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

Annotations already declare destructiveHint=true and idempotentHint=true, so the description doesn't need to restate destruction. It does add genuinely new context: the `full_access` API key requirement, which the agent cannot infer from annotations. It still omits whether the deletion is permanent, whether the contact can be restored, and whether related sends/history are affected.

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 destructive action is front-loaded in the first sentence, and the auth and endpoint facts follow compactly. The `operationId` and parenthetical group name are of marginal value to an agent selecting a tool, but cost little.

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 2-parameter, no-output-schema tool with rich annotations, the definition covers the action, the auth gate, and the target endpoint. Only the outcome of deletion (permanence, side effects on related data) is missing, which is a modest gap for a destructive operation.

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 coverage is only 50% – `audience_id` has no description in the schema. The endpoint template clarifies that `id_or_email` is a path segment scoped by audience, which reinforces the email-encoding note, but the description adds no explicit meaning for `audience_id` beyond its position in the URL.

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?

Names a specific destructive verb and resource ('Delete a contact'), which is unambiguous against siblings like delete_audience or delete_suppression. However, it offers no explicit differentiation from those siblings beyond the resource noun in the name.

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?

The description never says when to delete versus when to use update_contact, or how this interacts with suppression lists or cancel_email. No when-not or prerequisites are given beyond the auth requirement.

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