gcp-spanner-list-instances
AI agents call gcp-spanner-list-instances to retrieve information from GCP Billing and Monitoring MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves or enumerates GCP Spanner instances, a read-only operation with no side effects. Listing resources is a foundational Read category action. Even if misused by an agent, it only exposes metadata about existing infrastructure with minimal blast radius (no data is modified, deleted, or executed). Severity is low because enumeration alone provides reconnaissance but no direct impact on systems or data.
From the tool's definition Tool name 'gcp-spanner-list-instances' indicates a listing/retrieval operation. The 'list' prefix and 'instances' object suggest querying existing Spanner database instances without modification. No description provided, which lowers confidence slightly.
Attacks that exploit this kind of access
gcp-spanner-list-instances. It is categorised as a Read tool in the GCP Billing and Monitoring MCP Server MCP Server, which means it retrieves data without modifying state.
Register the GCP Billing and Monitoring MCP Server MCP server in PolicyLayer and add a rule for gcp-spanner-list-instances: 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 GCP Billing and Monitoring MCP Server. Nothing to install.
gcp-spanner-list-instances 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 gcp-spanner-list-instances 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 gcp-spanner-list-instances. 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.
gcp-spanner-list-instances is provided by the GCP Billing and Monitoring MCP Server MCP server (radiumgu/gcp-billing-and-monitoring-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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