attach_data_to_card
Attach binary data (image, markdown, PDF, text, etc.) to a card from base64-encoded data or a data URL. Use this for any non-image content. For image/screenshot uploads with PNG defaults, see attach_image_data_to_card.
This record as markdown: /tools/io-github-delorenj-mcp-server-trello/attach-data-to-card.md
What attach_data_to_card does on Trello
AI agents use attach_data_to_card to create or update resources in Trello, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Trello environment.
Why attach_data_to_card is rated Medium
This tool modifies card state by adding attachments but does not delete, execute code, or move money. The attachment operation is reversible (attachments can be detached), making it Write rather than Destructive. Severity is medium because malicious attachment of large files or inappropriate content could disrupt workflows, but the blast radius is limited to a single card's attachments.
From the tool's definition Tool description states 'Attach binary data... to a card' and 'uploads', indicating creation/modification of data on Trello cards. This is reversible—attachments can be removed or replaced.
Attacks that exploit this kind of access
The rule that runs attach_data_to_card safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Trello, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For attach_data_to_card, this is the rule to start with:
attach_data_to_card 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.
The button opens the PolicyLayer dashboard: create your workspace, connect Trello, apply this rule, and every attach_data_to_card call is checked against it from then on.
Questions about attach_data_to_card
Attach binary data (image, markdown, PDF, text, etc.) to a card from base64-encoded data or a data URL. Use this for any non-image content. For image/screenshot uploads with PNG defaults, see attach_image_data_to_card. It is categorised as a Write tool in the Trello MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Trello MCP server in PolicyLayer and add a rule for attach_data_to_card: 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. Nothing to install.
attach_data_to_card is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the attach_data_to_card 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.
Set action: deny in the PolicyLayer policy for attach_data_to_card. 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.
attach_data_to_card is provided by the Trello MCP server (@delorenj/mcp-server-trello). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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