# update_card_custom_field

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

Agent View of the PolicyLayer registry record for `update_card_custom_field`. HTML page: https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/update-card-custom-field

## Facts

- Tool: `update_card_custom_field`
- Server: Trello (`@delorenj/mcp-server-trello`) — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello.md
- Install: `npx -y @delorenj/mcp-server-trello`
- Homepage: https://github.com/delorenj/mcp-server-trello
- Risk category: Write (Medium risk)
- Registry record: grade F, identity unverified
- Server rate-limited: no
- Parameters: 0
- Recommended policy verdict: Rate-limited

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "update_card_custom_field",
    "arguments": {}
  }
}
```

## 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 own 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."

## Use case

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.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Trello:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "update_card_custom_field": {
      "limits": [
        {
          "counter": "update_card_custom_field_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on Trello (49)

- `archive_list` — Destructive — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/archive-list.md
- `delete_checklist_item` — Destructive — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/delete-checklist-item.md
- `delete_comment` — Destructive — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/delete-comment.md
- `delete_label` — Destructive — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/delete-label.md
- `download_attachment` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/download-attachment.md
- `find_checklist_items_by_description` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/find-checklist-items-by-description.md
- `get_acceptance_criteria` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-acceptance-criteria.md
- `get_active_board_info` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-active-board-info.md
- `get_board_custom_fields` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-board-custom-fields.md
- `get_board_labels` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-board-labels.md
- `get_board_members` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-board-members.md
- `get_card` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-card.md
- `get_card_comments` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-card-comments.md
- `get_card_history` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-card-history.md
- `get_cards_by_list_id` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-cards-by-list-id.md
- `get_checklist_by_name` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-checklist-by-name.md
- `get_checklist_items` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-checklist-items.md
- `get_lists` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-lists.md
- `get_my_cards` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-my-cards.md
- `get_recent_activity` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/get-recent-activity.md
- `list_boards` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/list-boards.md
- `list_boards_in_workspace` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/list-boards-in-workspace.md
- `list_workspaces` — Read — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/list-workspaces.md
- `add_card_to_list` — Write — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/add-card-to-list.md
- `add_cards_to_list` — Write — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/add-cards-to-list.md
- `add_checklist_item` — Write — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/add-checklist-item.md
- `add_comment` — Write — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/add-comment.md
- `add_list_to_board` — Write — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/add-list-to-board.md
- `archive_card` — Write — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/archive-card.md
- `assign_member_to_card` — Write — https://policylayer.com/tools/io-github-delorenj-mcp-server-trello/assign-member-to-card.md
- …and 19 more: https://policylayer.com/tools/io-github-delorenj-mcp-server-trello.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=io-github-delorenj-mcp-server-trello · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/io-github-delorenj-mcp-server-trello