lookup_contact

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

With no annotations provided, the description carries the full burden and does well by disclosing key behaviors: it returns contact information or None if not found, explicitly resolves from macOS Contacts app, and includes error handling for access issues. It could improve by mentioning rate limits or permissions needed beyond access availability.

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 front-loaded with the core purpose, followed by concise details on behavior, parameters, and returns. Every sentence adds value with no redundancy, and it uses bullet points for clarity without unnecessary length.

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?

Given the tool's low complexity (1 parameter, no nested objects) and the presence of an output schema (implied by the Returns section), the description is complete. It covers purpose, usage, behavior, parameters, and return values adequately, leaving no significant gaps for the agent.

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 schema has 0% description coverage, so the description fully compensates by explaining the single parameter 'phone_or_email' as 'The phone number or email address to look up.' This adds clear meaning beyond the bare schema, making the parameter's purpose and format evident.

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 tool's purpose: 'Look up a contact by phone number or email address' with the specific verb 'look up' and resource 'contact'. It distinguishes itself from sibling tools like 'search_contacts' by focusing on exact lookup via identifier rather than broader search.

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 provides clear context for when to use this tool: to resolve contacts from the macOS Contacts app using a phone number or email. However, it does not explicitly state when not to use it or name alternatives like 'search_contacts' for broader searches, though the distinction is implied.

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