set_parameter_expression

Set one or more parameters on a node to an expression, bind expression, or constant value without needing the raw-Python escape hatch. Supports five modes:

SERVERAos SOURCE@hybridlabor-api/aos

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/hybridlabor-api-aos/set-parameter-expression.md

WHAT IT DOES

What set_parameter_expression does on Aos

AI agents use set_parameter_expression to create or update resources in Aos, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Aos environment.

RISK

Why set_parameter_expression is rated Medium

Modifies node parameters reversibly via expression binding or constant values. No permanent deletion, but affects node behavior.

From the tool's definition Set one or more parameters on a node to an expression, bind expression, or constant value

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs set_parameter_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 set_parameter_expression, this is the rule to start with:

set_parameter_expression Rate-limited

set_parameter_expression stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_parameter_expression": {
      "limits": [
        {
          "counter": "set_parameter_expression_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Aos, apply this rule, and every set_parameter_expression call is checked against it from then on.

FAQ

Questions about set_parameter_expression

What does the set_parameter_expression tool do? +

Set one or more parameters on a node to an expression, bind expression, or constant value without needing the raw-Python escape hatch. Supports five modes:. It is categorised as a Write tool in the Aos MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_parameter_expression? +

Register the Aos MCP server in PolicyLayer and add a rule for set_parameter_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.

What risk level is set_parameter_expression? +

set_parameter_expression is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit set_parameter_expression? +

Yes. Add a rate_limit block to the set_parameter_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.

How do I block set_parameter_expression completely? +

Set action: deny in the PolicyLayer policy for set_parameter_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.

What MCP server provides set_parameter_expression? +

set_parameter_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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