lehmer_code
Convert between permutations and Lehmer codes, compute permutation rank and unrank.
This record as markdown: /tools/io-github-malamutemayhem-unclick-mcp-server/lehmer-code.md
What lehmer_code does on UnClick
AI agents call lehmer_code to retrieve information from UnClick without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
| Parameter | Type | Required | Description |
|---|---|---|---|
n | number | — | Permutation size for unranking (use with rank) |
rank | number | — | Lexicographic rank to decode (use with n) |
permutation | array | — | Permutation of [0..n-1] to encode |
Parameters from the server's own tool schema.
Why lehmer_code is rated Low
Lehmer code conversion and permutation ranking are stateless mathematical algorithms. The tool reads input parameters and returns computed results without creating, modifying, deleting, or executing any external operations. This is a straightforward Read-category utility with minimal security risk.
From the tool's definition Tool description states 'Convert between permutations and Lehmer codes, compute permutation rank and unrank' — these are pure mathematical computations with no side effects, data retrieval, modification, or external operations.
Attacks that exploit this kind of access
The rule that runs lehmer_code safely
PolicyLayer is an MCP gateway: it sits between your AI agents and UnClick, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For lehmer_code, this is the rule to start with:
lehmer_code is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect UnClick, apply this rule, and every lehmer_code call is checked against it from then on.
Questions about lehmer_code
Convert between permutations and Lehmer codes, compute permutation rank and unrank. It is categorised as a Read tool in the UnClick MCP Server, which means it retrieves data without modifying state.
lehmer_code accepts 3 parameters: n, rank, permutation. The full parameter table on this page comes from the server's own tool schema.
Register the UnClick MCP server in PolicyLayer and add a rule for lehmer_code: 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 UnClick. Nothing to install.
lehmer_code 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 lehmer_code 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 lehmer_code. 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.
lehmer_code is provided by the UnClick MCP server (@unclick/mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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