hg_rebase · Mercurial MCP: Risk & Policy

WHAT IT DOES

What hg_rebase does on Mercurial

AI agents invoke hg_rebase 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_rebase needs a policy

Rebase rewrites commit history (non-trivially reversible but potentially destructive if done wrong), replays changesets onto a new destination, and can alter the repository's DAG structure. It is not a simple write but an execution of a complex operation. While technically reversible with evolve/undo in Mercurial, it can cause data loss or conflicts if misused, placing it at Execute with high severity.

From the tool's definition 'Rebases changes onto a destination' — rebase rewrites commit history by replaying changesets onto a new base, which is a complex repository operation with significant side effects

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

hg_rebase Rate-limited

hg_rebase 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_rebase": {
      "limits": [
        {
          "counter": "hg_rebase_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_rebase

What does the hg_rebase tool do? +

Rebases changes onto a destination. 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_rebase? +

Register the Mercurial MCP server in PolicyLayer and add a rule for hg_rebase: 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_rebase? +

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

Can I rate-limit hg_rebase? +

Yes. Add a rate_limit block to the hg_rebase 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_rebase completely? +

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

hg_rebase 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.