Mailchimp MCP Server

create_merge_field

Create a custom merge field for a Mailchimp audience list, supporting types like text, number, date, dropdown, and more.

Instructions

Create a custom merge field. field_type: text, number, address, phone, date, url, dropdown, radio, birthday.

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>",
      "name": "<name>"
    },
    "name": "create_merge_field"
  }
}

Input Schema

Name	Required	Default
`list_id`	Yes
`name`	Yes
`field_type`	No	text
`tag`	No
`required`	No
`default_value`	No

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Addedv0.2.0May 2, 2026

TDQS

C2.9/5.0

Behavior2/5

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

With no annotations provided, the description bears full responsibility for behavioral disclosure. It only states the creation intent and field types, but lacks details on permissions, side effects (e.g., if field already exists), or response outcomes. This is insufficient for safe invocation.

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 concise: a single sentence plus a list. It front-loads the action and enumerates types efficiently. However, it could be slightly more structured to improve readability without increasing length.

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

Completeness2/5

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

Given 6 parameters, 0% schema coverage, and no annotations, the description is far from complete. It does not explain what list_id refers to, naming rules, the meaning of tag, or how required and default_value interact. The existence of an output schema is not leveraged. The agent would need to guess critical details.

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

Parameters2/5

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

Schema description coverage is 0%, so the description must compensate. It only explains field_type values, leaving five other parameters (list_id, name, tag, required, default_value) undocumented in meaning or constraints. This fails to add meaning beyond the schema's minimal type info.

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?

The description clearly states the action 'create' and the resource 'custom merge field', and lists the allowed field_type values, making the tool's purpose specific and distinguishable from siblings like list_merge_fields.

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?

The description provides no guidance on when to use this tool, prerequisites, or alternatives. It does not mention required parameters like list_id or context for field creation, leaving the agent without usage context.

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

Deploy Server