Campaign Monitor MCP

create_custom_field

Add a new custom field to a subscriber list by specifying name, data type, and visibility in the preference center.

Instructions

Create a new custom field for a subscriber list

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "list_id": "<list_id>",
      "field_name": "<field_name>",
      "data_type": "<data_type>"
    },
    "name": "create_custom_field"
  }
}

Input Schema

Name	Required	Description
`list_id`	Yes	The list ID
`field_name`	Yes	Name of the custom field
`data_type`	Yes	Data type: 'Text', 'Number', 'MultiSelectOne', 'MultiSelectMany', 'Date', or 'Country'
`visible_in_preference_center`	No	Whether the field is visible in the subscriber preference center

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0May 20, 2026

TDQS

B3.2/5.0

Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations provided, so the description carries full burden. It only states 'create' but does not disclose side effects, permissions needed, naming constraints, or what happens on duplicate field names. This is insufficient for a mutation tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single sentence with no wasted words. It is front-loaded but could benefit from slightly more detail without becoming verbose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool has 4 parameters (3 required) and no output schema, the description is adequate for a simple create operation but lacks information about return values (e.g., created field ID). It is minimally complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

All four parameters are fully described in the input schema (100% coverage). The description adds no additional meaning beyond the schema. Baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description clearly states the tool creates a custom field for a subscriber list. It uses a specific verb ('Create') and resource ('custom field'), distinguishing it from sibling tools like update_custom_field and delete_custom_field.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance on when to use this tool versus alternatives, such as updating or deleting. No prerequisites or conditions mentioned. The agent is left to infer context from the tool name alone.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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