Add contacts to an email list by providing one email address or up to 1000 contacts in bulk, with optional metadata for each contact.
Add contacts to a list: one via email, or up to 1000 via contacts.
| Name | Required | Description | Default |
|---|---|---|---|
| No | Single contact email address | ||
| list_id | Yes | Contact list UUID | |
| contacts | No | Bulk contacts (up to 1000) | |
| metadata | No | Metadata for the single contact |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden. It discloses the 1000-contact bulk limit and the two modes, but omits important mutation behavior such as duplicate handling, validation rules, permissions, error behavior, and what the call returns.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single front-loaded sentence with no wasted words. It efficiently conveys the core action and the two usage modes.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a mutation tool with no annotations, no output schema, and nested objects, the description covers the essential input modes and limit. It still leaves out operational details that would help an agent invoke it safely, such as duplicate behavior, required list state, and response semantics.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so the schema already explains the email, contacts, list_id, and metadata fields. The description reinforces the single-vs-bulk distinction but does not clarify mutual exclusivity between email and contacts or how top-level metadata relates to bulk contact metadata.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb and resource: adding contacts to a list. It also distinguishes the two supported modes (single email vs. bulk contacts), which sets it apart from contact-list management siblings like create_contact_list or remove_contact.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
It gives explicit guidance on mode selection: one contact via email, or up to 1000 via the contacts array. It does not name alternatives or exclusions, but the usage context is clear.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.