AI agents call fleet_delete_custom_variable to permanently remove resources in Fleet — typically in cleanup and lifecycle workflows. It does its job in a single call, and there is no undo.
The 'delete' verb in the function name indicates irreversible data destruction. Custom variables in a fleet management system are configuration entities; deleting them permanently removes that data from the system. While the description is empty, the name alone clearly signals a destructive operation. This ranks as Destructive rather than Write because deletion is not reversible without manual recovery.
From the tool's definition Tool name is 'fleet_delete_custom_variable' which contains the verb 'delete', indicating irreversible removal of data.
Documented attack patterns abuse exactly the kind of access fleet_delete_custom_variable gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Fleet, and nothing reaches the server without passing your rules. This is the rule we recommend for fleet_delete_custom_variable:
{
"version": "1",
"default": "deny",
"hide": [
"fleet_delete_custom_variable"
]
}fleet_delete_custom_variable disappears from the agent's tool list entirely, and any attempt to call it is denied. The rest of the server keeps working.
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fleet_delete_custom_variable. It is categorised as a Destructive tool in the Fleet MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.
Register the Fleet MCP server in PolicyLayer and add a rule for fleet_delete_custom_variable: 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 Fleet. Nothing to install.
fleet_delete_custom_variable is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.
Yes. Add a rate_limit block to the fleet_delete_custom_variable 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 fleet_delete_custom_variable. 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.
fleet_delete_custom_variable is provided by the Fleet MCP server (fleet-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Fleet, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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85 Fleet tools catalogued and risk-classified — across an index of 43,000+ MCP servers.