replace_js_imports · Filesystem MCP: Risk & Policy

WHAT IT DOES

What replace_js_imports does on FilesystemMCP

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

WHY IT NEEDS A POLICY

Why replace_js_imports needs a policy

This tool creates or modifies file content (the imports section) reversibly. While modification of imports could have downstream effects on code behavior, the operation itself is Write—the modified imports can be reverted by providing different content. It does not delete files or irreversibly destroy data (Destructive), execute arbitrary code (Execute), or move money (Financial).

From the tool's definition Tool performs 'replace the entire imports block' of a JavaScript file, which modifies file content. Description explicitly states it 'replace[s]' and 'newContent should contain only the new import statements', indicating modification rather than deletion.

Risk signalsBulk/mass operation — affects multiple targets

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

replace_js_imports Rate-limited

replace_js_imports 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": {
    "replace_js_imports": {
      "limits": [
        {
          "counter": "replace_js_imports_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 FilesystemMCP, so you can run agents against it safely.

FAQ

Questions about replace_js_imports

What does the replace_js_imports tool do? +

Replace the entire imports block of a JavaScript file. Use get_js_imports first to see the current imports. newContent should contain only the new import statements. Only works within allowed directories. It is categorised as a Write tool in the FilesystemMCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on replace_js_imports? +

Register the Filesystem MCP server in PolicyLayer and add a rule for replace_js_imports: 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 FilesystemMCP. Nothing to install.

What risk level is replace_js_imports? +

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

Can I rate-limit replace_js_imports? +

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

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

replace_js_imports is provided by the Filesystem MCP server (rijadalisic/filesystemmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.