publish_topic · Joulescope MCP: Risk & Policy

WHAT IT DOES

What publish_topic does on Joulescope

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

WHY IT NEEDS A POLICY

Why publish_topic needs a policy

Publishing to a topic on an instrument control server like JouleScope typically creates or modifies configuration or state data. This is a reversible Write operation rather than a Read (no retrieval), Execute (no code/script execution), Destructive (not irreversible), or Financial action.

From the tool's definition Tool name 'publish_topic' indicates writing/publishing data to a topic, which modifies state on the JouleScope device or its connected systems. The description is empty, limiting certainty.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

publish_topic Rate-limited

publish_topic 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": {
    "publish_topic": {
      "limits": [
        {
          "counter": "publish_topic_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 Joulescope, so you can run agents against it safely.

FAQ

Questions about publish_topic

What does the publish_topic tool do? +

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

How do I enforce a policy on publish_topic? +

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

What risk level is publish_topic? +

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

Can I rate-limit publish_topic? +

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

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

publish_topic is provided by the Joulescope MCP server (juanqui/joulescope-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.