get_unique_values

THE RISK

Low Risk

Why get_unique_values needs a policy

This tool retrieves metadata information from an Obsidian vault without creating, modifying, deleting, or executing any operations. It is a passive read operation that extracts and lists existing data. The blast radius of misuse is minimal—an agent could only enumerate metadata values, not alter or destroy data.

From the tool's definition Tool name 'get_unique_values' and description 'Get all unique values for a metadata field' indicate a query/retrieval operation with no modification or side effects.

Documented attack patterns abuse exactly the kind of access get_unique_values gives an agent:

POLICY

How to control get_unique_values

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 get_unique_values:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "get_unique_values": {}
  }
}

get_unique_values is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Obsidian MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about get_unique_values

What does the get_unique_values tool do? +

Get all unique values for a metadata field. It is categorised as a Read tool in the Obsidian MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on get_unique_values? +

Register the Obsidian MCP Server MCP server in PolicyLayer and add a rule for get_unique_values: 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.

What risk level is get_unique_values? +

get_unique_values is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit get_unique_values? +

Yes. Add a rate_limit block to the get_unique_values 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.

How do I block get_unique_values completely? +

Set action: deny in the PolicyLayer policy for get_unique_values. 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.

What MCP server provides get_unique_values? +

get_unique_values is provided by the Obsidian MCP Server MCP server (bazylhorsey/obsidian-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Obsidian MCP Server tool call.

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.

CHECK YOUR STACK →