fleet_list_custom_variables
AI agents call fleet_list_custom_variables to retrieve information from Fleet without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The 'list' verb is characteristic of Read operations that query and return data without side effects. No description is provided, but the tool naming convention and context of other tools on the server (which include destructive operations like 'fleet_cancel_batch_script' and 'fleet_delete_bootstrap_package') suggest this tool performs simple enumeration of existing custom variables.
From the tool's definition Tool name 'fleet_list_custom_variables' with 'list' verb indicates data retrieval with no modification capability. Related sibling tools include create, delete, and batch operations, confirming this is the read counterpart.
Documented attack patterns abuse exactly the kind of access fleet_list_custom_variables 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_list_custom_variables:
{
"version": "1",
"default": "deny",
"tools": {
"fleet_list_custom_variables": {}
}
}fleet_list_custom_variables is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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fleet_list_custom_variables. It is categorised as a Read tool in the Fleet MCP Server, which means it retrieves data without modifying state.
Register the Fleet MCP server in PolicyLayer and add a rule for fleet_list_custom_variables: 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_list_custom_variables is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the fleet_list_custom_variables 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_list_custom_variables. 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_list_custom_variables 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.