hg_topic · Mercurial MCP: Risk & Policy

WHAT IT DOES

What hg_topic does on Mercurial

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

WHY IT NEEDS A POLICY

Why hg_topic needs a policy

Creating a new topic in Mercurial is a reversible write operation that sets up a named topic for organizing changesets. It does not delete data, execute arbitrary code, or involve financial transactions. Severity is low as topics are lightweight metadata and easy to undo.

From the tool's definition Creates a new topic

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

hg_topic Rate-limited

hg_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": {
    "hg_topic": {
      "limits": [
        {
          "counter": "hg_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 Mercurial, so you can run agents against it safely.

FAQ

Questions about hg_topic

What does the hg_topic tool do? +

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

How do I enforce a policy on hg_topic? +

Register the Mercurial MCP server in PolicyLayer and add a rule for hg_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 Mercurial. Nothing to install.

What risk level is hg_topic? +

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

Can I rate-limit hg_topic? +

Yes. Add a rate_limit block to the hg_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 hg_topic completely? +

Set action: deny in the PolicyLayer policy for hg_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 hg_topic? +

hg_topic is provided by the Mercurial MCP server (metal-shark-sharktech/mcp-server-mercurial). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.