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damientilman

Mailchimp MCP

list_merge_fields

Retrieve merge fields (custom data fields) for a Mailchimp audience to discover available tags and field types before adding or updating members.

Instructions

List merge fields (custom data fields) defined for an audience, including tags, types, and defaults.

Use to discover available merge fields and their tag names before adding or updating members. Default fields (FNAME, LNAME, ADDRESS, PHONE) are always present. Use create_merge_field to add custom fields. Merge field tags are used in add_member/update_member merge_fields objects and in email content as |TAG| merge tags.

Authenticated via API key. Subject to Mailchimp API rate limits (max 10 concurrent requests). Read-only, safe to retry.

Args: list_id: The Mailchimp audience/list ID (e.g. 'abc123def4'). Obtain from list_audiences. count: Number of merge fields to return (1-1000, default 50). offset: Pagination offset. Use when total_items exceeds count.

Returns: JSON with total_items and merge_fields array. Each field: merge_id (int, use with update_merge_field/delete_merge_field), tag (string, e.g. 'FNAME'), name (display name), type ('text', 'number', 'date', etc.), required (boolean), default_value, options (choices for dropdown/radio types).

Example: list_merge_fields(list_id="abc123") -> {"total_items": 6, "merge_fields": [{"merge_id": 1, "tag": "FNAME", "name": "First Name", "type": "text", ...}]}

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
list_idYes
countNo
offsetNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior5/5

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

With no annotations, the description carries full burden. It discloses that the tool is read-only, safe to retry, requires API key authentication, and is subject to rate limits. It also explains the return format, adding significant behavioral context.

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 well-structured with sections (purpose, usage, defaults, args, returns, example) and is front-loaded. It is detailed but each sentence adds value; slightly verbose but still concise given the information needed.

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

Completeness5/5

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

Given zero annotations and 0% schema descriptions, the description is fully complete: it covers all parameters, return structure, example, authentication, rate limits, read-only nature, and relationship to other tools. Output schema exists, but the return explanation adds clarity.

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

Parameters5/5

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

Schema description coverage is 0%, so description fully compensates. It explains list_id (obtain from list_audiences), count (range 1-1000, default 50), offset (pagination when total_items exceeds count), adding meaning beyond schema types.

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 explicitly states 'list merge fields (custom data fields) defined for an audience', providing a clear verb and resource. It distinguishes from siblings by noting that default fields are always present and that create_merge_field is used for custom fields, and relates to add_member/update_member.

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

Usage Guidelines4/5

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

It advises 'Use to discover available merge fields and their tag names before adding or updating members', and mentions alternatives like create_merge_field. It does not explicitly state when not to use, but gives strong contextual guidance.

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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