batch_array_unique · Frontmatter MCP: Risk & Policy

WHAT IT DOES

What batch_array_unique does on Frontmatter MCP

AI agents use batch_array_unique to create or update resources in Frontmatter MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Frontmatter MCP environment.

WHY IT NEEDS A POLICY

Why batch_array_unique needs a policy

The tool operates on frontmatter metadata arrays, likely deduplicating values within an array field across multiple documents. This is a reversible modification (arrays can be restored), making it Write rather than Destructive. The empty description lowers confidence slightly, but the pattern from sibling batch-operation tools and context of frontmatter mutation makes Write the appropriate category.

From the tool's definition Tool name 'batch_array_unique' paired with sibling tools 'batch_array_add', 'batch_array_remove', 'batch_array_replace', and 'batch_update'. These are clearly data modification operations on array fields within frontmatter metadata.

Risk signalsBulk/mass operation — affects multiple targets

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

batch_array_unique Rate-limited

batch_array_unique stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "batch_array_unique": {
      "limits": [
        {
          "counter": "batch_array_unique_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Frontmatter MCP, so you can run agents against it safely.

FAQ

Questions about batch_array_unique

What does the batch_array_unique tool do? +

batch_array_unique. It is categorised as a Write tool in the Frontmatter MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on batch_array_unique? +

Register the Frontmatter MCP server in PolicyLayer and add a rule for batch_array_unique: 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 Frontmatter MCP. Nothing to install.

What risk level is batch_array_unique? +

batch_array_unique is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit batch_array_unique? +

Yes. Add a rate_limit block to the batch_array_unique 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 batch_array_unique completely? +

Set action: deny in the PolicyLayer policy for batch_array_unique. 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 batch_array_unique? +

batch_array_unique is provided by the Frontmatter MCP server (kzmshx/frontmatter-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.