add-hook

add-hook is a command for Claude Code from ArcBlock/agent-skills. It costs 0 tokens per session (3,420 once invoked), scanned A, a copy of add-hook, MIT.

A command that adds a hook, an automated action tied to an event in the coding agent's lifecycle, to a plugin configuration.

In plain words
What is it for?
Use it to add or update hooks for events like before or after a tool runs, when a session starts or ends, or when a user submits a prompt.
Why use it?
It avoids manually editing configuration files and reduces mistakes when connecting actions to events such as tool use or session start.

Command for Claude Code

Written for Claude Code: argument-hint in frontmatter. Also seen: mentions .claude-plugin; mentions subagents; positional $N argument.

Not installable: its command points at a path on the author’s own machine, so it runs nowhere else. The line is /Users/you/plugin/scripts/.

Part of the plugin-development plugin — 1 skill, 7 commands, 1 agent shipped together

Good fit Use it to add or update hooks for events like before or after a tool runs, when a session starts or ends, or when a user submits a prompt.

Compare 6 commands from other repositories ↓
Install

Getting it into your agent

This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.

Claude Code
/plugin marketplace add ArcBlock/agent-skills
Claude Code
/plugin install plugin-development

Made for: Claude Code.

Or install plugin-development, the plugin that ships this one along with the rest of its 1 skill, 7 commands, 1 agent.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for add-hook

README.md
[![agentmods](https://agentmods.dev/badge/commands/arcblock/agent-skills/add-hook/github.svg)](https://agentmods.dev/commands/arcblock/agent-skills/add-hook)
Your own site
<a href="https://agentmods.dev/commands/arcblock/agent-skills/add-hook"><img src="https://agentmods.dev/badge/commands/arcblock/agent-skills/add-hook/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for add-hook

Your own site · 80×15
<a href="https://agentmods.dev/commands/arcblock/agent-skills/add-hook"><img src="https://agentmods.dev/badge/commands/arcblock/agent-skills/add-hook.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 0 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 3,420 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 98% copy Near-identical to another mod 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 5.1 $0.00000 $0.03420
Opus 5.5 $0.00000 $0.01368
Sonnet 5.5 $0.00000 $0.00684
Haiku 4.5 $0.00000 $0.00342

Measured 1mo ago against content hash 9d83c53e0ebb, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, 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 1mo 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

This is a copy

98% identical to add-hook — 4 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

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. 1mo ago First seen · 452 lines · 0 tokens per session scan A 9d83c53e0ebb

Subscribe to this mod's changes

add-hook is a command published in the GitHub repository ArcBlock/agent-skills (5 stars, last pushed 9d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 3,420 tokens. A static security scan graded it A with 0 findings. It is 98% identical to add-hook, differing in 4 lines, and is treated as a copy.