The 11 steps that run every time you press Enter in Claude Code

#ai #python #architecture #programming

Every time you press Enter in Claude Code, an 11-step loop kicks off. Not a simple request-response — a self-directed cycle that keeps running until the task is done.

I spent a few weeks tracing through the source code and turned what I found into a free course. Here's the condensed version of that loop.

The 11 Steps

Step 1 — Input. You type a prompt. The terminal captures the keypress via a custom React renderer (yes, React in a terminal).

Step 2 — Message. Your text becomes a UserMessage object appended to the conversation history.

Step 3 — Memory. CLAUDE.md files from 4 levels (enterprise → user → project → subdirectory) are loaded and concatenated into the system prompt.

Step 4 — System Prompt. Tool definitions, environment info, and memory are merged into the full system prompt.

Step 5 — API Call. Messages + system prompt + tool definitions stream to the Anthropic API. Tokens come back in real time.

Step 6 — Parse. The response is split into content blocks: text, thinking, and tool_use.

Step 7 — Decision. Does the response contain tool_use blocks? If yes → execute tools. If only text → done, return to user.

Step 8 — Execute. Each tool is found in the registry, validated against its JSON Schema, permission-checked (allow/ask/deny), then executed. Read-only tools run in parallel; write tools run one at a time.

Step 9 — Result. Tool outputs are wrapped as UserMessage objects (the API requires strict user/assistant alternation).

Step 10 — Loop. Updated history goes back to Claude. The loop continues until no more tool calls.

Step 11 — Render. Final text streams to the terminal. The screen buffer diffs and redraws only changed cells.

What surprised me

The agent loop itself is simple. The complexity lives in error recovery and retry logic (5 different retry strategies for different error types).
There are 50+ tools, and read-only tools run concurrently while write tools get exclusive access.
The source has ~8 unreleased features: a terminal companion pet (Buddy), persistent memory mode (Kairos), multi-agent teams, and more.
Context compaction automatically summarizes old messages when the window fills up — there's a reactive safety net that catches prompt-too-long errors.