davekilleen/dhh-rails-style

<objective> Apply 37signals/DHH Rails conventions to Ruby and Rails code. This skill provides comprehensive domain expertise extracted from analyzing production 37signals codebases (Fizzy/Campfire) and DHH's code review patterns. </objective>

<essential_principles>

Core Philosophy

"The best code is the code you don't write. The second best is the code that's obviously correct."

Vanilla Rails is plenty:

• Rich domain models over service objects
• CRUD controllers over custom actions
• Concerns for horizontal code sharing
• Records as state instead of boolean columns
• Database-backed everything (no Redis)
• Build solutions before reaching for gems

What they deliberately avoid:

• devise (custom ~150-line auth instead)
• pundit/cancancan (simple role checks in models)
• sidekiq (Solid Queue uses database)
• redis (database for everything)
• view_component (partials work fine)
• GraphQL (REST with Turbo sufficient)
• factory_bot (fixtures are simpler)
• rspec (Minitest ships with Rails)
• Tailwind (native CSS with layers)

Development Philosophy:

• Ship, Validate, Refine - prototype-quality code to production to learn
• Fix root causes, not symptoms
• Write-time operations over read-time computations
• Database constraints over ActiveRecord validations

</essential_principles>

<intake> What are you working on?

1. Controllers - REST mapping, concerns, Turbo responses, API patterns
2. Models - Concerns, state records, callbacks, scopes, POROs
3. Views & Frontend - Turbo, Stimulus, CSS, partials
4. Architecture - Routing, multi-tenancy, authentication, jobs, caching
5. Testing - Minitest, fixtures, integration tests
6. Gems & Dependencies - What to use vs avoid
7. Code Review - Review code against DHH style
8. General Guidance - Philosophy and conventions

Specify a number or describe your task. </intake>

<routing>

| Response | Reference to Read | |----------|-------------------| | 1, controller | controllers.md | | 2, model | models.md | | 3, view, frontend, turbo, stimulus, css | frontend.md | | 4, architecture, routing, auth, job, cache | architecture.md | | 5, test, testing, minitest, fixture | testing.md | | 6, gem, dependency, library | gems.md | | 7, review | Read all references, then review code | | 8, general task | Read relevant references based on context |

After reading relevant references, apply patterns to the user's code. </routing>

<quick_reference>

Naming Conventions

Verbs: card.close, card.gild, board.publish (not set_style methods)

Predicates: card.closed?, card.golden? (derived from presence of related record)

Concerns: Adjectives describing capability (Closeable, Publishable, Watchable)

Controllers: Nouns matching resources (Cards::ClosuresController)

Scopes:

• chronologically, reverse_chronologically, alphabetically, latest
• preloaded (standard eager loading name)
• indexed_by, sorted_by (parameterized)
• active, unassigned (business terms, not SQL-ish)

REST Mapping

Instead of custom actions, create new resources:

POST /cards/:id/close    → POST /cards/:id/closure
DELETE /cards/:id/close  → DELETE /cards/:id/closure
POST /cards/:id/archive  → POST /cards/:id/archival

Ruby Syntax Preferences

ruby
# Symbol arrays with spaces inside brackets
before_action :set_message, only: %i[ show edit update destroy ]

# Private method indentation
  private
    def set_message
      @message = Message.find(params[:id])
    end

# Expression-less case for conditionals
case
when params[:before].present?
  messages.page_before(params[:before])
else
  messages.last_page
end

# Bang methods for fail-fast
@message = Message.create!(params)

# Ternaries for simple conditionals
@room.direct? ? @room.users : @message.mentionees

Key Patterns

State as Records:

ruby
Card.joins(:closure)         # closed cards
Card.where.missing(:closure) # open cards

Current Attributes:

ruby
belongs_to :creator, default: -> { Current.user }

Authorization on Models:

ruby
class User < ApplicationRecord
  def can_administer?(message)
    message.creator == self || admin?
  end
end

</quick_reference>

<reference_index>

Domain Knowledge

All detailed patterns in references/:

| File | Topics | |------|--------| | controllers.md | REST mapping, concerns, Turbo responses, API patterns, HTTP caching | | models.md | Concerns, state records, callbacks, scopes, POROs, authorization, broadcasting | | frontend.md | Turbo Streams, Stimulus controllers, CSS layers, OKLCH colors, partials | | architecture.md | Routing, authentication, jobs, Current attributes, caching, database patterns | | testing.md | Minitest, fixtures, unit/integration/system tests, testing patterns | | gems.md | What they use vs avoid, decision framework, Gemfile examples | </reference_index>

<success_criteria> Code follows DHH style when:

• Controllers map to CRUD verbs on resources
• Models use concerns for horizontal behavior
• State is tracked via records, not booleans
• No unnecessary service objects or abstractions
• Database-backed solutions preferred over external services
• Tests use Minitest with fixtures
• Turbo/Stimulus for interactivity (no heavy JS frameworks)
• Native CSS with modern features (layers, OKLCH, nesting)
• Authorization logic lives on User model
• Jobs are shallow wrappers calling model methods

</success_criteria>

<credits> Based on The Unofficial 37signals/DHH Rails Style Guide by Marc Köhlbrugge, generated through deep analysis of 265 pull requests from the Fizzy codebase.

Important Disclaimers:

• LLM-generated guide - may contain inaccuracies
• Code examples from Fizzy are licensed under the O'Saasy License
• Not affiliated with or endorsed by 37signals

</credits>