Claude Code: Architecture Deep Dive

Ever wondered how an AI coding assistant actually works under the hood? This post breaks down the architecture of Claude Code — Anthropic's agentic coding tool that can read your files, run commands, and make edits across your entire project.

Whether you're curious about building AI-powered tools yourself or just want to understand what happens when you ask Claude Code to "fix this bug," this walkthrough covers the key systems that make it all work.

New to Claude Code? Start with our Getting Started with Claude Code tutorial — it covers installation, setup, and your first real tasks.

Video Walkthrough#

The video below walks through each architectural layer, from how Claude Code processes your request to how it decides what tools to use and when to stop:

What's Inside#

Here's a roadmap of what the video covers — each section builds on the last:

  • The Agentic Loop — The core cycle that powers everything: receive your input, think about what to do, use a tool, check the result, and repeat until the task is done
  • Tool System — How Claude Code decides which tool to use (file editing, search, shell commands, etc.) and how new tools get added through a simple plugin interface
  • Context Management — How it keeps track of your conversation, decides what's relevant, and handles the challenge of limited context windows through smart compaction
  • Permission Model — The safety system that controls what Claude Code is allowed to do — from auto-approving safe reads to asking you before running destructive commands
  • Memory System — How Claude Code remembers things across sessions — your preferences, project context, and past decisions — without cluttering the current conversation
  • Sub-Agent Coordination — How complex tasks get broken into parallel subtasks, each handled by a focused agent working in isolation
  • Data Flow — The full journey of a request: from your keyboard, through the model, into tool execution, and back as a response

Key Takeaways#

Claude Code is a large codebase (~512K lines of TypeScript across ~1,884 files), but the architecture boils down to a few repeating patterns:

  1. Simple loop, complex behavior — At its core, it's just: receive → think → act → check → repeat. The sophistication comes from what happens at each step, not from a complicated control flow
  2. Everything is a tool — File edits, searches, shell commands — they're all modeled the same way. This makes the system easy to extend without touching the core loop
  3. Safety is layered — No single check prevents bad actions. Instead, permissions, sandboxing, and user-configurable hooks each catch different categories of risk
  4. Load only what's needed — Context, tools, and file contents are fetched lazily. This keeps responses fast and avoids wasting the model's attention on irrelevant information