Claude Code: The Complete Guide
Master the agentic loop, context window, permission modes, and tools. From your first prompt to advanced workflows across every language and framework.
What Is Claude Code?
Claude Code is an AI agent that runs on an agentic loop—gathering context, taking action, and verifying results. Unlike older AI tools that just answer questions, Claude Code actively reads your codebase, edits files, runs commands, and iterates until it achieves your goal.
The core of Claude Code is simple: you describe what you want, and it uses a repeating 4-step loop to deliver it. Understand this loop, and you unlock the tool's full power.
The Agentic Loop: 4 Steps That Repeat
Every interaction follows the same pattern:
Prompt
You describe what you need. That goal is what the entire loop works toward.
Gather Context
Claude Code reads your project—files, dependencies, errors—to understand the landscape.
Take Action
It edits files, runs commands, and makes real changes to your project.
Verify
It checks if the result meets your prompt. Met? Stop. Not yet? Loop back and iterate.
The Context Window: Your Working Memory
Claude Code operates inside a context window—a limit on how much information it can hold at once. Think of it as working memory. When you start a session, the context is mostly empty. As Claude Code reads files and runs commands, the window fills up.
If Claude Code hits the window limit mid-task, it auto-compacts: summarizing what's happened and dropping details it no longer needs. This keeps the conversation going without losing critical state.
Permission Modes: How Much Control Do You Keep?
By default, Claude Code asks explicit permission before editing a file or running a command. Three modes let you adjust this:
Default: Ask Permission
Claude Code asks before every file edit or command run. Safest for new work.
Auto-Accept Edits (Shift+Tab)
File edits go through automatically; commands still ask. Faster for trusted changes.
Plan Mode (Shift+Tab again)
Read-only tools only—Claude Code drafts a plan before any change. Review the approach with zero risk.
Tools: What Claude Code Can Do
Claude Code accesses tools to interact with your project:
- Read files — examine code, config, and docs
- Edit files — make targeted changes
- Run commands — test, build, deploy, and debug
- Search code — find patterns and symbols
- Web fetch — pull docs and real-time data (when needed)
Each tool call is transparent—you see what Claude Code did, and you approve before it affects your project.
Practical Patterns by Language
Claude Code works across every language. Here's how to get the most from it:
TypeScript / JavaScript (Node.js + Next.js)
Use TypeScript for type safety. Keep Claude Code focused—describe one feature at a time. Leverage tsc --noEmit to catch type errors before asking Claude Code to run code.
Python
Test-driven development (write tests first) works best. Claude Code can run pytest to verify code as it writes. Always pin dependency versions in requirements.txt.
Rust
The Rust compiler is your assistant—let it guide Claude Code. Write small tests and ask Claude Code to compile incrementally. Use cargo as your feedback loop.
Best Practices
1. One Task at a Time
Break big goals into smaller prompts. "Add user auth" is vague; "Add email/password login to the signup form" is clear.
2. Read Before Asking
If you point Claude Code at a file first ("Read this file, then modify X"), it understands context better and makes fewer mistakes.
3. Use Tests as Guardrails
Write tests for critical paths. When Claude Code sees a test suite, it knows exactly what success looks like.
4. Verify Before Merging
Always run your builds and tests after Claude Code finishes. The agentic loop is smart, but human eyes catch edge cases.
Frequently Asked Questions
Can Claude Code delete my files?
Only with your permission. By default, Claude Code asks before any destructive action. Use Plan mode if you want an extra safety layer.
What's the difference between auto-accept edits and plan mode?
Auto-accept edits skips the permission prompt (faster for trusted work). Plan mode skips edits entirely until you approve the plan (safer for big changes).
Does Claude Code work offline?
No. Claude Code calls the Claude API, so you need an internet connection and an API key.
Can I use Claude Code without a subscription?
Claude Code runs on the Claude API via OpenRouter, Anthropic direct, or Fireworks. Pricing depends on the provider and your usage.
Getting Started Today
Open Claude Code, describe what you want to build, and let the agentic loop do the work. Start small—a bug fix, a feature addition, a script. You'll build muscle memory for how to interact with Claude Code effectively in minutes.