script_apply_diff

THE RISK

Medium Risk

Why script_apply_diff needs a policy

Applying diffs rewrites script content reversibly, making this a Write operation rather than Destructive (diffs can be reversed). Severity is high because modifying C# scripts in a Unity project could introduce bugs, break builds, or compromise game logic, though the effect is reversible. Confidence is high given the explicit diff-application semantics.

From the tool's definition Tool applies diffs to C# scripts—modifying existing code in place. Description states 'Apply a unified diff to a C# script', which is a code modification operation.

Documented attack patterns abuse exactly the kind of access script_apply_diff gives an agent:

POLICY

How to control script_apply_diff

PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Server for Unity, and nothing reaches the server without passing your rules. This is the rule we recommend for script_apply_diff:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "script_apply_diff": {
      "limits": [
        {
          "counter": "script_apply_diff_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

script_apply_diff 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.

Create a free account and register MCP Server for Unity — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More MCP Server for Unity tools

Destructive folder_delete Delete a folder from Unity project Destructive script_delete Delete a C script from Unity project Destructive shader_delete Delete a shader from Unity project Write folder_create Create a new folder in Unity project Write folder_move Move a folder to a new location in Unity project Write folder_rename Rename a folder in Unity project Write script_create Create a new C script in Unity project Write setup_unity_bridge Install/update Unity MCP bridge scripts to a Unity project (works even if Unity server is

All 15 MCP Server for Unity tools →

Write tools on other servers

M-Team MCP Server download_torrent YouTube MCP Server generate_video_title Android Forensics ADB MCP Server combine_reports 0xarchive web3_signup

Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about script_apply_diff

What does the script_apply_diff tool do? +

Apply a unified diff to a C# script. It is categorised as a Write tool in the MCP Server for Unity MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on script_apply_diff? +

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

What risk level is script_apply_diff? +

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

Can I rate-limit script_apply_diff? +

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

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

script_apply_diff is provided by the MCP Server for Unity MCP server (zabaglione/mcp-server-unity). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every MCP Server for Unity tool call.

Start from MCP Server for Unity, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →