Claude Code: Claude Code Introduction and How It Works

Last updated: 2026-08-31

Claude Code is Anthropic's AI coding Agent — it's not a chatbot, but an intelligent entity that can read files, run tests, modify code, and iterate based on feedback.

📋 Prerequisites: No prior knowledge required, basic command line familiarity helpful

1. What You'll Learn

• Claude Code's positioning: Agent, not Chat
• How it works in local code repositories
• Core architecture and permission model
• Comparison with traditional AI coding tools
• Use cases and limitations

About Code Example Outputs

This course uses a deterministic/non-deterministic separation pattern for code examples, which is the industry best practice for AI Agent tool tutorials:

2. A Real Team's Story

(1) The Problem: AI Coding Tool Efficiency Bottleneck

Alice is the tech lead at a mid-sized internet company. Her team tried various AI coding tools:

• ChatGPT: Good answers, but code needs manual copy-paste into the project
• GitHub Copilot: Convenient auto-completion, but only local completion, can't understand the whole project
• Cursor: Good IDE integration, but limited Agent capabilities for complex refactoring

Product manager Bob's requirements keep growing:

"We need to migrate the entire authentication module from Session to JWT, involving 20+ files, and ensure all tests pass."

(2) Claude Code's Solution

Alice installed Claude Code and launched the migration with one command:

claude "Migrate the authentication module from Session to JWT, ensure all tests pass"

Claude Code autonomously completed:

1. Read project structure, located all authentication-related files
2. Modified authentication logic one by one
3. Ran the test suite
4. Fixed code based on failed results
5. Iterated until all tests passed

Files modified: 23
Tests run: 47
Tests passed: 47
Iterations: 3
Time: ~8 minutes

3. What is Claude Code

(1) Core Definition

Claude Code is a command-line AI Agent that works directly in your local code repository:

(2) Agent vs Chat: The Essential Difference

graph LR
    A[User Instruction] --> B[Chat Mode]
    A --> C[Agent Mode]
    B --> B1[Generate Answer]
    B1 --> B2[User Manually Executes]
    C --> C1[Understand Intent]
    C1 --> C2[Read Context]
    C2 --> C3[Execute Operation]
    C3 --> C4[Verify Result]
    C4 --> C5{Success?}
    C5 -->|No| C2
    C5 -->|Yes| C6[Report Result]

graph LR
    A[User Instruction] --> B[Chat Mode]
    A --> C[Agent Mode]
    B --> B1[Generate Answer]
    B1 --> B2[User Manually Executes]
    C --> C1[Understand Intent]
    C1 --> C2[Read Context]
    C2 --> C3[Execute Operation]
    C3 --> C4[Verify Result]
    C4 --> C5{Success?}
    C5 -->|No| C2
    C5 -->|Yes| C6[Report Result]

▶ Example 1: Chat vs Agent Comparison

# Chat approach: User needs multiple steps
# 1. Ask AI how to fix bug
# 2. Copy code
# 3. Paste into file
# 4. Run test
# 5. Test fails, go back to step 1

# Agent approach: One command does it all
claude "Fix the null pointer exception in user.service.ts, ensure tests pass"

4. How Claude Code Works

(1) Workflow

Claude Code's work loop:

graph TB
    U[User Input] --> P[Intent Parsing]
    P --> R[Read Project Context]
    R --> A[Plan Operations]
    A --> E[Execute Operations]
    E --> V[Verify Results]
    V --> S{Success?}
    S -->|Yes| RPT[Report Results]
    S -->|No| A

graph TB
    U[User Input] --> P[Intent Parsing]
    P --> R[Read Project Context]
    R --> A[Plan Operations]
    A --> E[Execute Operations]
    E --> V[Verify Results]
    V --> S{Success?}
    S -->|Yes| RPT[Report Results]
    S -->|No| A

(2) Permissions and Security

Claude Code has high permissions but provides multi-layer security controls:

▶ Example 2: Claude Code Work Process

$ claude "Create date.ts under src/utils/ with common date formatting functions and tests"

# Claude Code's autonomous work process:
# 1. Reading src/utils/ directory structure...
# 2. Reading existing utils for style consistency...
# 3. Creating src/utils/date.ts with formatDate(), relativeTime(), etc.
# 4. Creating src/utils/__tests__/date.test.ts
# 5. Running: npm test -- src/utils/__tests__/date.test.ts
# 6. 2 tests failing... fixing edge cases
# 7. Running: npm test -- src/utils/__tests__/date.test.ts
# 8. All 6 tests passed ✓

5. Comparison with Other AI Coding Tools

▶ Example 3: Alice's Tool Evaluation

def evaluate_tool(tool_name, agent_score, scope_score, multi_file):
    score = agent_score * 0.4 + scope_score * 0.3 + (1 if multi_file else 0) * 0.3
    return round(score, 2)

tools = {
    "Claude Code": {"agent": 9, "scope": 9, "multi_file": True},
    "Copilot": {"agent": 3, "scope": 4, "multi_file": False},
    "Cursor": {"agent": 6, "scope": 7, "multi_file": True},
    "Aider": {"agent": 7, "scope": 8, "multi_file": True},
}

for name, scores in tools.items():
    result = evaluate_tool(name, scores["agent"], scores["scope"], scores["multi_file"])
    print(f"{name}: {result}")

6. Comprehensive Example: Project-Level Refactoring

# Scenario: Alice needs to migrate an Express project to Fastify

$ claude "Migrate the entire project from Express to Fastify:
1. Replace all route definitions
2. Update middleware syntax
3. Modify startup script
4. Ensure all tests pass
5. Update package.json dependencies"

# Claude Code autonomously executes:
# → Scanning 45 files for Express patterns...
# → Converting route definitions (32 routes)...
# → Updating middleware (8 files)...
# → Running test suite: 89/89 passed ✓
# → Updating package.json...
# → Removing Express dependencies...
# → Final test run: 89/89 passed ✓

❓ FAQ

📖 Summary

• Claude Code is an Agent tool, not a chat tool — core ability is autonomous code operations
• Work loop: Read → Analyze → Execute → Verify → Iterate
• High permissions with multi-layer security controls, configurable auto/manual confirmation
• CLI-based, not IDE-dependent, works directly in terminal
• Best for multi-file refactoring, bug fixing, test writing and other complex tasks

📝 Exercises

1. Basic (⭐): List three core differences between Claude Code and ChatGPT in coding assistance.
2. Intermediate (⭐⭐): Choose an AI coding tool for your project and write your reasoning (refer to the comparison table).
3. Advanced (⭐⭐⭐): Design a workflow specifying which tasks suit Claude Code and which suit Copilot, with decision criteria.

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