opencode-slim-system

Replaces OpenCode's default system prompt and built-in tool descriptions with short, token-efficient alternatives. No behavioral changes — only prose length.

How it works

Two hooks registered into OpenCode's plugin system:

experimental.chat.system.transform — detects the bundled system prompt (by recognizable markers) and swaps it for prompt/default.txt. Everything after the env block (model, directory, date, skills, AGENTS.md instructions) is preserved.
tool.definition — fires for every tool during schema construction. If a slim description exists in tool/<id>.txt, it replaces the verbose original. Tool schemas and execution behavior are unchanged.

Token savings

Component	Before	After	Savings
System prompt (provider text)	~1,800 tokens	~240 tokens	~1,560
Tool descriptions (18 built-in)	~9,500 tokens	~750 tokens	~8,750
Total per request	~11,300 tokens	~990 tokens	~10,310

Tool descriptions are NOT cacheable — they are sent on every LLM turn. System prompt text IS cacheable (Anthropic prompt caching, OpenAI cached prefix), so the tool description savings compound on every single message.

Installation

Load as an npm plugin in opencode.json:

{
  "plugin": ["opencode-slim-system"]
}

Or as a local plugin — clone into ~/.config/opencode/plugins/opencode-slim-system/.

Customisation

System prompt: edit prompt/default.txt.
Tool descriptions: edit any file in tool/ matching the tool ID (e.g. tool/bash.txt, tool/read.txt).

The plugin scans the tool/ directory at startup, so new .txt files are picked up automatically.

Inspired by

AnthonyFangqing/opencode-special-edition — the original minimal-prompt plugin. This fork extracts the same approach into an independent, published package with updated tool coverage.
PR #24202 — MartinWie's condensed tool descriptions (unmerged).

License

MIT