Look up contacts

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavioral context not in the structured fields: the 1-to-50 batching limit and the linked-device username-resolution limitation that will silently fail otherwise.

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 sentences, no filler, with the returned-fields summary front-loaded and the key limitation second. The opening clause is grammatically muddy ('About text ... asked from WhatsApp'), which slightly hurts readability, but nothing is wasted.

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, and the description compensates by naming the returned fields, which is the right move. Combined with 100% schema coverage and complete annotations, an agent has enough to call this correctly; only the relationship to overlapping siblings is left implicit.

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% and both parameters (accountId, contactIds) are fully documented in the schema, including the `lid:<digits>` syntax. The description restates the 1-to-50 range and the number/lid lookup form but adds no new parameter-level 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 states a specific verb (look up) and resource (contacts) and enumerates exactly which fields come back (about text, picture id, WhatsApp username, business name, device count), which goes well beyond the title. It also draws a boundary against one sibling by noting saved names live in list_contacts, though it never addresses get_contact, which overlaps in scope.

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 gives concrete invocation guidance: contacts must be resolved by number or `lid:` id, usernames cannot be searched because a linked device cannot resolve an @username, and it points to list_contacts for saved names. It stops short of saying when to prefer this over get_contact or check_numbers, so there is still inference left to the agent.

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