shunting_yard
Convert an infix math expression to postfix (RPN) and evaluate it.
This record as markdown: /tools/io-github-malamutemayhem-unclick-mcp-server/shunting-yard.md
What shunting_yard does on UnClick
AI agents invoke shunting_yard to trigger actions in UnClick. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.
| Parameter | Type | Required | Description |
|---|---|---|---|
expression | string | Yes | Infix math expression (e.g. '3 + 4 * 2') |
Parameters from the server's own tool schema.
Why shunting_yard is rated High
The tool doesn't just parse or transform; it also evaluates the expression, meaning it executes computation based on arbitrary input. However, it appears limited to math expressions, so the blast radius is low — it cannot access files, network, or system resources. Categorized as Execute because it runs/evaluates code-like input rather than simply reading or writing stored data.
From the tool's definition 'Convert an infix math expression to postfix (RPN) and evaluate it' — the tool evaluates/executes a mathematical expression
Risk signalsAccepts freeform code/query input (expression)
Attacks that exploit this kind of access
The rule that runs shunting_yard 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 shunting_yard, this is the rule to start with:
shunting_yard stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. 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 shunting_yard call is checked against it from then on.
Questions about shunting_yard
Convert an infix math expression to postfix (RPN) and evaluate it. It is categorised as a Execute tool in the UnClick MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
shunting_yard accepts 1 parameter: expression. Required: expression. 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 shunting_yard: 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.
shunting_yard is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the shunting_yard 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 shunting_yard. 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.
shunting_yard 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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