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

Annotations only declare readOnlyHint=false; the description supplies the substantive behavior: a hidden reserve price can immediately lock a binding deal, failure returns accepted=false plus a deal id, and there is a hard rate limit of 30 offers per item per 24 hours. It also discloses that offers are visible to the seller's AI and that a message body can be attached — well beyond what the single annotation conveys.

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?

Three dense sentences ordered by importance: what it does, what the result means, then the operational limit. Every clause carries information an agent needs — there is no filler or restatement of the title.

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 mutating, 6-parameter tool with no output schema, the description covers outcome semantics, the negotiation loop, and rate limits, which is nearly everything needed to call it correctly. It stops short of explaining what a lock commits the caller to (payment/next steps) and why idempotency_key should be reused on retries.

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?

At 67% schema coverage, baseline would be 3, but the description adds real meaning to the undocumented `price` (it is compared against the seller's hidden reserve and decides whether the deal locks) and confirms `body` as the optional message to the counterparty. It says nothing about `contact` or `idempotency_key`, which are left to their schema descriptions.

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 concrete verb+resource (向賣家的 AI 出價並開始議價) and its scope: it initiates a negotiation, not continues one. It names the sibling it is not (counter_offer) and describes the two possible terminal states (lock on reserve met vs accepted=false), so the agent can place it precisely among the deal tools.

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?

Explicitly routes the follow-up case to counter_offer ('之後等對方回應再用 counter_offer 還價'), which is the main sibling decision this tool creates. It does not however contrast with buy_listing (paying the asking price outright) or state prerequisites such as needing an authenticated account, so the when-not guidance is partial.

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