Rik Watson rikwatson

Inside the Claude Code source

Anthropic's Claude Code CLI source code leaked onto GitHub recently. All of it. About 1,900 files and a lot of TypeScript.

I read through the key modules. What follows is a breakdown of the surprising parts: how the system actually works, where Anthropic made clever engineering choices, and where their approach diverges from OpenAI's Codex in ways you wouldn't guess from using either tool.

Lifecycle of a request

Here's what happens when you type a message into Claude Code:

Purpose

Bootstrap knowledge of LLMs ASAP. With a bias/focus to GPT.

Avoid being a link dump. Try to provide only valuable well tuned information.

Prelude

Neural network links before starting with transformers.

This document shows how to mount an AWS S3 bucket on Mac OS X using goofyfs.

The first three steps illustrate how to use goofys

Install goofyfs via brew

brew cask install osxfuse
brew install goofys

Super fast, keyboard-optimized, client side Hugo search

This is a fork of and builds upon the work of Eddie Webb's search and Matthew Daly's search explorations.

It's built for the Hugo static site generator, but could be adopted to function with any json index.

To see it in action, go to craigmod.com and press CMD-/ and start typing.

58 bytes of CSS to look great nearly everywhere

When making this website, i wanted a simple, reasonable way to make it look good on most displays. Not counting any minimization techniques, the following 58 bytes worked well for me:

main {
  max-width: 38rem;
  padding: 2rem;
  margin: auto;
}

2019 update: this essay has been updated on my personal site, together with a followup on how to get started

2020 update: I'm now writing a book with updated versions of all these essays and 35 other chapters!!!!

1. Learn in public

If there's a golden rule, it's this one, so I put it first. All the other rules are more or less elaborations of this rule #1.

You already know that you will never be done learning. But most people "learn in private", and lurk. They consume content without creating any themselves. Again, that's fine, but we're here to talk about being in the top quintile. What you do here is to have a habit of creating learning exhaust. Write blogs and tutorials and cheatsheets. Speak at meetups and conferences. Ask and answer things on Stackoverflow or Reddit. (Avoid the walled gardens like Slack and Discourse, they're not public). Make Youtube videos

	You are a powerful agentic AI coding assistant, powered by Claude 3.5 Sonnet. You operate exclusively in Cursor, the world's best IDE.

	You are pair programming with a USER to solve their coding task.
	The task may require creating a new codebase, modifying or debugging an existing codebase, or simply answering a question.
	Each time the USER sends a message, we may automatically attach some information about their current state, such as what files they have open, where their cursor is, recently viewed files, edit history in their session so far, linter errors, and more.
	This information may or may not be relevant to the coding task, it is up for you to decide.
	Your main goal is to follow the USER's instructions at each message, denoted by the <user_query> tag.

	<communication>
	1. Be conversational but professional.

	// Credit for the basics:
	// https://github.com/oakserver/oak/blob/main/examples/routingServer.ts
	// Setup: Install deno
	// Usage: deno run -A ./DenoPost.ts
	// Use e.g. Postman to POST the json payload to http://127.0.0.1:8000/book
	// Use e.g. any browser to read the json in memory: http://127.0.0.1:8000/book

	import {
	bold,
	cyan,

	(function (context, trackingId, options) {
	const history = context.history;
	const doc = document;
	const nav = navigator \|\| {};
	const storage = localStorage;
	const encode = encodeURIComponent;
	const pushState = history.pushState;
	const typeException = 'exception';
	const generateId = () => Math.random().toString(36);
	const getId = () => {

	# Reduce noisy generated dependency diffs.
	package-lock.json -diff
	pnpm-lock.yaml -diff
	yarn.lock -diff

	# Prefer the current branch's copy on merge conflicts for local config.
	config.json merge=ours