Check WhatsApp numbers

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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds genuinely new operational context: the 10 calls-per-minute rate limit per key, the E.164 requirement, and the null result for local-format numbers. That is exactly the kind of behavior an agent cannot infer from structured fields.

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 short sentences, each carrying a distinct fact (purpose, format/edge case, rate limit), with purpose front-loaded. 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?

An output schema exists so return values need not be explained, and the description covers the remaining agent-critical facts: batch ceiling, input format, failure mode, and throughput limit.

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%; the numbers array has constraints but no prose. The description compensates by specifying the E.164 leading-+ format and the null outcome for local numbers, which is the key semantic an agent needs. gateway_id semantics are already covered by the schema description.

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 (check), resource (WhatsApp phone numbers), and a hard scope (up to 50, registration status) that cleanly separates it from the send_* siblings. An agent can identify it as the pre-send validation tool without opening the 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?

"before you send to them" gives an explicit usage context that ties it to send_message/send_batch. No named alternatives or when-not conditions are given, so it falls short of a 5.

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