Use this as the primary tool to discover the types of metrics available in a Google Cloud project. This is a good first step to understanding what data is available for monitoring and building dashboards or alerts.
AI agents call list_metric_descriptors to retrieve information from Observability without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool retrieves metadata about available metrics in a GCP project. It performs no data modification, deletion, or execution. Even if an AI agent calls this repeatedly, the worst outcome is discovering available metrics, which poses minimal risk. This is clearly a Read operation.
From the tool's definition Tool description states it is used to 'discover the types of metrics available' and to understand 'what data is available' — this is a query/list operation with no side effects.
Attacks that exploit this kind of access
Use this as the primary tool to discover the types of metrics available in a Google Cloud project. This is a good first step to understanding what data is available for monitoring and building dashboards or alerts. It is categorised as a Read tool in the Observability MCP Server, which means it retrieves data without modifying state.
Register the Observability MCP server in PolicyLayer and add a rule for list_metric_descriptors: 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 Observability. Nothing to install.
list_metric_descriptors 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 list_metric_descriptors 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 list_metric_descriptors. 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.
list_metric_descriptors is provided by the Observability MCP server (@google-cloud/observability-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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