AI agents use add_design_day to create or update resources in Openstudio — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Openstudio environment.
Design day creation modifies the simulation model state reversibly by adding weather/climate data parameters for EnergyPlus analysis. This is a Write operation—it creates new model configuration that can be deleted or edited, but does not execute simulations or permanently destroy data.
From the tool's definition Tool name 'add_design_day' indicates creation of a design day object in OpenStudio building energy simulation. The 'add_' prefix pattern is consistent with sibling tools (add_air_loop, add_baseline_system, add_doas_system, etc.) that modify simulation models.
Documented attack patterns abuse exactly the kind of access add_design_day gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Openstudio, and nothing reaches the server without passing your rules. This is the rule we recommend for add_design_day:
{
"version": "1",
"default": "deny",
"tools": {
"add_design_day": {
"limits": [
{
"counter": "add_design_day_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_design_day 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.
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add_design_day. It is categorised as a Write tool in the Openstudio MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Openstudio MCP server in PolicyLayer and add a rule for add_design_day: 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 Openstudio. Nothing to install.
add_design_day is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the add_design_day 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 add_design_day. 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.
add_design_day is provided by the Openstudio MCP server (natlabrockies/openstudio-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Openstudio, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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146 Openstudio tools catalogued and risk-classified — across an index of 43,000+ MCP servers.