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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so the write-to-external-party profile is known. On top of that the description adds genuinely useful semantics: the reply_token is private, a closed thread blocks sending, and a message is explicitly NOT a booking/order/payment confirmation. Delivery mechanics and any response payload remain undisclosed, which keeps it below a 5.

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 action and its required inputs, followed by constraints and the non-confirmation caveat. No filler; each sentence carries a distinct rule the agent could otherwise get wrong.

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 three-required-param outbound-send tool with no output schema, the description covers inputs, the closed-thread failure mode, and the contractual caveat. It stops short of describing what a successful call returns or what to do on token rejection, which is the remaining gap.

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 0%, so the description carries the parameter burden. It usefully explains the provenance of inquiry_id and reply_token (from contact_business, token private) and gives content guidance for message, but says nothing about the 500-character ceiling, message formatting, or what happens if the token is stale — one of three params is only loosely covered.

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 states a specific verb and resource — continue a conversation started by contact_business — and immediately distinguishes itself from that sibling by naming the inquiry_id/reply_token pair it consumes. An agent can tell this is a reply-to-existing-thread tool, not a new-request tool, without opening the schema.

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?

Explicit when and when-not guidance: send only what the customer asks, do not create a new initial request for a follow-up, and a closed conversation requires a new request (routing back to contact_business). Both the positive path and the excluded path are named.

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