What is hook-authoring?

Instructions for writing hook definitions in `.ai/hooks.toml`, a TOML configuration file. Hooks are actions that run before or after an AI tool is used, when a session changes, or at other supported events.

Use it when creating or editing hook files, choosing events and matchers, and checking how one hook definition maps to different AI tools.

It explains the allowed event names and matching rules, including which events work across Claude Code and Cursor. This reduces mistakes when creating hooks that must be translated between tools.

hook-authoring — Skill for Claude Code by TheThoughtagen/agentsync

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.

Any agent

npx skills add TheThoughtagen/agentsync --skill hook-authoring

Clone the repo

git clone --depth 1 https://github.com/TheThoughtagen/agentsync

Made for: Claude Code.

Or install aisync, the plugin that ships this one along with the rest of its 2 skills, 7 commands, 2 hooks.

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/thethoughtagen/agentsync/hook-authoring/github.svg)](https://agentmods.dev/skills/thethoughtagen/agentsync/hook-authoring)

Your own site

<a href="https://agentmods.dev/skills/thethoughtagen/agentsync/hook-authoring"><img src="https://agentmods.dev/badge/skills/thethoughtagen/agentsync/hook-authoring/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/thethoughtagen/agentsync/hook-authoring"><img src="https://agentmods.dev/badge/skills/thethoughtagen/agentsync/hook-authoring.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 35 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,137 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 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.

Model	Per session	Once invoked
Fable 5.1	$0.00035	$0.01137
Opus 5.5	$0.00014	$0.00455
Sonnet 5.5	$0.00007	$0.00227
Haiku 4.5	$0.00003	$0.00114

Measured 2mo ago against content hash 9e2c9d74a17a, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

hook-authoring 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 2mo 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.

plugins/aisync/skills/hook-authoring/SKILL.md · 137 lines

How it starts

The opening of the file, as written. The whole thing — 137 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Hook Authoring Guide

File Format

Hooks are defined in .ai/hooks.toml using TOML. Each hook is grouped under an [[EventName]] section with an optional matcher field, and contains one or more [[EventName.hooks]] entries.

[[PreToolUse]]
matcher = "Bash"

[[PreToolUse.hooks]]
type = "command"
command = "bash .ai/scripts/validate-bash.sh"
timeout = 10

Valid Events

Shared Events (work in both Claude Code and Cursor via aisync translation)

Event	Description
`PreToolUse`	Fires before a tool is invoked. Use `matcher` to target specific tools.
`PostToolUse`	Fires after a tool completes. Use `matcher` to target specific tools.
`Stop`	Fires when the agent stops (completes a response).
`SubagentStop`	Fires when a sub-agent stops.

Claude Code Only (via aisync translation)

Event	Description
`Notification`	Fires when a notification is sent.

Cursor Only (via aisync translation)

Event	Description
`PostToolUseFailure`	Fires when a tool invocation fails.
`SessionStart`	Fires when a new session begins.
`SessionEnd`	Fires when a session ends.
`BeforeShellExecution`	Fires before a shell command runs.
`AfterShellExecution`	Fires after a shell command completes.
`BeforeReadFile`	Fires before reading a file.
`AfterFileEdit`	Fires after a file is edited.
`BeforeSubmitPrompt`	Fires before a prompt is submitted.
`PreCompact`	Fires before context compaction.
`AfterAgentResponse`	Fires after the agent responds.
`AfterAgentThought`	Fires after an agent thought step.
`SubagentStart`	Fires when a sub-agent starts.
`BeforeMCPExecution`	Fires before an MCP tool call.
`AfterMCPExecution`	Fires after an MCP tool call completes.

Note: Claude Code natively supports additional events (SessionStart, SessionEnd, UserPromptSubmit, PreCompact) that aisync does not yet translate. When writing hooks for these events in .ai/hooks.toml, aisync will currently skip them during Claude Code translation. To use these events, configure them directly in .claude/settings.json or via a Claude Code plugin's hooks.json.

Read the full file on GitHub · 137 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.

2mo ago First seen · 137 lines · 35 tokens per session scan A 9e2c9d74a17a

Subscribe to this mod's changes

hook-authoring is a skill published in the GitHub repository TheThoughtagen/agentsync (2 stars, last pushed 7mo ago), licensed MIT. It adds 35 tokens to every session and 1,137 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-08-31.

Building agents ai-agents

hook-authoring next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
hook-authoringTheThoughtagen/agentsync	Skill	2	7mo ago	MIT	A	35	Claude Code
imagegenopenai/codex	Skill	134k	today	Apache-2.0	A	113	Codex
local-ai-agentsmicrosoft/ai-agents-for-beginners	Skill	79k	today	MIT	A	200	Claude Code, Codex
playwright-climicrosoft/playwright	Skill	99k	today	Apache-2.0	A	19	Claude Code
systematic-debuggingobra/superpowers	Skill	314k	3d ago	MIT	A	21	Claude Code
next-cache-components-adoptionvercel/next.js	Skill	143k	today	MIT	A	95	Claude Code
chat-pet-sprite-creationmicrosoft/vscode	Skill	195k	today	MIT	A	53	Claude Code, Codex