AI agents call search_by_subject to retrieve information from BnF API Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool retrieves or queries data from the Gallica library without modifying, deleting, or executing code. It is part of a suite of search tools designed for discovery and research in a digital library. The empty description prevents absolute certainty, but the consistent naming pattern and server purpose strongly indicate a read-only search operation with minimal blast radius if misused.
From the tool's definition Tool name 'search_by_subject' indicates a search operation. Server description emphasizes 'search the Gallica digital library' and lists sibling tools all prefixed with 'search_' (advanced_search, natural_language_search, search_by_author, etc.), confirming…
Documented attack patterns abuse exactly the kind of access search_by_subject gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and BnF API Server, and nothing reaches the server without passing your rules. This is the rule we recommend for search_by_subject:
{
"version": "1",
"default": "deny",
"tools": {
"search_by_subject": {}
}
}search_by_subject is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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search_by_subject. It is categorised as a Read tool in the BnF API Server MCP Server, which means it retrieves data without modifying state.
Register the BnF API Server MCP server in PolicyLayer and add a rule for search_by_subject: 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 BnF API Server. Nothing to install.
search_by_subject 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 search_by_subject 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 search_by_subject. 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.
search_by_subject is provided by the BnF API Server MCP server (kryzo/mcp-bibliotheque_nationale_de_france). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from BnF API 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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8 BnF API Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.