revert · Jj MCP: Risk & Policy

WHAT IT DOES

What revert does on Jj

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

WHY IT NEEDS A POLICY

Why revert needs a policy

Revert creates new commits that reverse prior changes — it does not delete history. This is a reversible write operation (the revert itself can be reverted), making it Write rather than Destructive. Misuse could introduce incorrect changes to the repository, but the original history is preserved.

From the tool's definition Creates new changes that undo the specified commits. Useful for safely undoing changes.

Risk signalsAdmin/system-level operation

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

revert Rate-limited

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

FAQ

Questions about revert

What does the revert tool do? +

Apply the reverse of one or more revisions in a Jujutsu (jj) repository. Creates new changes that undo the specified commits. Useful for safely undoing changes. Parameters: revisions (Revisions to revert), destination (Optional destination revision, where to apply the revert), repoPath (Optional path to repo root or working directory), cwd (Optional working directory to run the command in). It is categorised as a Write tool in the Jj MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on revert? +

Register the Jj MCP server in PolicyLayer and add a rule for revert: 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 revert? +

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

Can I rate-limit revert? +

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

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

revert 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.