update_card_custom_field

Set or clear a custom field value on a card. Requires Trello Standard plan or higher.

SERVERTrello SOURCE@delorenj/mcp-server-trello

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/io-github-delorenj-mcp-server-trello/update-card-custom-field.md

WHAT IT DOES

What update_card_custom_field does on Trello

AI agents use update_card_custom_field 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.

RISK

Why update_card_custom_field is rated Medium

This tool modifies card metadata (custom field values) but does not delete cards, execute arbitrary code, move money, or cause irreversible damage. The operation is reversible—a custom field can be updated or cleared again. Severity is medium because misuse could corrupt card data or alter project tracking information on shared Trello boards, but the impact is limited to a single field and easily corrected.

From the tool's definition Tool description states 'Set or clear a custom field value on a card', indicating modification of card data. The verb 'Set' and 'clear' are reversible write operations.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs update_card_custom_field 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 update_card_custom_field, this is the rule to start with:

update_card_custom_field Rate-limited

update_card_custom_field 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": {
    "update_card_custom_field": {
      "limits": [
        {
          "counter": "update_card_custom_field_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, apply this rule, and every update_card_custom_field call is checked against it from then on.

FAQ

Questions about update_card_custom_field

What does the update_card_custom_field tool do? +

Set or clear a custom field value on a card. Requires Trello Standard plan or higher. 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.

How do I enforce a policy on update_card_custom_field? +

Register the Trello MCP server in PolicyLayer and add a rule for update_card_custom_field: 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.

What risk level is update_card_custom_field? +

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

Can I rate-limit update_card_custom_field? +

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

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

update_card_custom_field 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.

KEEP EXPLORING

More on Trello, and thousands of servers like it.

This server

All 50 Trello tools →

Across the catalogue

aroflo_create_or_update_record on AroFlo MCP →team_manager_update_budget on Team Manager MCP → The MCP Attack Database →

Guides

Govern customer-ops agents →Argument validation →Scoped token →