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

Annotations already carry the safety profile (readOnlyHint=true, idempotentHint=true, destructiveHint=false), so the description only needs to add context beyond that — and it does: login is required, type=GROUP conversations are system-formed ice-breaker groups containing two users plus an official account, and unread is per-item rather than a global total. These are meaningful non-obvious behaviors, though ordering and pagination are not disclosed.

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?

The description is compact and front-loaded: login requirement and core purpose appear in the first sentence, followed by three cleanly labeled sections (【需要登录】【两种会话】【未读】). Every sentence earns its place — the GROUP vs DM distinction and the unread summation note are high-value domain context, not filler or restatement.

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 zero-parameter, read-only listing tool whose safety profile is fully covered by annotations, the description covers the essentials: what is returned, the two conversation types and their semantics, and downstream routing to read_messages / send_message / request_contact_exchange. With no output schema, the listed fields partially compensate; only ordering and pagination limits are left unstated, which is minor for the core 'list then pick a conversationId' workflow.

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?

The input schema has zero parameters, so the baseline is 4 and the description carries no obligation to document parameters. It instead adds value by clarifying output semantics (unread, latest preview, member info, title), which is the closest analog to parameter meaning for this tool. There is no parameter documentation gap to compensate for.

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: '列出当前用户的所有私信会话' (list all the current user's private message conversations), and enumerates what each item contains (unread, latest preview, member info). It also distinguishes it from downstream siblings by framing it as the entry point that yields conversationId for read_messages / send_message, and its GROUP type discussion separates it from get_conversation and mark_conversation_read.

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-to-use and workflow guidance: '先用它拿 conversationId 再 read_messages / send_message' tells the agent to call this first. It also gives an explicit exclusion — '别再去找什么「未读总数」工具' — and routes contact-exchange needs to request_contact_exchange in DM rather than GROUP, which is actionable alternative selection, not vague implication.

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