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

Annotations already mark this as read-only, and the description adds important behavioral nuance: an empty about or picture means the peer has not shared it, not that it doesn't exist. This is valuable beyond the annotation and helps the agent interpret results correctly. It does not contradict the readOnlyHint.

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 two sentences, front-loaded with the purpose, and includes only essential clarifications. Every sentence earns its place, with no redundant wording or filler.

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 output schema exists, the description doesn't need to restate return values. It covers the key behavioral aspect (empty field interpretation), which is critical for correct use. For a read-only lookup with simple parameters, nothing essential is missing.

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%—both phone and account_id have descriptive entries in the schema. The description adds no additional parameter-level detail beyond what the schema provides, so a baseline score of 3 is appropriate. The mention of 'from one of your accounts' aligns with account_id but doesn't add new semantics.

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 ('look up') and a clear resource ('who a phone number is on WhatsApp'), enumerating the exact data returned (registration status, name, about, picture, and business details). It clearly distinguishes itself from sibling tools like wa_get_chat or wa_get_media by focusing on profile lookup.

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 clearly implies when to use this tool (when you need profile information for a phone number from one of your accounts). It does not explicitly mention alternatives or exclusions, but the purpose is unambiguous enough that an agent can select it without confusion among the many sibling operations.

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