mcp_replace_in_file · Local Code MCP: Risk & Policy

WHAT IT DOES

What mcp_replace_in_file does on Local Code

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

WHY IT NEEDS A POLICY

Why mcp_replace_in_file needs a policy

The tool creates or modifies data (file contents) reversibly through text replacement. While it can change code, it is not destructive (changes can be undone via version control or file recovery) and does not delete data. It aligns with the Write category. Severity is medium because misuse could introduce bugs or security issues into code, but the local scope and reversibility limit the blast radius.

From the tool's definition Tool description states 'Replace exact text snippets in a file' with parameters for old/new text replacements. This modifies file content reversibly.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

mcp_replace_in_file Rate-limited

mcp_replace_in_file 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": {
    "mcp_replace_in_file": {
      "limits": [
        {
          "counter": "mcp_replace_in_file_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 Local Code, so you can run agents against it safely.

FAQ

Questions about mcp_replace_in_file

What does the mcp_replace_in_file tool do? +

Replace exact text snippets in a file. replacements_json is a JSON list with old/new/replace_all. It is categorised as a Write tool in the Local Code MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on mcp_replace_in_file? +

Register the Local Code MCP server in PolicyLayer and add a rule for mcp_replace_in_file: 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 Local Code. Nothing to install.

What risk level is mcp_replace_in_file? +

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

Can I rate-limit mcp_replace_in_file? +

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

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

mcp_replace_in_file is provided by the Local Code MCP server (js190-prog/local-code-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.