rebase · Jj MCP: Risk & Policy

WHAT IT DOES

What rebase does on Jj

AI agents invoke rebase to trigger actions in Jj. 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 rebase needs a policy

Rebase restructures commit history by replaying commits onto a new parent, which is a potentially complex operation that rewrites commit history. While it can be partially undone in version control, it can cause conflicts, alter commit hashes, and disrupt collaborators' work.

From the tool's definition Rebase one or more revisions onto a different parent revision... move changes to a new base or to clean up commit history

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

rebase Rate-limited

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": {
    "rebase": {
      "limits": [
        {
          "counter": "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 Jj, so you can run agents against it safely.

FAQ

Questions about rebase

What does the rebase tool do? +

Rebase one or more revisions onto a different parent revision in a Jujutsu (jj) repository. Commonly used to move changes to a new base or to clean up commit history. Parameters: source (Revisions to rebase, e.g.,. It is categorised as a Execute tool in the Jj MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on rebase? +

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

What risk level is rebase? +

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

Can I rate-limit rebase? +

Yes. Add a rate_limit block to the 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 rebase completely? +

Set action: deny in the PolicyLayer policy for 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 rebase? +

rebase is provided by the Jj MCP server (jj-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.