Claude Code Hooks: The Automation Layer Nobody Knows About

I've been running Claude Code in production for months. Parallel agents, autonomous sub-tasks, the whole stack. And for most of that time I ignored one of the most powerful features in the settings file: hooks. Hooks are shell commands that Claude Code executes automatically before or after tool calls, at session start, and at session end. They're not documented prominently. Most people building AI automation pipelines have no idea they exist. Here's what they actually do and how I use them. The hook types Four hook points exist in ~/.claude/settings.json : PreToolUse — runs before any tool call. Can inspect the tool name and input, and can block the call. PostToolUse — runs after any tool call. Gets the output too. SessionStart — runs once when a Claude Code session opens. SessionEnd — runs when the session closes. The configuration structure: { "hooks" : { "PreToolUse" : [ { "matcher" : "Bash" , "hooks" : [ { "type" : "command" , "command" : "python3 /path/to/your/hook.py" } ] } ], "