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Open Caveman
00What the agent does before it calls out/MIT

Skill

A set of instructions that changes how your agent spends tokens. No runtime, no proxy.

View as Markdown

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#

terminal
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:

terminal
# 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.

terminal
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.