AI agents call hybrid_search_tool to retrieve information from Brain without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
A hybrid search tool on a note-taking system retrieves or queries stored Markdown notes without modifying data. It fits the 'Read' category as it performs queries with no side effects. The empty description lowers confidence slightly, but the name and context of sibling read tools (keyword_search, semantic_search) and the 'hybrid search' pattern in note applications all point to data retrieval.
From the tool's definition Tool name 'hybrid_search_tool' combined with sibling tools that include 'keyword_search_tool' and 'semantic_search_tool' indicates a search/query function.
Documented attack patterns abuse exactly the kind of access hybrid_search_tool gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Brain, and nothing reaches the server without passing your rules. This is the rule we recommend for hybrid_search_tool:
{
"version": "1",
"default": "deny",
"tools": {
"hybrid_search_tool": {}
}
}hybrid_search_tool is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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hybrid_search_tool. It is categorised as a Read tool in the Brain MCP Server, which means it retrieves data without modifying state.
Register the Brain MCP server in PolicyLayer and add a rule for hybrid_search_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 Brain. Nothing to install.
hybrid_search_tool 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 hybrid_search_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 hybrid_search_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.
hybrid_search_tool is provided by the Brain MCP server (irahulstomar/brain-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Brain, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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10 Brain tools catalogued and risk-classified — across an index of 43,000+ MCP servers.