addAttachmentToCard · Trello MCP Server MCP: Risk & Policy

WHAT IT DOES

What addAttachmentToCard does on Trello MCP Server

AI agents use addAttachmentToCard 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 addAttachmentToCard needs a policy

This tool creates new data (an attachment) on a card, which is a Write operation. It is reversible (attachments can be removed), so it does not qualify as Destructive. The severity is medium because misuse could result in unauthorized modifications to cards (e.g., adding malicious links) but with limited blast radius compared to destructive or financial operations.

From the tool's definition Tool adds/attaches a file or URL to a Trello card, modifying card state. Description: 'Add an attachment to a Trello card. Can attach either a URL or upload a file.' This is a reversible data modification operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

addAttachmentToCard Rate-limited

addAttachmentToCard 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": {
    "addAttachmentToCard": {
      "limits": [
        {
          "counter": "addattachmenttocard_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 addAttachmentToCard

What does the addAttachmentToCard tool do? +

Add an attachment to a Trello card. Can attach either a URL or upload a file. Provide either. 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 addAttachmentToCard? +

Register the Trello MCP Server MCP server in PolicyLayer and add a rule for addAttachmentToCard: 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 addAttachmentToCard? +

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

Can I rate-limit addAttachmentToCard? +

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

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

addAttachmentToCard is provided by the Trello MCP Server MCP server (semblancelabs/trello-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.