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

Annotations already declare non-readOnly, openWorld and non-idempotent, but the description adds the crucial business consequence: a real message leaves the system and lands in the Spoke conversation record. It also discloses the SMS-enabled-number prerequisite and the human-confirmation gate. Remaining gaps are cost, per-message rate limits, and delivery failure behavior.

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?

Four short sentences, front-loaded with the write marker and the side effect, then prerequisites. The trailing "POST /conversationMessages" is transport detail an agent does not need and is the one element not earning its place.

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?

For a 9-parameter outbound-send tool with no output schema, the description covers the essential mental model: what physically happens, who sends, what must be confirmed, what infrastructure is required. It is nearly complete, missing only reply-routing and notification semantics that a caller must currently infer from the stub enum names in the schema.

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 78%, so the schema already explains `to`, `body`, `confirm`, and the fromNumber/fromUserEmail alternative. The description reinforces the group-MMS consequence of multiple recipients but says nothing about `routingAction`, `notificationMode` (which has no schema description at all), or `conversationName`. That leaves the two enum parameters unexplained in both places.

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?

Opens with an explicit verb+resource marker ("WRITE: send a real SMS") and states scope precisely: single number or group MMS, from a company number or a user's conversation number. No sibling tool does anything comparable, so the boundary is unambiguous from the first clause.

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?

"Confirm the recipient and text with the user first" and "Needs an SMS-enabled number" give concrete preconditions for invocation, which is more than most mutation tools offer. It stops short of saying when NOT to use it (e.g. internal-only notifications, unsolicited outreach), so it is clear context without exclusions.

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