create-engine-installer
license:: MIT
description:: Use when creating install generators, copied migrations, or initializer installers for Rails engines. Covers idempotent setup tasks, host-app onboarding, and route mount setup. Trigger words: install generator, mountable engine setup, gem installation, engine onboarding, rails plugin installer, copy migrations, initializer generator, route mount setup, engine configuration generator.
metadata:: {"version":"1.0.0","user-invocable":"true"}

Create Engine Installer

Name: igmarin/rails-agent-skills
Rating: 96.81553398058252 (1 reviews)
Author: igmarin

Use this skill when the task is to design or review how a host app installs and configures a Rails engine — generating initializers, copying migrations, mounting routes, or exposing a single install command.

Core principle: Setup must be explicit, repeatable, and safe to rerun. Never modify the host app at boot time.

Installer Components

Component	Purpose	Key constraint
Generator	Creates initializer, route mount, or setup files	Must be idempotent — safe to rerun
Migrations	Copies engine migrations into host `db/migrate`	Host owns and runs them; never apply automatically
Initializer	Provides configuration defaults	Generated once, editable by host
Routes	Adds `mount Engine, at: '/path'`	Check for existing mount before injecting

HARD-GATE: Validation Workflow

WHEN building or reviewing an install generator:

1. GENERATE:  Run the generator against a clean host app
2. VERIFY:    Check output files exist in the correct host paths
3. RERUN:     Run the generator a second time
4. CONFIRM:   No duplicate files, routes, or initializer blocks inserted
5. DOCUMENT:  List what was generated vs. what the user must do manually
6. TEST:      Cover both single-run and rerun behavior in generator specs

DO NOT ship a generator without completing steps 3 and 4.

Constraints

Constraint	Do	Avoid
Boot-time mutation	Configure only in initializers	Modifying host files or state at load time from `engine.rb` or initializers
Idempotency	Guard with `File.exist?` or Thor's `inject_into_file` with a marker	Overwriting or inserting routes, initializers, or migrations without checking
Migrations	Copy to host `db/migrate`; host runs them	Applying migrations automatically
Manual steps	Document rollback steps and required env vars	Leaving install gaps undocumented
Docs accuracy	Match install docs to generator behavior	Docs that describe a different install path than the generator produces

Idempotency guards — check before creating or injecting:

def create_initializer
  return if File.exist?(File.join(destination_root, 'config/initializers/my_engine.rb'))
  create_file 'config/initializers/my_engine.rb', <<~RUBY
    MyEngine.configure do |config|
      config.user_class = "User"
    end
  RUBY
end

def mount_route
  # inject_into_file with force: false skips insertion if sentinel already present
  inject_into_file 'config/routes.rb',
    "\n  mount MyEngine::Engine, at: '/admin'\n",
    after: "Rails.application.routes.draw do",
    force: false
end

Minimal rerun spec (must always pass):

it 'does not duplicate the route mount on rerun' do
  2.times { run_generator }
  expect(File.read(file('config/routes.rb')).scan('mount MyEngine::Engine').size).to eq(1)
end

See EXAMPLES.md for a full generator class and complete spec suite, including migration copy helpers and multi-step install scenarios.

Generator Checklist

Files created in correct host paths
No duplicate inserts on rerun (validated manually and in specs)
Sensible defaults that are easy to edit
Clear output telling the user what remains manual
Rollback steps documented
Install docs match what the generator actually produces

Integration

Skill	When to chain
create-engine	When designing the engine structure that installers will configure
document-engine	When documenting install steps or upgrade instructions
test-engine	When adding generator specs or dummy-app install coverage

Assets

assets/README.md

build

mcp_server

skills

api

context

ddd

infrastructure

orchestration

patterns

planning

testing

workflows

README.md

tile.json