grep_replace · Melo MCP: Risk & Policy

WHAT IT DOES

What grep_replace does on Melo

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

WHY IT NEEDS A POLICY

Why grep_replace needs a policy

This tool creates or modifies data (script content) reversibly through a staged diff workflow, making it a Write operation. Severity is high because a single invocation can affect numerous scripts at once with regex support, creating broad blast radius if an agent crafts an unintended pattern. The dryRun option and staged review process mitigate some risk but do not prevent the Write action itself.

From the tool's definition "Find and replace text across all scripts. Changes are staged as diffs for review." The tool modifies script content across multiple files simultaneously.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

grep_replace Rate-limited

grep_replace 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": {
    "grep_replace": {
      "limits": [
        {
          "counter": "grep_replace_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 Melo, so you can run agents against it safely.

FAQ

Questions about grep_replace

What does the grep_replace tool do? +

Find and replace text across all scripts. Changes are staged as diffs for review. Args: - find (string): Text or pattern to find - replace (string): Replacement text - useRegex (boolean, optional): Use regex matching (default: false) - scriptType (string, optional): Filter by script type - dryRun (boolean, optional): Preview changes without staging (default: false) Returns: Summary of all scripts affected with diff previews. It is categorised as a Write tool in the Melo MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on grep_replace? +

Register the Melo MCP server in PolicyLayer and add a rule for grep_replace: 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 Melo. Nothing to install.

What risk level is grep_replace? +

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

Can I rate-limit grep_replace? +

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

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

grep_replace is provided by the Melo MCP server (yannyhl/linkedsword-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.