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The Unofficial 37signals/DHH Rails Style Guide

About This Document

This style guide was generated by Claude Code through deep analysis of the Fizzy codebase - 37signals' open-source project management tool.

Why Fizzy matters: While 37signals has long advocated for "vanilla Rails" and opinionated software design, their production codebases (Basecamp, HEY, etc.) have historically been closed source. Fizzy changes that. For the first time, developers can study a real 37signals/DHH-style Rails application - not just blog posts and conference talks, but actual production code with all its patterns, trade-offs, and deliberate omissions.

How this was created: Claude Code analyzed the entire codebase - routes, controllers, models, concerns, views, JavaScript, CSS, tests, and configuration. The goal was to extract not just what patterns are used, but why - inferring philosophy from implementation choices.

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class Notifier < ActionMailer::Base
  delivers_from '[email protected]'
  
  def welcome(user)
    @user = user # available to the view
    mail(:subject => 'Welcome!', :to => user.email_address)
    # auto renders both welcome.text.erb and welcome.html.erb
  end
  
  def goodbye(user)

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# MODEL

class Case < ActiveRecord::Base
  include Eventable
  
  has_many :tasks

  concerning :Assignment do
    def assign_to(new_owner:, details:)
      transaction do

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import Foundation

enum Environment: String {
    case development, staging, production
}

extension Environment {
    static var current: Environment {
        if isAppStore {
            return .production

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import * as React from "react";
import { useMousePosition } from "~/hooks/useMousePosition";

/** Component to cover the area between the mouse cursor and the sub-menu, to allow moving cursor to lower parts of sub-menu without the sub-menu disappearing. */
export function MouseSafeArea(props: { parentRef: React.RefObject<HTMLDivElement> }) {
  const { x = 0, y = 0, height: h = 0, width: w = 0 } = props.parentRef.current?.getBoundingClientRect() || {};
  const [mouseX, mouseY] = useMousePosition();
  const positions = { x, y, h, w, mouseX, mouseY };
  return (
    <div

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import { Controller } from "stimulus";
import { get } from "@rails/request.js";
import { PageSnapshot } from "@hotwired/turbo";

export default class extends Controller {
  static values = { hoverTime: Number };
  connect() {
    this.element.addEventListener("mouseover", this.prefetch.bind(this));
    this.element.addEventListener("touchstart", this.prefetch.bind(this));
  }

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class Ticket < ActiveRecord::Base
  belongs_to :grouper
  belongs_to :user

  validate :user_cant_be_blacklisted, on: :confirmation
  validate :user_cant_double_book, on: :confirmation

  validate :grouper_cant_be_full, on: :confirmation
  validate :grouper_cant_have_occurred, on: :confirmation

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/*
  ERB template chunk from The Feed's display of emails:

  <section class="postings postings--feed-style" id="postings"
      data-controller="pagination" data-pagination-root-margin-value="40px">
    <%= render partial: "postings/snippet", collection: @page.records, as: :posting, cached: true %>

    <%= link_to(spinner_tag, url_for(page: @page.next_param),
          class: "pagination-link", data: { pagination_target: "nextPageLink", preload: @page.first? }) unless @page.last? %>
  </section>

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export default class extends ApplicationController {
  print() {
    window.print()
  }

  scrollToTop() {
    window.scrollTo({ top: 0, behavior: "smooth" })
  }

  confirm(event) {

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[Unit]
Description=Puma HTTP Server
After=network.target

# Uncomment for socket activation (see below)
# Requires=puma.socket

[Service]
Type=simple