generate_file_upload_url · Opus MCP Server MCP

WHAT IT DOES

What generate_file_upload_url does on Opus MCP Server

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

WHY IT NEEDS A POLICY

Why generate_file_upload_url needs a policy

This tool creates new file entries and enables file uploads, which is a reversible write operation. While it doesn't directly modify existing data, it adds new files to the system that can subsequently be used in job execution workflows.

From the tool's definition Generates a presigned URL for file upload, enabling creation of new file objects in the Opus system. The tool explicitly returns a presignedUrl for uploading and fileUrl for referencing, indicating it facilitates the addition of new data to the platform.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

generate_file_upload_url Rate-limited

generate_file_upload_url 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": {
    "generate_file_upload_url": {
      "limits": [
        {
          "counter": "generate_file_upload_url_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Opus MCP Server, so you can run agents against it safely.

FAQ

Questions about generate_file_upload_url

What does the generate_file_upload_url tool do? +

Generate presigned URL for file upload. Returns presignedUrl (for uploading) and fileUrl (to reference in job execution). It is categorised as a Write tool in the Opus MCP 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 generate_file_upload_url? +

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

What risk level is generate_file_upload_url? +

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

Can I rate-limit generate_file_upload_url? +

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

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

generate_file_upload_url is provided by the Opus MCP Server MCP server (moenamatics/opus-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.