send_private_message

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

With no annotations, the description carries the full burden. It discloses the two behavioral modes, but the critical consequence – that passive replies bypass proactive-message rate limits – is buried in the msg_id schema description rather than the tool description, and failure modes (e.g., reply-window limits for proactive sends) are not disclosed at all.

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 tight sentences, front-loaded with purpose followed by mode selection and parameter provenance; the final sentence partly duplicates the schema's parameter descriptions, which is the only thing keeping it from a 5.

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 mutation tool with no annotations and no output schema, it covers the essentials: what it does, the two modes, and where required IDs come from. Missing rate-limit and delivery-failure context keeps it from being fully complete.

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 parameters are already well documented; the description only adds that user_openid and msg_id originate from fetch_messages/bot_info returns, which is useful provenance but largely redundant with the schema's own wording.

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 specific verb and resource ('向指定 QQ 用户发送单聊消息') and immediately distinguishes the two operating modes (passive reply vs. proactive push), which is the key thing separating this from sibling read tools fetch_messages/bot_info.

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 gives the condition that selects each mode: pass msg_id for a reply to a just-received message, omit it for scheduled/proactive pushes with examples (task completion, reminders). No explicit 'when not to use' or named alternative tool, so it falls short of a 5.

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