add-hook

A command for adding a hook to a Claude Code plugin. A hook is an automated action that runs when a specified event happens, such as before or after a tool is used.

In plain words
What is it for?
Use it to add or update automation for events such as tool use, session start or end, submitted prompts, notifications, or compaction. It supports an optional pattern for limiting which actions trigger the hook.
Why use it?
It avoids hand-editing the hooks configuration and helps connect the automation to the right event and matching pattern. It can also create the hooks folder when needed.

Command

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add commands/ivan-magda/claude-code-plugin-template/add-hook
Clone the repo
git clone --depth 1 https://github.com/ivan-magda/claude-code-plugin-template
Per session 11 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 3,424 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00011 $0.03424
Opus 5 $0.00005 $0.01712
Sonnet 5 $0.00002 $0.00685
Haiku 4.5 $0.00001 $0.00342

Measured 2d ago against content hash c95788081fe1, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

add-hook scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

2 near-identical copies found in the catalogue:

  • add-hook — 98% identical, 4 lines differ
  • add-hook — 98% identical, 4 lines differ
plugins/plugin-development/commands/add-hook.md · 452 lines

How it starts

The opening of the file, as written. The whole thing — 452 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Add Hook

Add or update hooks.json with a new hook configuration for automated behavior.

Arguments

  • $1 (required): Event type (PreToolUse, PostToolUse, SessionStart, SessionEnd, UserPromptSubmit, Notification, Stop, SubagentStop, or PreCompact)
  • $2 (optional): Matcher pattern (e.g., Write|Edit or .*)
  • --plugin=<plugin-name> (optional): Specify which plugin to add the hook to

Usage:

# From within a plugin directory
/plugin-development:add-hook PreToolUse "Write|Edit"

# From marketplace root, specifying plugin
/plugin-development:add-hook PreToolUse "Write|Edit" --plugin=plugin-development

Template Variables

When generating hook configurations and scripts:

  • $1: Event type
  • $2: Matcher pattern (or default based on event type)
  • ${CLAUDE_PLUGIN_ROOT}: Plugin root path (use in all hook commands)

Prerequisites

  • Must be run from either:
    • A plugin root directory (containing .claude-plugin/plugin.json), OR
    • A marketplace root directory (containing .claude-plugin/marketplace.json)
  • hooks/ directory will be created if needed

Instructions

Validation

IMPORTANT: When running test commands for validation (checking directories, files, etc.), use require_user_approval: false since these are read-only checks.

  1. Detect context and target plugin (output thoughts during this process):

    a. Check if we're in a plugin directory:

    • Look for .claude-plugin/plugin.json in current directory
    • Output: "Checking for plugin directory..."
    • If found:
      • Output: "Found plugin.json - using current directory as target plugin"
      • Use current directory as target plugin
    • If not found:
      • Output: "Not in a plugin directory, checking for marketplace..."

    b. If not in plugin directory, check if we're in marketplace root:

    • Look for .claude-plugin/marketplace.json in current directory
    • If found:
      • Output: "Found marketplace.json - this is a marketplace root"
      • This is a marketplace root
    • If not found:
      • Output: "Error: Neither plugin.json nor marketplace.json found"
      • Show error and exit

Read the full file on GitHub · 452 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 452 lines · 0 tokens per session scan A c95788081fe1

Subscribe to this mod's changes

add-hook is a command published in the GitHub repository ivan-magda/claude-code-plugin-template (68 stars, last pushed 2mo ago), licensed MIT. It adds 11 tokens to every session and 3,424 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.