Hooks: Automating Reactions To Tool Calls

Hooks let you run scripts before or after Claude Code does anything. They're how you turn 'guidance' into 'enforcement' — or how you debug what the agent is doing.

10 min · Reviewed 2026

What hooks are

A hook is a small script Claude Code runs at a defined point in its lifecycle — before a tool call, after a tool call, when a session starts, when it stops. The hook can read what the agent is about to do, transform it, log it, or block it. Hooks are how you turn project rules from optional suggestions into enforced behavior.

The lifecycle events

Event	Fires when	Use it for
PreToolUse	Before any tool call	Block, transform, or log
PostToolUse	After any tool call	Validate result, audit
UserPromptSubmit	When you submit a message	Inject context, log queries
SessionStart	On `claude` start	Pull in project state
Stop	Session end	Cleanup, summary, audit log

Three hooks worth building

PreToolUse blocking destructive bash: refuse `rm -rf`, `git push --force`, `db:reset` unless explicit confirmation
PostToolUse format-on-edit: run Prettier or Biome after every Edit so files always land formatted
UserPromptSubmit context injection: pre-pend the result of `git status` so every prompt has fresh repo state

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": { "tool": "Bash" },
        "command": "./scripts/block-destructive.sh"
      }
    ],
    "PostToolUse": [
      {
        "matcher": { "tool": "Edit" },
        "command": "pnpm prettier --write $CLAUDE_TOUCHED_FILE"
      }
    ]
  }
}A minimal hooks block. The matcher decides which tool calls fire the hook; the command runs the script.

Where hooks beat CLAUDE.md

CLAUDE.md says 'don't push to main directly.' A hook BLOCKS pushes to main, period. Anywhere the cost of a mistake is high enough that 'usually respects' isn't good enough, a hook is the right answer. The model is no longer the only line of defense.

The big idea: prompts persuade, hooks enforce. Build hooks for the rules you actually need to hold.

End-of-lesson check

15 questions · take it digitally for instant feedback at tendril.neural-forge.io/learn/quiz/end-claude-code-hooks-creators

What is the core idea behind "Hooks: Automating Reactions To Tool Calls"?
1. Hooks let you run scripts before or after Claude Code does anything. They're how you turn 'guidance' into 'enforcement' — or how you debug what the agent is doing.
2. Selection-aware prompts (highlight code, ask about it, the model gets the select…
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
Which term best describes a foundational idea in "Hooks: Automating Reactions To Tool Calls"?
1. PreToolUse
2. hook
3. PostToolUse
4. lifecycle event
A learner studying Hooks: Automating Reactions To Tool Calls would need to understand which concept?
1. hook
2. PostToolUse
3. PreToolUse
4. lifecycle event
Which of these is directly relevant to Hooks: Automating Reactions To Tool Calls?
1. hook
2. PreToolUse
3. lifecycle event
4. PostToolUse
Which of the following is a key point about Hooks: Automating Reactions To Tool Calls?
1. PreToolUse blocking destructive bash: refuse `rm -rf`, `git push --force`, `db:reset` unless explici…
2. PostToolUse format-on-edit: run Prettier or Biome after every Edit so files always land formatted
3. UserPromptSubmit context injection: pre-pend the result of `git status` so every prompt has fresh re…
4. Selection-aware prompts (highlight code, ask about it, the model gets the select…
What is the key insight about "Configured in settings.json" in the context of Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Hooks are wired up in your settings.json (project-scoped or user-scoped).
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
What is the key insight about "Hooks can hang the agent" in the context of Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Tasks that are short enough to do inline (under 5-10k tokens of effort)
3. If a hook script blocks indefinitely, the whole session blocks.
4. worktree
What is the key insight about "From the community" in the context of Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Tasks that are short enough to do inline (under 5-10k tokens of effort)
3. worktree
4. On r/ClaudeAI, the recurring 'first three hooks to ship' list is identical across teams: PostToolUse formatter on Edit (…
Which statement accurately describes an aspect of Hooks: Automating Reactions To Tool Calls?
1. A hook is a small script Claude Code runs at a defined point in its lifecycle — before a tool call, after a tool call, when a session starts…
2. Selection-aware prompts (highlight code, ask about it, the model gets the select…
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
What does working with Hooks: Automating Reactions To Tool Calls typically involve?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. CLAUDE.md says 'don't push to main directly.' A hook BLOCKS pushes to main, period.
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
Which of the following is true about Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Tasks that are short enough to do inline (under 5-10k tokens of effort)
3. The big idea: prompts persuade, hooks enforce. Build hooks for the rules you actually need to hold.
4. worktree
Which best describes the scope of "Hooks: Automating Reactions To Tool Calls"?
1. It is unrelated to tools workflows
2. It applies only to the opposite beginner tier
3. It was deprecated in 2024 and no longer relevant
4. It focuses on Hooks let you run scripts before or after Claude Code does anything. They're how you turn 'guidance'
Which section heading best belongs in a lesson about Hooks: Automating Reactions To Tool Calls?
1. The lifecycle events
2. Selection-aware prompts (highlight code, ask about it, the model gets the select…
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
Which section heading best belongs in a lesson about Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Three hooks worth building
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
Which section heading best belongs in a lesson about Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Tasks that are short enough to do inline (under 5-10k tokens of effort)
3. Where hooks beat CLAUDE.md
4. worktree

← Back to interactive lesson

Tendril · Creators · Tools Literacy

Hooks: Automating Reactions To Tool Calls

Hooks let you run scripts before or after Claude Code does anything. They're how you turn 'guidance' into 'enforcement' — or how you debug what the agent is doing.

