pubsub.create-topic · MCP: Risk & Policy

WHAT IT DOES

What pubsub.create-topic does on Mcp

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

WHY IT NEEDS A POLICY

Why pubsub.create-topic needs a policy

The tool creates a new resource (a pubsub topic) owned by the user's wallet. This is a Write operation because it creates data reversibly—topics can typically be deleted or modified. Severity is medium because scope is limited to the caller's wallet (no cross-user blast radius), but misconfiguration could lead to unintended topic proliferation or disruption of messaging patterns.

From the tool's definition Tool description states 'create a topic', which is a reversible creation operation that modifies state within the caller's wallet scope.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

pubsub.create-topic Rate-limited

pubsub.create-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": {
    "pubsub.create-topic": {
      "limits": [
        {
          "counter": "pubsub.create-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 Mcp, so you can run agents against it safely.

FAQ

Questions about pubsub.create-topic

What does the pubsub.create-topic tool do? +

PUBSUB: create a topic you own, scoped to YOUR wallet. It is categorised as a Write tool in the 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 pubsub.create-topic? +

Register the MCP server in PolicyLayer and add a rule for pubsub.create-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 Mcp. Nothing to install.

What risk level is pubsub.create-topic? +

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

Can I rate-limit pubsub.create-topic? +

Yes. Add a rate_limit block to the pubsub.create-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 pubsub.create-topic completely? +

Set action: deny in the PolicyLayer policy for pubsub.create-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 pubsub.create-topic? +

pubsub.create-topic is provided by the MCP server (@2sio/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.