The startup sequence from binary launch to ready-to-accept-input. Optimized to feel instant — parallelizes subprocess spawns, defers heavy modules, and fast-paths simple commands like --version.

Gathers everything the model needs to know about your project, preferences, and environment. Runs before every API call to build an accurate, up-to-date system prompt.

The brain of Claude Code. Sends messages to the Anthropic API, processes streaming responses, manages the tool call loop, and handles context compression when conversations get long.

40+ tools that give Claude the ability to act — read files, write code, run commands, search the web, spawn sub-agents, and more. Every tool goes through a permission check before execution.

A full React application running in your terminal via Ink. Manages the REPL loop, renders markdown, shows diffs, displays agent progress, handles keyboard shortcuts, and bridges to IDEs.