Yarrow — An I-Ching oracle for the agent era

License: MIT

Yarrow lets you (and your agents) consult the Book of Changes — cast a hexagram, read the classical sources, and get a Wilhelm/Baynes-style reflection. Offline-first iOS app, plus a public MCP server so any LLM agent can reach the same oracle.

"The I-Ching does not predict; it mirrors. The question you bring decides the reading."

What's in this repo

Path	What
`src/`	Cloudflare Workers source — public MCP endpoint + iOS app proxy
`src/data_hexagrams.json`	64 hexagrams with bilingual classical sources (杨天才 / 朱熹 / 断易天机 / 白话题解)
`src/hexagram.ts`	Deterministic casting (coins / yarrow stalks / random), seeded by FNV-1a + mulberry32
`src/mcp.ts`	MCP JSON-RPC 2.0 handler (3 tools, 30 readings/day per anonymous caller)
`.claude-plugin/marketplace.json`	Claude Code / Codex plugin marketplace manifest
`skills/yarrow/SKILL.md`	The Yarrow skill — pluggable into any Claude Code or Codex install
`npm/yarrow-mcp/`	`@shaozhengkun/yarrow-mcp` — stdio bridge for clients that don't speak HTTP MCP
`submissions/`	Drafts for modelcontextprotocol/servers, Smithery, mcp.run
`INTEGRATIONS.md`	Copy-paste configs for Claude Code / Claude Desktop / Codex / Hermes

The iOS source lives separately at yarrow-ios (TODO).

For users

📱 iOS app

Download on the App Store → · $4.99 · iOS 17+ · no tracking, no account.

All 64 hexagrams and their classical commentary ship in the app; AI reading is optional and runs through this Worker.

🤖 Agents

Claude Code — install the plugin:

claude plugin marketplace add https://github.com/shaozhengkun123/yarrow
claude plugin install yarrow

Claude Desktop — add to ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "yarrow": { "url": "https://yarrow-oracle.shaozhengkun.workers.dev/mcp" }
  }
}

Codex CLI / Hermes / older Claude Desktop — use the stdio bridge:

npx @shaozhengkun/yarrow-mcp

Or pin it in your client's config — see INTEGRATIONS.md for every platform.

Anyone with curl —

curl -s -X POST https://yarrow-oracle.shaozhengkun.workers.dev/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{
    "name":"divine",
    "arguments":{"question":"Should I take the new job?","locale":"en"}
  }}'

The MCP tools

Tool	Purpose
`cast_hexagram`	Toss the coins / cast the stalks. Returns primary hexagram + moving lines + changing hexagram, all metadata. Deterministic if you pass `seed`.
`lookup_hexagram`	Get a hexagram's classical text — Wilhelm-style header, judgment, image, and 杨天才 / 朱熹 / 断易天机 / 白话 commentaries.
`divine`	One-shot reading: casts, looks up, and generates a Wilhelm/Baynes-style reflection grounded in the sources. 30/day per anonymous caller.

Self-hosting

This Worker is MIT — fork, deploy your own, point your agents at your URL.

git clone https://github.com/shaozhengkun123/yarrow
cd yarrow
npm install
npx wrangler login
npx wrangler kv:namespace create QUOTA          # copy id into wrangler.toml
echo -n '<your OpenAI-compatible chat URL>' | npx wrangler secret put PROXY_URL
echo -n '<your API key>'                   | npx wrangler secret put PROXY_KEY
npx wrangler deploy

Your endpoint will be https://yarrow-oracle.<your-subdomain>.workers.dev.

Boundaries

Yarrow is for reflection, not prediction. The system prompt baked into the Worker refuses:

fortune-telling / specific future predictions
medical, legal, or financial advice
requests to "reveal what will happen"

The classical voice is direct; the framing is Jungian. This is the line we draw, in the iOS app and the MCP both.

License

MIT for code; classical sources are in the public domain. See LICENSE.

Yarrow — An I-Ching oracle for the agent era