Directly invoke a tool on one of the user's registered MCP servers by connection_id. Use this for one-off tool calls without activating the full server in this session. For repeated use, prefer activate_mcp so tools appear directly in the tool list as <server>__<tool>.
Part of the Clevername server.
Free to start. No card required.
AI agents invoke call_mcp_tool to trigger processes or run actions in Clevername. Execute operations can have side effects beyond the immediate call -- triggering builds, sending notifications, or starting workflows. Rate limits and argument validation are essential to prevent runaway execution.
call_mcp_tool can trigger processes with real-world consequences. An uncontrolled agent might start dozens of builds, send mass notifications, or kick off expensive compute jobs. PolicyLayer enforces rate limits and validates arguments to keep execution within safe bounds.
Execute tools trigger processes. Rate-limit and validate arguments to prevent unintended side effects.
{
"version": "1",
"default": "deny",
"tools": {
"call_mcp_tool": {
"limits": [
{
"counter": "call_mcp_tool_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}See the full Clevername policy for all 67 tools.
These attack patterns abuse exactly the kind of access call_mcp_tool gives an agent. Each links to the full case and the policy that stops it:
Other execute tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Directly invoke a tool on one of the user's registered MCP servers by connection_id. Use this for one-off tool calls without activating the full server in this session. For repeated use, prefer activate_mcp so tools appear directly in the tool list as <server>__<tool>.. It is categorised as a Execute tool in the Clevername MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Clevername MCP server in PolicyLayer and add a rule for call_mcp_tool: 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 Clevername. Nothing to install.
call_mcp_tool is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the call_mcp_tool 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 call_mcp_tool. 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.
call_mcp_tool is provided by the Clevername MCP server (@clevername/clevername-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 67 Clevername tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
4,600+ MCP servers and 31,000+ tools scanned and risk-classified.