This record as markdown: /tools/hybridlabor-api-aos/evaluate-expression.md
What evaluate_expression does on Aos
AI agents invoke evaluate_expression to trigger actions in Aos. 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.
Why evaluate_expression is rated High
The name 'evaluate_expression' strongly implies execution of an arbitrary mathematical expression, which may permit execution of unintended or complex computations. Since the description is empty, exact behavior is unknown, but sibling tools suggest this evaluates math expressions. The execute category fits best given the potential for arbitrary expression evaluation.
From the tool's definition Tool name 'evaluate_expression' on a math server; description is empty and uninformative.
Attacks that exploit this kind of access
The rule that runs evaluate_expression safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Aos, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For evaluate_expression, this is the rule to start with:
evaluate_expression 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 Aos, apply this rule, and every evaluate_expression call is checked against it from then on.
Questions about evaluate_expression
evaluate_expression is a execute tool on the Aos MCP server. It is categorised as a Execute tool in the Aos MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Aos MCP server in PolicyLayer and add a rule for evaluate_expression: 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 Aos. Nothing to install.
evaluate_expression 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 evaluate_expression 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 evaluate_expression. 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.
evaluate_expression is provided by the Aos MCP server (@hybridlabor-api/aos). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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