set_themes · Pen MCP: Risk & Policy

WHAT IT DOES

What set_themes does on Pen

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

WHY IT NEEDS A POLICY

Why set_themes needs a policy

The tool creates or updates theme configurations in an OpenPencil document file. These are write operations that modify data but are reversible (themes can be updated again or deleted). The blast radius is moderate—incorrect theme application could affect document appearance across multiple pages, but the changes are not destructive (data is not deleted) and can be corrected.

From the tool's definition Tool description states 'Create or update theme axes and their variants in an .op file', which are reversible write operations that modify document data structures.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_themes Rate-limited

set_themes 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": {
    "set_themes": {
      "limits": [
        {
          "counter": "set_themes_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 Pen, so you can run agents against it safely.

FAQ

Questions about set_themes

What does the set_themes tool do? +

Create or update theme axes and their variants in an .op file. Each theme axis (e.g. It is categorised as a Write tool in the Pen MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_themes? +

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

What risk level is set_themes? +

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

Can I rate-limit set_themes? +

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

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

set_themes is provided by the Pen MCP server (@zseven-w/pen-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.