hg_evolve · Mercurial MCP: Risk & Policy

WHAT IT DOES

What hg_evolve does on Mercurial

AI agents invoke hg_evolve to trigger actions in Mercurial. 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 hg_evolve needs a policy

hg evolve is a Mercurial command that automatically resolves unstable changesets by rewriting history (rebasing, updating, or obsoleting changesets). This constitutes a complex execution that modifies repository state in potentially far-reaching ways.

From the tool's definition 'Evolves the repository to resolve instabilities' — triggers the Mercurial evolve operation which rewrites and reorganizes changesets, altering repository history

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

hg_evolve Rate-limited

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

FAQ

Questions about hg_evolve

What does the hg_evolve tool do? +

Evolves the repository to resolve instabilities. It is categorised as a Execute tool in the Mercurial MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on hg_evolve? +

Register the Mercurial MCP server in PolicyLayer and add a rule for hg_evolve: 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_evolve? +

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

Can I rate-limit hg_evolve? +

Yes. Add a rate_limit block to the hg_evolve 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_evolve completely? +

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

hg_evolve 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.