opencode-caveman

OpenCode plugin that injects caveman compression rules into every session — automatically, without manual activation.

Full credit: This plugin is a direct adaptation of caveman by Julius Brussee (52k+ stars). All compression rules, intensity levels, and the core philosophy — "why use many token when few token do trick" — originate from that project. This repo only packages those rules for the OpenCode plugin system.

How it works

Three layers, each strengthening the last:

Layer	File	Mechanism
Always-on rules	`AGENTS.md`	Loaded into system prompt at session init. Survives `/clear`.
Per-turn enforcement	`index.ts` → `experimental.chat.system.transform`	Rules injected into every LLM call. Model sees them every turn — no drift.
Compaction survival	`index.ts` → `experimental.session.compacting`	Rules injected into compaction prompt context. Model's summary includes caveman state — survives `/compact`.
Live mode switching	`index.ts` → `command.execute.before` + `caveman_set_level` tool	`/caveman` commands intercepted before reaching model. Mode written to `~/.config/opencode/.caveman-active` — persists across sessions.
On-demand skill	`skills/caveman/SKILL.md`	Loadable via skill picker for intensity switching docs.

This mirrors how the original caveman works in Claude Code: SessionStart hook injects rules as hidden system context; UserPromptSubmit hook re-injects a small reminder every turn; flag file persists mode across sessions.

Install

Option A — plugin (full enforcement, recommended)

Build and copy to OpenCode's global plugin directory:

cd opencode-caveman
bun install
bun run build
cp .opencode/plugins/caveman.js ~/.config/opencode/plugins/caveman.js

Or reference from ~/.config/opencode/opencode.json:

{
  "plugin": ["@mumme-it/opencode-caveman"]
}

Option B — AGENTS.md only (no code, simpler)

Copy AGENTS.md globally:

cp AGENTS.md ~/.config/opencode/AGENTS.md

Add to ~/.config/opencode/opencode.json:

{
  "instructions": ["AGENTS.md"]
}

Rules load at session start. No per-turn enforcement or compaction survival.

Option C — skill only (on-demand)

cp -r skills/caveman ~/.config/opencode/skills/caveman

Activate per-session: ctrl+p → Load Skill → caveman.

Modes

Command	Effect
`/caveman`	Activate full mode
`/caveman lite`	No filler. Articles kept. Professional but tight.
`/caveman full`	Drop articles, fragments OK. Classic caveman. (default)
`/caveman ultra`	Max compression. Prose abbreviations, arrows for causality.
`stop caveman`	Return to normal mode.

Mode persists across sessions via ~/.config/opencode/.caveman-active.

Credit


Original	caveman
Author	Julius Brussee
Stars	52k+
Philosophy	why use many token when few token do trick
Benchmarked savings	~65% output token reduction (range 22–87%)
Accuracy	100% — technical substance preserved