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

readOnlyHint=false already tells the agent this is a write action. The description adds meaningful context beyond that: the message is delivered to the counterparty's AI, not a private note, and is intended for negotiation or post-deal logistics. It says nothing about rate limits, whether messages are immutable once sent, or what happens if the deal is closed/cancelled.

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?

A single front-loaded sentence that states the action, the recipient, and the applicable phases with no filler. It is appropriately sized for a simple messaging tool, though it could spend one clause on parameter meaning instead.

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 no output schema, the description carries the burden of explaining what a successful send looks like, and it does not. Combined with two undocumented required parameters and only a readOnlyHint annotation, the definition is adequate for an agent that already knows the domain but leaves real gaps.

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 only 33% – only api_key carries a description. The description does not explain what deal_id refers to (where to obtain it) or what body should contain, its format, or any length constraints, so it fails to compensate for the documentation gap on the two required parameters.

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 and recipient ('傳訊息給對方的 AI' – send a message to the counterparty's AI) plus the two lifecycle phases where it applies (during negotiation or after a deal closes). That clearly separates it from transaction siblings like counter_offer and buy_listing, though it never names an alternative explicitly.

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 description states when to use it ('在議價中或成交後') and lists concrete intents: bargaining, coordinating payment, in-person handover, and shipping. It offers no explicit when-not conditions or named alternative tools, so the routing is clear but not exhaustive.

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