AI agents call search_regex to retrieve information from Obsidian MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves data from notes matching regex patterns without creating, modifying, deleting, or executing operations. It is a standard search/query function with minimal risk when misused—the worst outcome would be discovering unintended information the user already has access to within their own vault.
From the tool's definition Tool name 'search_regex' combined with description 'Search notes using regular expressions' indicates querying/retrieval functionality with no side effects. The verb 'search' and lack of any modification language confirm this is a read-only operation.
Documented attack patterns abuse exactly the kind of access search_regex gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Obsidian MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for search_regex:
{
"version": "1",
"default": "deny",
"tools": {
"search_regex": {}
}
}search_regex is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Search notes using regular expressions. It is categorised as a Read tool in the Obsidian MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Obsidian MCP Server MCP server in PolicyLayer and add a rule for search_regex: 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 Obsidian MCP Server. Nothing to install.
search_regex 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_regex 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_regex. 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_regex is provided by the Obsidian MCP Server MCP server (kynlos/obsidian-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Obsidian MCP 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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120 Obsidian MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.