shell-builtins

shell-builtins is a skill for Claude Code, Codex from charmbracelet/crush. It costs 42 tokens per session (783 once invoked), scanned A, original, no licence file.

A skill for Crush's built-in shell, the command environment inside the coding agent. It covers commands that Crush intercepts before they run normally.

In plain words
What is it for?
Creating or changing shell built-ins in Crush's internal shell, or understanding how those commands are intercepted.
Why use it?
It explains where shell commands are handled internally and helps keep new or edited built-in commands consistent with Crush.

Skill for Claude CodeCodex

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 skills/charmbracelet/crush/shell-builtins
Any agent
npx skills add charmbracelet/crush --skill shell-builtins
Clone the repo
git clone --depth 1 https://github.com/charmbracelet/crush

Made for: Claude Code, Codex.

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 shell-builtins

README.md
[![agentmods](https://agentmods.dev/badge/skills/charmbracelet/crush/shell-builtins.svg)](https://agentmods.dev/skills/charmbracelet/crush/shell-builtins)
Your own site
<a href="https://agentmods.dev/skills/charmbracelet/crush/shell-builtins"><img src="https://agentmods.dev/badge/skills/charmbracelet/crush/shell-builtins.svg" alt="Measured on agentmods" height="20"></a>
Per session 42 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 783 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown 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 $0.00042 $0.00783
Opus 5 $0.00021 $0.00392
Sonnet 5 $0.00008 $0.00157
Haiku 4.5 $0.00004 $0.00078

Measured 5d ago against content hash cf06499c315c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

shell-builtins 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 5d 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.

.agents/skills/shell-builtins/SKILL.md · 73 lines

The source is not reproduced here

A licence we could not identify

The repository carries a LICENSE file, but it is custom or dual enough that GitHub cannot name it and neither can this catalogue. Unknown terms are not permission, so the body is not copied here. Read the licence at the source and decide for yourself.

Read it on GitHub

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. 5d ago First seen · 73 lines · 42 tokens per session scan A cf06499c315c

Subscribe to this mod's changes

shell-builtins is a skill published in the GitHub repository charmbracelet/crush (27,880 stars, last pushed yesterday), with no licence file. It adds 42 tokens to every session and 783 once invoked, about $0.0002 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.

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