create_signed_upload · Posterly MCP: Risk & Policy

WHAT IT DOES

What create_signed_upload does on Posterly

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

WHY IT NEEDS A POLICY

Why create_signed_upload needs a policy

This tool enables creation of new media assets (images/videos) by uploading binary content to cloud storage. This is a reversible write operation — the uploaded files can be deleted or modified later. It does not execute arbitrary code, delete data irreversibly, or move money, placing it in the Write category.

From the tool's definition The tool description states 'Create a signed upload URL for a larger image or video. Upload the binary to upload_url; the API validates actual bytes before storage, then public_url can be used with create_post.' This explicitly involves uploading and storing…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_signed_upload Rate-limited

create_signed_upload 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": {
    "create_signed_upload": {
      "limits": [
        {
          "counter": "create_signed_upload_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 Posterly, so you can run agents against it safely.

FAQ

Questions about create_signed_upload

What does the create_signed_upload tool do? +

Create a signed upload URL for a larger image or video. Upload the binary to upload_url; the API validates actual bytes before storage, then public_url can be used with create_post. It is categorised as a Write tool in the Posterly MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on create_signed_upload? +

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

What risk level is create_signed_upload? +

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

Can I rate-limit create_signed_upload? +

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

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

create_signed_upload is provided by the Posterly MCP server (posterly-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.