Claude Code is a CLI tool powered by Anthropic's Claude model family (currently Claude Sonnet and Opus tiers) that provides agentic code execution capabilities. It communicates with the Anthropic API and is granted controlled access to the local file system and shell, enabling it to read/write source files, execute test suites, run build pipelines, and interact with git. The tool follows an agent loop — planning, acting, observing, and iterating — to complete tasks described in natural language. It surfaces tool-use calls transparently, allowing developers to review and approve actions before execution.