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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds the operational context that this is a pre-check, but it does not disclose additional behavioral traits such as return semantics, error behavior, or rate limits. This is adequate but not rich.

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, and the core purpose is front-loaded. Every part of the description earns its place, including the concrete formatting instruction for the phone number.

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?

The tool is a simple, read-only check with one required parameter and no output schema. 'Check whether' implies a boolean-style result, but the description does not explicitly confirm return behavior or how failures are signaled. Still, the essential calling context and parameter requirement are present, so it is nearly complete.

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 50%: phone_number has no schema description, and the description compensates by specifying it must be in international form. account_id already has a detailed schema description, so the tool description does not need to repeat it. This adds meaningful guidance beyond the bare 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 names a specific verb ('Check whether') and a clear resource ('a phone number corresponds to a WhatsApp user/account'), and it differentiates the tool by anchoring it to the pre-outreach and recipient-resolution use case. This makes the purpose easy to distinguish from related siblings like whatsapp_get_profile or messaging_resolve_recipient.

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 gives clear usage context: use it before starting outreach or resolving a WhatsApp recipient. It does not explicitly name alternatives or state when not to use it, so it falls short of a 5, but the intended trigger conditions are obvious.

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