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

Annotations already declare destructiveHint=true and openWorldHint=true, so safety is covered; the description adds genuinely new behavior — asynchronous queuing, dependency on the gateway app fetching the queue, and the 160-character/1-SMS cost boundary. It stops short of saying the send is irreversible or what happens on gateway failure.

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, front-loaded with the action and mechanism, followed by one recommendation sentence. No filler; the only mild redundancy is repeating the short-text advice already present in the message parameter description.

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 async queue model well, and with no output schema the description needn't explain return values — but it never says what a successful call yields (queue id? confirmation?) or how failures surface, which matters for an asynchronous send that depends on a separate device.

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% with an example phone format already documented, so the baseline is 3. The description adds practical meaning beyond the schema: the 160-character single-SMS threshold and the advice to avoid accents and emojis.

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+resource (enqueue an SMS) and explains the delivery mechanism (the user's own Android phone acting as gateway, configured in Minha Conta → SMS pelo celular). The channel is unambiguous versus siblings like send_whatsapp_message or send_email, though no sibling is named explicitly.

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 real selection context: delivery happens only when the gateway app polls the queue, and it only reaches CELULAR numbers (an implicit exclusion for landlines). It also recommends short, unaccented text with at most one link, but does not state when to prefer a different channel.

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