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

With no annotations, the description carries the burden well: it discloses the default channel, the WhatsApp opt-in precondition with its 24-hour window, the silent-drop risk, and the 1-credit cost. It omits failure/error behavior for the SMS path and any rate limits or throughput notes.

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 compact sentences with no filler, front-loading the core action and default before the conditional WhatsApp caveat and the cost note.

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 cost, channel defaults, and the main precondition for a tool with no annotations and no output schema. It would be stronger if it said what a successful send returns (message id, delivery status) since no output schema exists to describe the response.

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%, including a full enum description for channel that already covers opt-in and silent dropping, so the schema does most of the work. The description's added nuance is limited to calling SMS 'reliable delivery'; baseline 3 is appropriate.

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) and resource (SMS/WhatsApp messages), and the channel scope is clear from the first sentence. It is inherently distinct from siblings like emails or tts, though it does not explicitly name any sibling to contrast against.

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?

Gives clear channel-selection guidance: SMS is the default and reliable, WhatsApp requires opt-in within 24 hours. It does not mention when to prefer a sibling tool (e.g., emails) instead, but the when-to-use-each-channel guidance is explicit.

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