publish_message · Gcp MCP: Risk & Policy

WHAT IT DOES

What publish_message does on Gcp

AI agents invoke publish_message to trigger actions in Gcp. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why publish_message needs a policy

Publishing a message to a Pub/Sub topic triggers external operations and downstream consumers. The effects depend entirely on the message content and topic subscribers — it can initiate workflows, data pipelines, or system actions. This is classified as Execute because it triggers external operations whose effects depend on arguments, not merely writing data to a store.

From the tool's definition Publish a message to a Pub/Sub topic

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

publish_message Rate-limited

publish_message stays usable, but rate-capped — a runaway agent can't fire it dozens of times 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_message": {
      "limits": [
        {
          "counter": "publish_message_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about publish_message

What does the publish_message tool do? +

Publish a message to a Pub/Sub topic. It is categorised as a Execute tool in the Gcp MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on publish_message? +

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

What risk level is publish_message? +

publish_message is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit publish_message? +

Yes. Add a rate_limit block to the publish_message 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_message completely? +

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

publish_message is provided by the Gcp MCP server (lokimcpuniverse/gcp-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.