Claude Code Hooks

Shell commands that fire at specific points in Claude Code's lifecycle.

Hooks enforce mechanically what prose cannot: a model can reason its way past an instruction, but it cannot reason its way past an exit 2 — which is exactly why every hook must be narrow, silent, and reversible.

Named failure mode — chatty happy path: a hook that emits stdout on exit 0 corrupts the tool call it was guarding; silence on success is part of the contract, not a style preference.

Constraints

• Enforcement hooks (the PreToolUse policy dispatcher) ship by DEFAULT: plugin installs auto-wire hooks/hooks.json; skill copies and checkouts wire with one command (scripts/install-hooks.sh). Operators can disable per host (/plugin disable, or remove the settings matchers).
• Injection hooks (SessionStart/UserPromptSubmit context stuffing) stay dead — the #511 teardown proved delta=0 at 10.35M resident tokens. Never ship one; the hookless-cold-start gate still enforces this.
• Keep the happy path silent and block only with the event's documented exit/JSON contract because stray stdout can corrupt a tool call.
• Bound Stop hooks with stop_hook_active and scope matchers narrowly to prevent recursion and unrelated-command interception.