AI agents call filter_blobs_by_size to retrieve information from Gcp Storage without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries metadata (blob sizes) and returns a filtered list. It has no side effects: it does not create, modify, delete, or execute operations. The operation is purely informational, making it a Read category tool with low severity, as misuse would only expose information rather than cause data loss or operational impact.
From the tool's definition Tool description states 'Filter blobs by size range' — a query operation that retrieves or filters existing data with no modification or deletion. The verb 'filter' indicates data retrieval/inspection only.
Documented attack patterns abuse exactly the kind of access filter_blobs_by_size gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Gcp Storage, and nothing reaches the server without passing your rules. This is the rule we recommend for filter_blobs_by_size:
{
"version": "1",
"default": "deny",
"tools": {
"filter_blobs_by_size": {}
}
}filter_blobs_by_size is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Filter blobs by size range. It is categorised as a Read tool in the Gcp Storage MCP Server, which means it retrieves data without modifying state.
Register the Gcp Storage MCP server in PolicyLayer and add a rule for filter_blobs_by_size: 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 Storage. Nothing to install.
filter_blobs_by_size 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 filter_blobs_by_size 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 filter_blobs_by_size. 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.
filter_blobs_by_size is provided by the Gcp Storage MCP server (uysalserkan/gcp-storage-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Gcp Storage, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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23 Gcp Storage tools catalogued and risk-classified — across an index of 43,000+ MCP servers.