How Claude Code Works - Deep Dive

Claude Code is Anthropic's terminal AI programming assistant that goes beyond coding to help with anything you can do from the command line: writing documentation, running builds, searching files, researching topics, and more. This article provides a comprehensive analysis of its core architecture and working principles.

Core Architecture: The Agent Loop

When you give Claude a task, it goes through three interwoven phases:

1. Gathering Context

Claude first searches files and understands code structure to collect all information needed to complete the task.

2. Taking Action

Based on gathered information, Claude performs specific operations: editing files, running commands, searching the web, etc.

3. Validating Results

Claude runs tests and checks outputs to ensure operations achieve the expected results.

This loop adapts automatically to your requirements:

Simple questions (e.g., codebase queries): May only need context gathering
Bug fixes: Cycle through all three phases multiple times
Refactoring tasks: May involve extensive validation

Claude determines what each step needs based on what it learned from previous steps, chaining dozens of operations together and correcting course along the way. You can interrupt the loop at any time to guide Claude in a different direction.

Two Core Components

Models

Claude Code uses the Claude model family (Sonnet/Opus) to understand code and reason about tasks:

Sonnet: Handles most coding tasks well
Opus: Provides stronger reasoning for complex architectural decisions

You can switch models during a session using /model or specify at startup with claude --model <name>.

Tools

Tools are what make Claude Code an agent. Without tools, Claude could only respond with text; with tools, Claude can:

Tool Category	Capabilities
File Operations	Read files, edit code, create new files, rename and reorganize
Search	Find files by pattern, search content with regex, explore codebase
Execution	Run shell commands, start servers, run tests, use git
Web	Search the web, fetch documentation, look up error messages
Code Intelligence	View type errors and warnings, jump to definitions, find references

Claude chooses which tools to use based on your prompts and what it learns along the way. For example, when you say "fix the failing test," Claude might:

Run the test suite to see what's failing
Read the error output
Search for relevant source files
Read those files to understand the code
Edit files to fix the issue
Run tests again to verify

What Claude Can Access

When you run claude in a directory, Claude Code can access:

Project Files

Your entire codebase (files in the directory and subdirectories)
Not just the currently open file—can work across files

Terminal Environment

Any command-line tool: build tools, git, package managers, system utilities, scripts
If you can do it from the command line, Claude can too

Git Status

Current branch, uncommitted changes
Recent commit history

Memory and Instructions

CLAUDE.md: Project-specific instructions, conventions, and context
Auto-memory: Content Claude automatically saves while working (project patterns, preferences, etc.)

Extensions

MCP servers (external service connections)
Skills (workflow automation)
Subagents (task delegation)

Execution Environments

Claude Code runs in three environments:

Environment	Code Runs On	Use Case
Local	Your machine	Default. Full access to files, tools, and environment
Cloud	Anthropic-managed VMs	Offload tasks, work with repos you don't have locally
Remote Control	Your machine, controlled from browser	Use web UI while keeping everything local

Session Management

Session Persistence

Claude Code saves your conversation history: every message, tool use, and result is stored. This enables rollback, resuming, and forking sessions.

Session Independence

Each new session starts with a fresh context window, with no conversation history from previous sessions. But Claude can maintain learning across sessions using auto-memory.

Common Commands

# Resume last session
claude --continue

# Resume specific session
claude --resume

# Fork session to try different approach
claude --continue --fork-session

Context Window Management

Claude's context window holds: conversation history, file contents, command output, CLAUDE.md, loaded skills, etc.

When context fills up, Claude automatically:

First clears older tool outputs
Then summarizes conversations (preserving requests and key code snippets)

Recommendation: Put persistent rules in CLAUDE.md rather than relying on conversation history.

Safety Mechanisms

Checkpoints

Every file edit is reversible
Claude automatically snapshots current content before editing
Press Esc twice to revert to previous state
Applies only to file changes, not remote system operations

Permission Control

Press Shift+Tab to cycle through permission modes:

Mode	Description
Default	Ask before file edits and shell commands
Auto-accept edits	Edit files without asking, still ask for commands
Plan Mode	Use read-only tools only, create plan for approval before execution

You can also configure specific commands to auto-execute in .claude/settings.json.

Best Practices

1. It's a Conversation

You don't need perfect prompts. Start with what you want, then iterate:

You: Fix the login error
Claude: [Investigates, attempts fix]
You: That's not quite right. The issue is in session handling.
Claude: [Adjusts approach]

2. Be Specific Upfront

The more precise your initial prompt, the fewer corrections needed:

The checkout flow is broken for users with expired cards.
Check src/payments/ for the issue, especially token refresh.
Write a failing test first, then fix it.

3. Give Claude Something to Validate

Claude performs better when it can check its own work:

Implement validateEmail. Test cases:
'[email protected]' → true
'invalid' → false
'test@' → false
Run tests after.

4. Explore Before Implementing

For complex problems, separate research from coding:

Read src/auth/ and understand how we handle sessions.
Then create a plan for adding OAuth support.

5. Delegate, Don't Instruct

Treat it like delegating to a capable colleague:

The checkout flow is broken for users with expired cards.
Relevant code is in src/payments/. Can you investigate and fix it?

Extension Features

Beyond built-in tools, Claude Code supports:

Skills: Custom workflows and commands
MCP: Connect to external services
Subagents: Delegate tasks to specialized agents
Hooks: Automate workflows

Summary

At its core, Claude Code is an agentic tool—it transforms a language model into an agent capable of coding. Through the agent loop, rich toolset, and intelligent context management, Claude Code helps developers:

Quickly understand complex codebases
Make coordinated edits across files
Automate repetitive tasks
Complete the full workflow from coding to deployment through conversation

Mastering these working principles will help you use Claude Code more effectively, making it a powerful assistant for your development work.

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