Claude Code

Claude Code is Anthropic's command-line tool letting Claude work directly in your terminal — reading local files, executing shell commands, modifying code files.

The fundamental difference from claude.ai web is "access scope": in claude.ai, Claude only sees text you paste to it; in Claude Code, Claude can access all files in your project directory and execute any command on your computer (git, pytest, npm run build).

Installation and startup takes three steps: confirm Node.js 18+ is installed (node --version), run npm install -g @anthropic-ai/claude-code, type claude in your project directory to start. First launch guides you through authentication.

Once started, describe tasks in natural language — "find all files over 200 lines in the src directory," "where might this bug be, analyze error.log for me," "add type hints to all functions in utils.py." Claude Code reads relevant files, executes necessary commands, makes modifications — no manual copy-pasting required.

CLAUDE.md is Claude Code's most underestimated feature and the key to making Claude Code genuinely efficient.

CLAUDE.md is a Markdown file in your project root directory that Claude Code reads automatically every session. Put your project background, architecture description, coding conventions, and common commands here — Claude doesn't need to relearn your project every conversation.

A good CLAUDE.md example: project description, architecture (where models/routes/services/tests live), common commands (how to start dev server, run tests, do database migrations), coding conventions (type hints required, docstrings for public functions, Black formatting).

With this file, every time you open Claude Code it immediately knows the project context — no re-introduction needed. This is the key difference between Claude Code being "okay" and "genuinely useful."

Most efficient Claude Code usage approach: "plan before execute."

Many first-time users immediately say "help me do X," then find Claude made changes that don't match expectations, spending time correcting. Better approach:

Ask for a plan first on complex tasks: "I need to add JWT authentication to this Flask app. First tell me your implementation plan — which files to modify, what dependencies to add, how to design the architecture. Confirm the direction before starting." This lets you verify direction before Claude makes extensive code changes.

Use Git as a safety net: before any important modifications, confirm your working directory is clean (git status). If changes aren't what you wanted, git checkout . reverts everything instantly.

Incremental review: break large tasks into small steps; after each step, check git diff, confirm it's right before continuing.

Use slash commands: /clear (reset long context), /cost (check spending), /compact (compress history to save tokens).

How does Claude Code billing work? How can beginners avoid unexpected high bills?

Claude Code bills through your Anthropic API Key by tokens — more files read, longer conversations, higher costs. Default model is Claude Sonnet 4.5 (switchable with /model command).

Main cost drivers: files read (Claude Code reads file content into Context; every word is a token); conversation length (long conversations accumulate long history Context); model used (Opus costs 5× more than Sonnet).

Avoiding unexpected bills: set a monthly spending limit at console.anthropic.com (recommend $20-50 for beginners); use /cost regularly to monitor spending; /clear after completing tasks to reset Context rather than running one very long conversation; for large codebases, only let Claude read files it genuinely needs.

What this means for your development efficiency: most developers feel Claude Code's cost is "one hour of fees saves two or three hours of time." If your daily Claude Code spend is $1-$3 but saves 1-2 hours of debugging and searching, the ROI is very high.