10 min · Reviewed 2026

What hooks are

The lifecycle events

Event	Fires when	Use it for
PreToolUse	Before any tool call	Block, transform, or log
PostToolUse	After any tool call	Validate result, audit
UserPromptSubmit	When you submit a message	Inject context, log queries
SessionStart	On `claude` start	Pull in project state
Stop	Session end	Cleanup, summary, audit log

Three hooks worth building

PreToolUse blocking destructive bash: refuse `rm -rf`, `git push --force`, `db:reset` unless explicit confirmation
PostToolUse format-on-edit: run Prettier or Biome after every Edit so files always land formatted
UserPromptSubmit context injection: pre-pend the result of `git status` so every prompt has fresh repo state

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": { "tool": "Bash" },
        "command": "./scripts/block-destructive.sh"
      }
    ],
    "PostToolUse": [
      {
        "matcher": { "tool": "Edit" },
        "command": "pnpm prettier --write $CLAUDE_TOUCHED_FILE"
      }
    ]
  }
}A minimal hooks block. The matcher decides which tool calls fire the hook; the command runs the script.

Where hooks beat CLAUDE.md

The big idea: prompts persuade, hooks enforce. Build hooks for the rules you actually need to hold.

End-of-lesson check

15 questions · take it digitally for instant feedback at tendril.neural-forge.io/learn/quiz/end-claude-code-hooks-creators

What is the core idea behind "Hooks: Automating Reactions To Tool Calls"?
1. Hooks let you run scripts before or after Claude Code does anything. They're how you turn 'guidance' into 'enforcement' — or how you debug what the agent is doing.
2. Selection-aware prompts (highlight code, ask about it, the model gets the select…
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
Which term best describes a foundational idea in "Hooks: Automating Reactions To Tool Calls"?
1. PreToolUse
2. hook
3. PostToolUse
4. lifecycle event
A learner studying Hooks: Automating Reactions To Tool Calls would need to understand which concept?
1. hook
2. PostToolUse
3. PreToolUse
4. lifecycle event
Which of these is directly relevant to Hooks: Automating Reactions To Tool Calls?
1. hook
2. PreToolUse
3. lifecycle event
4. PostToolUse
Which of the following is a key point about Hooks: Automating Reactions To Tool Calls?
1. PreToolUse blocking destructive bash: refuse `rm -rf`, `git push --force`, `db:reset` unless explici…
2. PostToolUse format-on-edit: run Prettier or Biome after every Edit so files always land formatted
3. UserPromptSubmit context injection: pre-pend the result of `git status` so every prompt has fresh re…
4. Selection-aware prompts (highlight code, ask about it, the model gets the select…
What is the key insight about "Configured in settings.json" in the context of Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Hooks are wired up in your settings.json (project-scoped or user-scoped).
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
What is the key insight about "Hooks can hang the agent" in the context of Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Tasks that are short enough to do inline (under 5-10k tokens of effort)
3. If a hook script blocks indefinitely, the whole session blocks.
4. worktree
What is the key insight about "From the community" in the context of Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Tasks that are short enough to do inline (under 5-10k tokens of effort)
3. worktree
4. On r/ClaudeAI, the recurring 'first three hooks to ship' list is identical across teams: PostToolUse formatter on Edit (…
Which statement accurately describes an aspect of Hooks: Automating Reactions To Tool Calls?
1. A hook is a small script Claude Code runs at a defined point in its lifecycle — before a tool call, after a tool call, when a session starts…
2. Selection-aware prompts (highlight code, ask about it, the model gets the select…
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
What does working with Hooks: Automating Reactions To Tool Calls typically involve?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. CLAUDE.md says 'don't push to main directly.' A hook BLOCKS pushes to main, period.
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
Which of the following is true about Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Tasks that are short enough to do inline (under 5-10k tokens of effort)
3. The big idea: prompts persuade, hooks enforce. Build hooks for the rules you actually need to hold.
4. worktree
Which best describes the scope of "Hooks: Automating Reactions To Tool Calls"?
1. It is unrelated to tools workflows
2. It applies only to the opposite beginner tier
3. It was deprecated in 2024 and no longer relevant
4. It focuses on Hooks let you run scripts before or after Claude Code does anything. They're how you turn 'guidance'
Which section heading best belongs in a lesson about Hooks: Automating Reactions To Tool Calls?
1. The lifecycle events
2. Selection-aware prompts (highlight code, ask about it, the model gets the select…
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
Which section heading best belongs in a lesson about Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Three hooks worth building
3. Tasks that are short enough to do inline (under 5-10k tokens of effort)
4. worktree
Which section heading best belongs in a lesson about Hooks: Automating Reactions To Tool Calls?
1. Selection-aware prompts (highlight code, ask about it, the model gets the select…
2. Tasks that are short enough to do inline (under 5-10k tokens of effort)
3. Where hooks beat CLAUDE.md
4. worktree

← Back to interactive lesson