AI agents call search_by_doi to retrieve information from Crossref Local without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves bibliographic metadata or citation information by DOI identifier. It queries a scholarly database and returns results with no side effects, insertion, deletion, or code execution. The 'search' prefix and sibling tools (cache_query, cache_stats, cache_top_cited) all indicate read-only data retrieval operations.
From the tool's definition Tool name 'search_by_doi' combined with server context: CrossRef is a bibliographic database; searching by DOI (Digital Object Identifier) is a standard lookup/retrieval operation.
Documented attack patterns abuse exactly the kind of access search_by_doi gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Crossref Local, and nothing reaches the server without passing your rules. This is the rule we recommend for search_by_doi:
{
"version": "1",
"default": "deny",
"tools": {
"search_by_doi": {}
}
}search_by_doi 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_doi. It is categorised as a Read tool in the Crossref Local MCP Server, which means it retrieves data without modifying state.
Register the Crossref Local MCP server in PolicyLayer and add a rule for search_by_doi: 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 Crossref Local. Nothing to install.
search_by_doi 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_doi 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_doi. 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_doi is provided by the Crossref Local MCP server (ywatanabe1989/crossref-local). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Crossref Local, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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17 Crossref Local tools catalogued and risk-classified — across an index of 43,000+ MCP servers.