Delete a custom field from a subscriber list
AI agents call delete_custom_field to permanently remove resources in Campaign Monitor MCP — typically in cleanup and lifecycle workflows. It does its job in a single call, and there is no undo.
Deleting a custom field is a destructive action that cannot be easily undone. It removes the field definition and potentially associated data across all subscribers in that list. While not as severe as deleting all subscriber records, it irreversibly alters the schema/structure of the subscriber list and could cause downstream issues in dependent processes or integrations.
From the tool's definition Tool name is 'delete_custom_field' with description 'Delete a custom field from a subscriber list'. The verb 'delete' combined with operation on a list's custom field structure indicates irreversible data structure modification.
Attacks that exploit this kind of access
Delete a custom field from a subscriber list. It is categorised as a Destructive tool in the Campaign Monitor MCP MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.
Register the Campaign Monitor MCP server in PolicyLayer and add a rule for delete_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 Campaign Monitor MCP. Nothing to install.
delete_custom_field is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.
Yes. Add a rate_limit block to the delete_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.
Set action: deny in the PolicyLayer policy for delete_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.
delete_custom_field is provided by the Campaign Monitor MCP server (pauliowest/cmon-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
Teams ship this data inside their own products. See what a licence covers →