apply_patch · MCP Files MCP: Risk & Policy

WHAT IT DOES

What apply_patch does on MCP Files

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

WHY IT NEEDS A POLICY

Why apply_patch needs a policy

apply_patch modifies file content through patch application, making it a Write operation rather than Read. It is not Destructive because patches are reversible and the tool includes validation mechanisms. Severity is medium because an AI agent could misapply patches to introduce bugs, alter critical code, or corrupt files, though the validation and quota enforcement provide some mitigation.

From the tool's definition Tool description states it 'Apply[s]...patches' and 'enforces...writing', indicating it modifies files. The patch application is reversible (patches can be reverted with counter-patches), distinguishing it from destructive operations.

Risk signalsBulk/mass operation — affects multiple targets

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 Files, so you can run agents against it safely.

FAQ

Questions about apply_patch

What does the apply_patch tool do? +

Apply Codex-style or standard unified diff patches. Validates every hunk before writing and enforces quota/extension rules. It is categorised as a Write tool in the MCP Files 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 Files 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 Files. 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 Files MCP server (tspspi/mcpfiles). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.