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

No annotations are provided, so the description carries the full burden. It does disclose that authentication is required, which is useful behavioral context. Yet it does not state whether the operation is read-only, what happens if the domain has no contacts, or any error/return behavior.

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 compact two-sentence definition, front-loading the action and scope, then adding authentication and the required parameter. No redundant or filler language.

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 simple read-only getter with two parameters and no output schema, the description covers the core purpose, authentication requirement, and required domain argument. It could be more complete with explicit alternative guidance or return-shape hints, but the essential information for invoking the tool is present.

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?

The description compensates for the missing domain parameter description by providing an example ('example.com') and clarifying that the contacts are 'assigned to a domain.' The sessionKey parameter is already fully described in the schema, so the combined coverage is adequate.

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 uses a specific verb ('Get') and resource ('contacts assigned to a domain'), and enumerates role types (registrant, admin, tech, billing). This clearly distinguishes it from sibling tools like getContact (single contact) or listContacts (by filtering context).

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 implies when to use it: whenever you need all contact roles for a specific domain. However, it does not explicitly mention when not to use it or point to alternatives like listContacts or getContact, so the agent is left to infer the boundary from the domain-specific wording.

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