send_message

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

With annotations already declaring readOnlyHint=false, destructiveHint=true, and openWorldHint=true, the description adds real value by disclosing blocking semantics: it waits for Messages to confirm delivery and reports failure. That synchronous-confirmation behavior is not derivable from the annotations alone, and it usefully warns the agent that the call is not fire-and-forget.

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 tight sentences, front-loaded with the action and target, followed by the delivery-confirmation behavior. Nothing is wasted or 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?

There is no output schema, and the description compensates by explaining the return-relevant behavior (waits for delivery confirmation, reports failures). For a mutation tool whose safety profile is carried by annotations, this is nearly complete, though the irreversibility and confirm precondition are left to structured fields.

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 67%, and the 'to' formats (handle, email, chat GUID) are already documented in the schema, so the description largely restates it. 'text' and the semantics of 'confirm' are not illuminated beyond the schema text; baseline 3 is appropriate since the schema does most of the work.

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?

The description gives a specific verb+resource ('Send a message') and enumerates valid targets (phone number, email, chat GUID), which clearly distinguishes it from send_file and the read-oriented siblings. It does not explicitly name or contrast a sibling, but the action is unmistakable.

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?

There is no explicit when-to-use, when-not-to-use, or alternative guidance. An agent must infer that this is the tool for outbound text and that send_file covers attachments. The critical precondition (confirm must be true, only send when the user asked for this exact message) lives only in the schema, not the description.

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