Letter Hooker

Q: What is a Claude Code skill and how does the Letter Hooker skill fit in?

A Claude Code skill is a SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. Letter Hooker is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Security category. Learn more at https://claudskills.com/learn/what-is-skill-md/.

Category: Security · Sub-category: security-misc · Last updated: 2026-07-31

ai:gemini type:integration

Extends automation-self-care with Letter Hooks, Preflight Bootloaders, Document Traversal Rules, and Self-Healing Prompt Context Enrichment for AI agents and CLIs that lack native, event-driven JSON lifecycle hooks (such as Antigravity / Gemini CLI). Use when an agent needs to inject preflight rules, search memory/gardener before work begins, enforce directory document reading strategies (CLAUDE.md / AGENTS.md), or dynamically route sidecar tasks to skills and security protocols.

Security AStatic scan found no risk patternsHow grading works ›

About this skill (catalog notes)

Letter Hooker includes at least one code block. The SKILL.md is on the shorter side at about 288 words.

Source: github.com/ellmos-ai/skills
License: MIT
Original author: Lukas Geiger + Gemini (Antigravity)
Indexed lastmod: 2026-07-31
Catalog position: Security · security-misc
Indexed related skills: 10

How Letter Hooker fits the catalog

Letter Hooker sits in the Security category under the security-misc sub-topic in the ClaudSkills catalog. There are 10 related skills indexed alongside it; comparing a few before installing usually reveals which fits your workflow best.

These notes are auto-generated from features detected in the SKILL.md file and from this catalog's structure — they aren't part of the source repository.

From the source SKILL.md

The Letter-Hooker skill extends automation-self-care for AI agent frameworks (like Antigravity / Gemini CLI) that do not possess native, event-driven JSON lifecycle hook loaders (e.g. ~/.claude/settings.json or ~/.codex/hooks.json).

What this skill does

Letter Hooker is a community-contributed Claude Code skill in the security-misc sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/letter-hooker/ and loads when your prompt matches the skill's trigger.

When to invoke it: Use when an agent needs to inject preflight rules, search memory/gardener before work begins, enforce directory document reading strategies (CLAUDE.md / AGENTS.

Who uses this skill

The Letter Hooker Claude Code skill is built for security engineers, penetration testers, DevSecOps practitioners, and development teams hardening codebases and infrastructure. It's part of ClaudSkills (also referred to as Claude Skills or Claude Code Skills) — the open community-curated registry of 191,000+ SKILL.md files for Anthropic's Claude Code agent and the wider Claude ecosystem (Claude API, Claude Agent SDK).

How to install

Free

Manual install (2 steps)

mkdir -p ~/.claude/skills/letter-hooker
curl -L https://claudskills.com/skills/letter-hooker/SKILL.md \
  -o ~/.claude/skills/letter-hooker/SKILL.md

Or just download SKILL.md directly and drop it into ~/.claude/skills/letter-hooker/. Claude Code auto-discovers it on next session.

Skills live at ~/.claude/skills/letter-hooker/SKILL.md on macOS/Linux, or %USERPROFILE%\.claude\skills\letter-hooker\SKILL.md on Windows. See the full install guide for step-by-step instructions.

📱 Install from your phone or desktop Telegram

Open @claudskills_bot on Telegram, tap Open Desktop App, and the desktop app installs this skill for you. Or share the bot link with a colleague — they get the same one-tap install. Learn more →

Pro

One-click install via the desktop app

The ClaudSkills desktop app installs any skill directly into ~/.claude/skills/ with one click — no terminal required. Pro starts at $9/mo or $149 lifetime.

Pro

For the full experience including quality scoring and one-click install features for each skill — upgrade to Pro.

See pricing → Download desktop app

Frequently asked questions

How do I install the Letter Hooker Claude Code skill?

Install via the ClaudSkills desktop app (one click) or copy SKILL.md from the source repository to ~/.claude/skills/letter-hooker/SKILL.md and restart Claude Code. Both flows are detailed at claudskills.com/install/.

What does the Letter Hooker skill do?

Is this skill free to install?

Yes. ClaudSkills is an open registry — every skill keeps its source repository's license, and manual install via copy is free. ClaudSkills Pro ($9/mo, $79/yr, or $149 one-time) adds one-click install via the desktop app and a multi-signal Quality Score.

When should I use the Letter Hooker skill?

Use Letter Hooker when your Claude Code task falls under the Security category — specifically in the security misc area. Claude Code auto-discovers installed skills and invokes the right one based on the task description, so you can also ask Claude directly (e.g. "use Letter Hooker" or describe the task and let Claude pick). Browse related skills at /category/security/.

What is a Claude Code skill and how does the Letter Hooker skill fit in?

A Claude Code skill is a SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. Letter Hooker is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Security category. Learn more at /learn/what-is-a-claude-skill/.

Attribution & license

Source: https://github.com/ellmos-ai/skills/blob/HEAD/skills/infrastructure/letter-hooker/SKILL.md
License: MIT
Author: Lukas Geiger + Gemini (Antigravity)
Website: https://github.com/ellmos-ai/skills#readme

Cite this skill

If you reference this skill in a blog post, paper, or documentation, you can cite it as:

APA

Lukas Geiger + Gemini (Antigravity). (2026). Letter Hooker [Claude Code skill]. ClaudSkills. https://claudskills.com/skills/letter-hooker/

BibTeX

@misc{letter-hooker-2026,
  author    = {Lukas Geiger + Gemini (Antigravity)},
  title     = {Letter Hooker [Claude Code skill]},
  year      = {2026},
  publisher = {ClaudSkills},
  url       = {https://claudskills.com/skills/letter-hooker/}
}

Embed this skill

Promote, attribute, or link this skill from your own README, blog post, or documentation. All three snippets are free to use — no sign-up, no API key. More distribution surfaces →

Badge

[![ClaudSkills](https://claudskills.com/badge/letter-hooker.svg)](https://claudskills.com/skills/letter-hooker/?utm_source=badge&utm_medium=readme&utm_campaign=skill_badge)

Security scan

Grade A · scanned 2026-08-26 — free static scan against the OWASP Agentic Skills Top 10.

No risk patterns were found in any of the ten OWASP-aligned categories. How grading works ›

✓ Prompt injection
✓ Data exfiltration
✓ Supply chain
✓ Reverse shell
✓ Credentials
✓ Execution
✓ Filesystem
✓ Persistence
✓ Obfuscation
✓ Network

Show this grade on your repo (click to copy):

[![Security: A](https://img.shields.io/badge/Security-A-2e7d32)](https://claudskills.com/skills/letter-hooker/#security)

More Security skills

Browse all Security skills in the ClaudSkills registry, or explore these other picks from the same category:

Browse all Security skills → Top 100 skills

Part of ClaudSkills — the open registry for Claude Skills & Claude Code Skills. · What's New · Install guide · About · llms.txt

Part of Acreator Store — Adam Lankamer's AI tools: PerfectStudio · Ucaption · UTagger · AutoXPoster · TestYourSkills · AutomationFlows · Au Naturel · Telegram @acreatorstore