apply_patch · MCP Workspace Server MCP: Risk & Policy

WHAT IT DOES

What apply_patch does on MCP Workspace Server

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

WHY IT NEEDS A POLICY

Why apply_patch needs a policy

This is a Write operation because it modifies and updates file content reversibly. It's not Destructive because patches preserve most of the file and can be reverted; not Execute because it doesn't run code or commands (it modifies text); not Read because it has side effects.

From the tool's definition Tool applies patches to existing files, modifying their content. The patch format (<<<OLD...===...>>>NEW) indicates it replaces specific sections within files rather than creating new ones or deleting them entirely.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

apply_patch Rate-limited

apply_patch 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": {
    "apply_patch": {
      "limits": [
        {
          "counter": "apply_patch_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 MCP Workspace Server, so you can run agents against it safely.

FAQ

Questions about apply_patch

What does the apply_patch tool do? +

Apply a patch to an existing file in the workspace. Uses a simple patch format: <<<OLD\\n...\\n===\\n...\\n>>>NEW. It is categorised as a Write tool in the MCP Workspace Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on apply_patch? +

Register the MCP Workspace Server MCP server in PolicyLayer and add a rule for apply_patch: 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 MCP Workspace Server. Nothing to install.

What risk level is apply_patch? +

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

Can I rate-limit apply_patch? +

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

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

apply_patch is provided by the MCP Workspace Server MCP server (shayyeffet/ultimate_mcp_server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.