---
title: "Skill: Overview"
summary: A set of instructions that changes how your agent spends tokens. No runtime, no proxy.
canonical: https://docs.caveman.so/docs/skill
layer: skill
license: MIT
capability: skill
updated: 2026-08-26T03:57:26+02:00
basis: inferred
---

# Skill: Overview

> A set of instructions that changes how your agent spends tokens. No runtime, no proxy.
<DocSchema slug="skill" />

The skill is the cheapest layer in the stack because it is not software. It is a file your agent reads,
and it changes how the agent writes for the rest of the session.

- What it is: One Markdown instruction file, plus optional commands and subagent presets.
- Runtime: None. No process, no port, no config file.
- Account: Not required.
- Licence: MIT.
- Install: `npx skills add JuliusBrussee/caveman`

## Install

```bash
npx skills add JuliusBrussee/caveman
```

Without `-g` this writes into `./.agents/skills` under your current directory rather than a global
location. Several agents have their own native path:

```bash
# Claude Code
claude plugin marketplace add JuliusBrussee/caveman
claude plugin install caveman@caveman

# Gemini CLI
gemini extensions install https://github.com/JuliusBrussee/caveman

# Codex CLI
npx skills add JuliusBrussee/caveman -a codex

# Cursor, which needs -g
npx skills add JuliusBrussee/caveman -a cursor -g

# opencode
npx -y github:JuliusBrussee/caveman -- --only opencode
```

There is also a full installer that wires up hooks and a status line for Claude Code. It is pinned to a
tag, it is safe to re-run, and it supports `--dry-run`.

```bash
curl -fsSL https://raw.githubusercontent.com/JuliusBrussee/caveman/v2.3.1/install.sh | bash
```

```powershell
irm https://raw.githubusercontent.com/JuliusBrussee/caveman/v2.3.1/install.ps1 | iex
```

## What it removes

Articles, filler, pleasantries, hedging and tool-call narration. Sentence fragments are allowed.
Decorative tables and emoji are not.

## What it will not touch

This list is the reason the skill is safe to leave on.

- Code blocks, verbatim
- Function, method and API names
- CLI commands and flags
- Commit type keywords
- Exact error strings
- The language you are writing in

It also refuses to invent abbreviations. `cfg`, `impl`, `req`, `res` and `fn` are banned, and so are
arrow characters standing in for words. The reason is measurable rather than stylistic: the tokenizer
splits those the same way it splits the full word, so the abbreviation saves nothing and costs clarity.

## When it steps aside

The skill drops out of terse mode on its own for:

- Security warnings
- Confirmations of anything irreversible
- Ambiguous multi-step sequences
- Any case where compressing the answer would create the ambiguity

## Levels

```text
/caveman lite
/caveman full          # default
/caveman ultra
/caveman wenyan-lite
/caveman wenyan-full
/caveman wenyan-ultra
/caveman off
```

`off`, "stop caveman" and "normal mode" all do the same thing.

## What else comes with it

One install also brings a set of commands and work-pattern skills.

- Commands: `/caveman-commit · /caveman-review · /caveman-compress · /caveman-stats · /caveman-help`
- Subagent presets: cavecrew-investigator, cavecrew-builder, cavecrew-reviewer
- Work patterns: investigate-first, lean-build, surgical-patch, safe-refactor, migration, verify-and-stop

## What it saves

On the committed benchmark suite of ten prompts, output tokens drop by about 65 percent on average, with
a range of 22 to 87 percent. That is a per-run inferred estimate measured on that suite. It is not a
promise about your bill, and it covers output tokens only.

The range matters more than the average here. A tightly scoped refactor prompt saved 22 percent. A long
explanatory answer saved 87 percent. Which end you land on depends on how much of your traffic is prose.