AI agents call count_values to retrieve information from FiftyOne 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 and aggregates statistics about field values in a computer vision dataset. It performs a read-only operation that queries data without creating, modifying, deleting, or executing external code. The operation has minimal blast radius—worst case, it returns unexpected statistical results but cannot harm the underlying dataset or trigger unintended side effects.
From the tool's definition Tool name 'count_values' and description 'Count occurrences of each value for a field' indicate aggregation/querying of existing data with no modification or deletion capabilities.
Documented attack patterns abuse exactly the kind of access count_values gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and FiftyOne MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for count_values:
{
"version": "1",
"default": "deny",
"tools": {
"count_values": {}
}
}count_values is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Count occurrences of each value for a field. It is categorised as a Read tool in the FiftyOne MCP Server MCP Server, which means it retrieves data without modifying state.
Register the FiftyOne MCP Server MCP server in PolicyLayer and add a rule for count_values: 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 FiftyOne MCP Server. Nothing to install.
count_values 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 count_values 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 count_values. 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.
count_values is provided by the FiftyOne MCP Server MCP server (voxel51/fiftyone-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from FiftyOne MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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47 FiftyOne MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.