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

With no annotations, the description carries the full burden and does disclose meaningful traits: the template must be pre-approved, the no-24-hour-window behavior, and the billing model (billed like POST /v1/messages). It does not cover failure modes (e.g., unapproved template, invalid recipient) or auth requirements, which keeps it from a 5.

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?

Three tight sentences, each carrying distinct information (action/identity, timing rule, billing), with the core action front-loaded and no 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?

Covers the send semantics, approval prerequisite, timing, and cost, which is most of what an agent needs. With no output schema, it doesn't indicate what a successful send returns (e.g., a message id usable with get_message_status), leaving a small gap.

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 all five parameters (including E.164 format, language default, variable ordering, and default phone_number_id) are already documented in the schema. The description adds no parameter-level detail beyond that, matching the baseline of 3.

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 (Send) plus resource (approved WhatsApp template message) and the sending identity (connected WhatsApp Business number). It implicitly separates itself from send_sms/send_otp via 'WhatsApp template', but never names an alternative sibling explicitly, so it stops short of full sibling differentiation.

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 'templates may open a conversation at any time (no 24-hour window)' note implies the scenario where a template is needed versus a free-form session message, but the description never states when to prefer this over send_sms, send_otp, or send_bulk_sms. Usage is inferable rather than stated.

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