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

Annotations already convey read-only and non-destructive behavior. The description adds valuable context beyond that by explaining that a name-based lookup may return a compact list if multiple people match, which is exactly the kind of behavioral nuance an agent needs. It does not contradict the annotations.

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?

Three sentences with no wasted words. It opens with the primary purpose, then explains parameter usage, and closes with a clear sibling-tool pointer—all front-loaded and well-structured.

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 tool with an output schema and rich annotations, the description is fully sufficient. It covers purpose, usage alternatives, multi-match behavior, and sibling differentiation, leaving no significant gaps.

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 100%, but the description enriches the parameters by explaining that name is a one-step path and contact_id is an exact identifier from list_contacts/search_contacts. It also reinforces the either/or relationship between the parameters, adding meaning beyond the schema.

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 it retrieves a contact from the Mac's Contacts.app by name or ID, which is a specific verb+resource. It also distinguishes itself from m365_get_contact and indicates there is no need to call search_contacts first, making its purpose unambiguous.

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 explicitly tells when to use this tool (local Mac contacts) and when not to (use m365_get_contact for Microsoft 365). It also explains the two usage modes (name for direct lookup, contact_id for exact lookup) and reassures the agent that prior search is unnecessary.

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