Return the full classical sources for a hexagram by its number (1–64): judgment (卦辞), image (大象), Tuan commentary, Zhu Xi 周易本义, Yang Tian Cai modern explanation, plain-language 白话, and historical anecdote — in both Chinese and English.
Part of the Yarrow server.
Free to start. No card required.
AI agents call lookup_hexagram to retrieve information from Yarrow without modifying any data. This is common in research, monitoring, and reporting workflows where the agent needs context before taking action. Because read operations don't change state, they are generally safe to allow without restrictions -- but you may still want rate limits to control API costs.
Even though lookup_hexagram only reads data, uncontrolled read access can leak sensitive information or rack up API costs. An agent caught in a retry loop could make thousands of calls per minute. A rate limit gives you a safety net without blocking legitimate use.
Read-only tools are safe to allow by default. No rate limit needed unless you want to control costs.
{
"version": "1",
"default": "deny",
"tools": {
"lookup_hexagram": {}
}
}See the full Yarrow policy for all 3 tools.
These attack patterns abuse exactly the kind of access lookup_hexagram gives an agent. Each links to the full case and the policy that stops it:
Other read tools across the catalogue. The same approach applies to each: allow, with a rate cap to control cost.
Return the full classical sources for a hexagram by its number (1–64): judgment (卦辞), image (大象), Tuan commentary, Zhu Xi 周易本义, Yang Tian Cai modern explanation, plain-language 白话, and historical anecdote — in both Chinese and English.. It is categorised as a Read tool in the Yarrow MCP Server, which means it retrieves data without modifying state.
Register the Yarrow MCP server in PolicyLayer and add a rule for lookup_hexagram: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Yarrow. Nothing to install.
lookup_hexagram is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the lookup_hexagram rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for lookup_hexagram. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
lookup_hexagram is provided by the Yarrow MCP server (https://yarrow-oracle.shaozhengkun.workers.dev/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 3 Yarrow tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
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