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

# 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:

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

Current Attributes:

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

Authorization on Models:

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>