Benito Serna bhserna

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.

Tips for Money Related Arithmetic in Ruby

Never use float for performing arithmetic calculations relating to money.

Floating numbers can sometimes show funky behaviour. It is not Ruby’s fault but the very implementation of floating numbers raises precision issues.

Examples of odd behaviour:

How do you POST a JSON file with curl??

You can post a json file with curl like so:

curl -X POST -H "Content-Type: application/json" -d @FILENAME DESTINATION

so for example:

	import { Controller } from "@hotwired/stimulus"
	import SignaturePad from 'signature_pad'

	export default class extends Controller {
	static targets = ["canvas", "input"]
	connect() {
	this.signaturePad = new SignaturePad(this.canvasTarget)
	this.signaturePad.addEventListener("endStroke", this.endStroke)
	this.resizeCanvas()
	if (this.inputTarget.value) {

	# frozen_string_literal: true

	require 'bundler/inline'

	gemfile do
	source 'https://rubygems.org'
	gem 'pry'
	gem "sqlite3"
	gem 'activerecord'
	end

	# Take a Markdown email from the clipboard or a file and turn it into HTML
	function mkemail() {
	# Either read from clipboard (default) or read from a file
	if [[ -z $1 ]]; then
	content=`pbpaste`
	echo "Reading from clipboard"
	else
	content=`cat $1`
	echo "Reading from file '$1'"
	fi

	This tool is used to compare microbenchmarks across two versions of code. It's
	paranoid about nulling out timing error, so the numbers should be meaningful.
	It runs the benchmarks many times, scaling the iterations up if the benchmark
	is extremely short, and it nulls out its own timing overhead while doing so. It
	reports results graphically with a text interface in the terminal.

	You first run it with --record, which generates a JSON dotfile with runtimes
	for each of your benchmarks. Then you change the code and run again with
	--compare, which re-runs and generates comparison plots between your recorded
	and current times. In the example output, I did a --record on the master

	# MODEL

	class Case < ActiveRecord::Base
	include Eventable

	has_many :tasks

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

	class AssignCaseCommand < Command

	attribute :case, Case
	attribute :owner, User
	attribute :created_by, User
	attribute :comments, String
	attribute :distribute_at, DateTime
	attribute :distribute_rule_name, String
	attribute :require_initial, Boolean

	require 'spec/support/grep_matcher'

	describe do
	disallow_presence_of pattern: "send(.*#",
	location: "app/",
	description: "Do not use dynamic method invocations",
	failure: "Please change dynamic method call to something more sane."
	end