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

Annotations already declare readOnlyHint=false, destructiveHint=true and openWorldHint=true. The description usefully adds non-obvious behavior: the visitor sees the message in the chat widget (or WhatsApp/Google Chat) and a 30-minute live chat session starts. It does not, however, explain the destructive aspect or whether the send is irreversible.

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, zero filler, and the core action plus its visible consequence are front-loaded before the approval caveat. Every clause earns 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?

With a full-schema parameter set, no output schema, and annotations covering the safety profile, the description is nearly sufficient. A note on irreversibility or delivery failure handling would fully close the gap for this side-effecting send operation.

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 description coverage is 100%, so the baseline is 3. The description adds only the disposition of 'message' (the visitor-facing reply text); the helpful note that visitor_id comes from list_inbox_threads lives in the schema, not the description, so no extra value is contributed here.

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 precise verb+resource+actor: 'Send a human agent reply to the visitor in an inbox thread.' It clearly differentiates from siblings like add_suggested_message or update_thread_status by naming the actual sending action and its recipient.

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?

The closing line 'Only send text the user has approved' gives a real usage constraint, but the description never routes the agent among alternatives (e.g., when to reply directly vs. queue a suggested message, or how this relates to update_thread_status). Usage is implied rather than compared against siblings.

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