add_attachment · Trello MCP Server MCP: Risk & Policy

WHAT IT DOES

What add_attachment does on Trello MCP Server

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

WHY IT NEEDS A POLICY

Why add_attachment needs a policy

An AI agent can call add_attachment faster than any human can review — one bad instruction and it creates or modifies resources in Trello MCP Server by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_attachment Rate-limited

add_attachment 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": {
    "add_attachment": {
      "limits": [
        {
          "counter": "add_attachment_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 Trello MCP Server, so you can run agents against it safely.

FAQ

Questions about add_attachment

What does the add_attachment tool do? +

Add a URL attachment to a card. Only URLs are supported (no file uploads). It is categorised as a Write tool in the Trello 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 add_attachment? +

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

What risk level is add_attachment? +

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

Can I rate-limit add_attachment? +

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

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

add_attachment is provided by the Trello MCP Server MCP server (pypi:fastmcp-trello). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.