upload_object · Storage MCP: Risk & Policy

WHAT IT DOES

What upload_object does on Storage

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

WHY IT NEEDS A POLICY

Why upload_object needs a policy

This tool creates new data objects in GCS buckets. While reversible (files can be deleted), it modifies the storage state. It's categorized as Write rather than Execute because the primary action is data creation, not command execution.

From the tool's definition Tool uploads a file to a GCS bucket, which creates/adds data to cloud storage. The description explicitly states 'Uploads a file', confirming data creation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

upload_object Rate-limited

upload_object 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": {
    "upload_object": {
      "limits": [
        {
          "counter": "upload_object_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 Storage, so you can run agents against it safely.

FAQ

Questions about upload_object

What does the upload_object tool do? +

Uploads a file to a GCS bucket. It is categorised as a Write tool in the Storage MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on upload_object? +

Register the Storage MCP server in PolicyLayer and add a rule for upload_object: 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 Storage. Nothing to install.

What risk level is upload_object? +

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

Can I rate-limit upload_object? +

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

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

upload_object is provided by the Storage MCP server (@google-cloud/storage-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.