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.

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

What are you working on?

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

Specify a number or describe your task.

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

Domain Knowledge

All detailed patterns in references/:

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

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