add_attachment_url

Add a URL attachment to a Trello card.

SERVERTrello MCP Server SOURCEabdwyer/trellomcp

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/abdwyer-trellomcp/add-attachment-url.md

WHAT IT DOES

What add_attachment_url does on Trello MCP Server

AI agents use add_attachment_url 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.

RISK

Why add_attachment_url is rated Medium

This tool creates new data (an attachment) on a Trello card, which is a reversible write operation. The severity is medium because misuse could clutter cards with unwanted attachments or attach malicious URLs, but the impact is limited to a single card's metadata and can be undone by removing the attachment. It does not execute code, delete data, or move money.

From the tool's definition The tool name 'add_attachment_url' and description 'Add a URL attachment to a Trello card' indicate creation/modification of card data by attaching a URL to an existing card.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs add_attachment_url safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Trello MCP Server, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For add_attachment_url, this is the rule to start with:

add_attachment_url Rate-limited

add_attachment_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": {
    "add_attachment_url": {
      "limits": [
        {
          "counter": "add_attachment_url_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Trello MCP Server, apply this rule, and every add_attachment_url call is checked against it from then on.

FAQ

Questions about add_attachment_url

What does the add_attachment_url tool do? +

Add a URL attachment to a Trello card. 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_url? +

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

What risk level is add_attachment_url? +

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

Can I rate-limit add_attachment_url? +

Yes. Add a rate_limit block to the add_attachment_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 add_attachment_url completely? +

Set action: deny in the PolicyLayer policy for add_attachment_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 add_attachment_url? +

add_attachment_url is provided by the Trello MCP Server MCP server (abdwyer/trellomcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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