Get a contact

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

Annotations already cover safety (readOnly, idempotent, non-destructive), so the bar is lower; the description still adds real behavior: it returns the stored fields (saved name, profile name, username, picture id) and returns `not_found` for unsaved numbers. It does not mention auth requirements or rate limits, but for a read tool with full annotations this is solid.

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?

Two tight sentences with no filler; the resource identity is front-loaded and the sibling contrast is relegated to the follow-up clause. Dense but each clause earns its place.

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?

There is no output schema, so the description should hint at the return shape — it does so by enumerating the returned contact fields. Combined with the not-found failure mode, an agent has enough to call and interpret it, though a fuller return description would be ideal.

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 both parameters (accountId, contactId) are already fully documented, including the E.164 and `lid:` forms. The description restates the identifier forms without adding syntax or edge-case detail beyond the schema, so the baseline 3 applies.

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?

States a specific verb and resource ('One contact of an account's address book') plus the accepted identifier forms, and explicitly contrasts scope with the sibling lookup_contacts. An agent can distinguish this from lookup_contacts without opening either schema.

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?

Names the alternative (lookup_contacts) and the condition that selects it: a number not saved on the phone yields `not_found` here, while lookup_contacts queries WhatsApp for any number. That is an explicit when-not plus alternative.

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