Expand a search topic with MeSH terms and synonyms.
AI agents call expand_search_terms to retrieve information from Pubmed Search without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries and returns MeSH (Medical Subject Headings) terms and synonyms related to a search topic. It is purely informational—it retrieves data without side effects. The operation is read-only, with no ability to modify, delete, or execute external operations. The low severity reflects minimal risk even in misuse, as expansion of search terms cannot harm data or systems.
From the tool's definition Tool name 'expand_search_terms' and description 'Expand a search topic with MeSH terms and synonyms' indicate retrieval and enumeration of controlled vocabulary terms. No modification, deletion, execution, or financial operations are described.
Documented attack patterns abuse exactly the kind of access expand_search_terms gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Pubmed Search, and nothing reaches the server without passing your rules. This is the rule we recommend for expand_search_terms:
{
"version": "1",
"default": "deny",
"tools": {
"expand_search_terms": {}
}
}expand_search_terms is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Expand a search topic with MeSH terms and synonyms. It is categorised as a Read tool in the Pubmed Search MCP Server, which means it retrieves data without modifying state.
Register the Pubmed Search MCP server in PolicyLayer and add a rule for expand_search_terms: 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 Pubmed Search. Nothing to install.
expand_search_terms 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 expand_search_terms 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 expand_search_terms. 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.
expand_search_terms is provided by the Pubmed Search MCP server (u9401066/pubmed-search-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Pubmed Search, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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63 Pubmed Search tools catalogued and risk-classified — across an index of 43,000+ MCP servers.