37signals Rails

37signals Rails Best Practices

Comprehensive coding principles and conventions for Ruby on Rails applications, as practiced at 37signals (Basecamp, HEY, Fizzy). Contains 56 rules across 8 categories, prioritized by architectural impact. Derived from official 37signals sources: the Fizzy codebase, STYLE.md, AGENTS.md, the Rails Doctrine, DHH's "On Writing Software Well" series, and the unofficial 37signals style guide (265 Fizzy PRs).

When to Apply

Reference these guidelines when:

• Writing new Rails controllers, models, or views
• Deciding between gems and vanilla Rails
• Modeling state and database schema
• Setting up background jobs, caching, or real-time features
• Reviewing code for 37signals-style conventions
• Refactoring toward rich domain models
• Choosing authentication or authorization approach
• Adding Stimulus controllers or Turbo patterns

Rule Categories by Priority

Quick Reference

1. Architecture Fundamentals (CRITICAL)

• arch-rich-models - Rich Domain Models Over Service Objects
• arch-vanilla-rails - Vanilla Rails is Plenty
• arch-avoid-patterns - Deliberately Avoided Patterns and Gems
• arch-earn-abstractions - Earn Abstractions Through Rule of Three
• arch-build-before-gems - Build It Yourself Before Reaching for Gems
• arch-ship-to-learn - Start Simple — Add Complexity Only After Validation
• arch-domain-facades - Domain Models as Facades Over Internal Complexity
• arch-single-business-layer - Single Layer for Business Logic
• arch-custom-auth - Custom Passwordless Auth Over Devise

2. Controllers & REST (CRITICAL)

• ctrl-crud-only - CRUD Controllers Over Custom Actions
• ctrl-model-as-resources - Model Non-CRUD Operations as Separate Resources
• ctrl-thin-controllers - Thin Controllers with Rich Domain Models
• ctrl-params-expect - Use params.expect() for Parameter Validation
• ctrl-controller-concerns - Controller Concerns for Cross-Cutting Behavior
• ctrl-nested-resources - Nested Resources with scope module

3. Domain Modeling (HIGH)

• model-concerns - Concerns for Horizontal Code Sharing
• model-normalizes - Use normalizes Macro for Data Cleaning
• model-store-accessor - Use store_accessor for JSON Column Access
• model-delegated-type - Use delegated_type for Polymorphism
• model-counter-caches - Counter Caches to Prevent N+1 Count Queries
• model-touch-chains - Touch Chains for Cache Invalidation
• model-callbacks-auxiliary - Callbacks for Auxiliary Complexity
• model-event-tracking - Polymorphic Event Model for Activity Tracking
• model-poro-namespacing - Namespace POROs Under Parent Models

4. State Management (HIGH)

• state-records-over-booleans - Records as State Over Boolean Columns
• state-timestamps - Timestamps for State Transitions
• state-enums - Enums for Categorical States
• state-db-constraints - Database Constraints Over ActiveRecord Validations
• state-write-time - Compute at Write Time Not Read Time

5. Database & Infrastructure (HIGH)

• db-backed-everything - Database-Backed Everything
• db-solid-queue - Solid Queue for Background Jobs
• db-solid-cable - Solid Cable for Real-Time Pub/Sub
• db-solid-cache - Solid Cache for Application Caching
• db-multi-tenancy - Path-Based Multi-Tenancy with Current.account
• db-uuid-primary-keys - UUIDs as Primary Keys
• db-no-foreign-keys - No Foreign Key Constraints

6. Views & Frontend (MEDIUM)

• view-turbo-frames - Turbo Frames for Scoped Page Fragments
• view-turbo-streams - Turbo Streams for Real-Time Updates
• view-stimulus-targets - Stimulus Targets Over CSS Selectors
• view-stimulus-design - Stimulus Controller Design Principles
• view-helpers-not-partials - Extract Logic to Helpers Not Partials
• view-progressive-enhancement - Progressive Enhancement as Primary Pattern
• view-fragment-caching - Fragment Caching for View Performance
• view-http-caching - HTTP Caching with fresh_when and ETags

7. Code Style (MEDIUM)

• style-conditionals - Expanded Conditionals Over Guard Clauses
• style-method-ordering - Methods Ordered by Call Sequence
• style-positive-names - Use Positive Names for Methods and Scopes
• style-naming-return-values - Method Names Reflect Return Values
• style-visibility-modifiers - Visibility Modifier Formatting
• style-bang-methods - Bang Methods Only When Non-Bang Exists
• style-async-naming - Use _later and _now Suffixes for Async Operations

8. Testing (MEDIUM)

• test-minitest - Minitest Over RSpec
• test-fixtures - Database Fixtures Over FactoryBot
• test-no-damage - No Test-Induced Design Damage
• test-no-system-tests - Integration Tests Over System Tests
• test-behavior - Test Behavior Not Implementation

How to Use

Read individual reference files for detailed explanations and code examples:

• Section definitions - Category structure and impact levels
• Rule template - Template for adding new rules

Reference Files

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