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

Adds substantial context beyond readOnlyHint: a login requirement, that it inherits the session's audience permissions, that it returns null when no pin exists, and an explicit negative scope (no stream key, no signed playback URL). These are real behavioral facts an agent could not infer from the annotation, though it says nothing about who is allowed to pin or rate/consistency guarantees.

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 compact semicolon-delimited clauses, front-loaded with the precondition (login) and the core action, then permissions, then the empty case, then scope exclusions. No filler, though the string is dense and would read better split into two sentences with the null case made prominent.

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 two-parameter read-only fetch with no output schema, the description covers the essentials: auth prerequisite, permission inheritance, null-result semantics, and what is deliberately excluded from the response. No output schema means the return-shape caveat is genuinely necessary, and it is supplied.

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 must carry parameter meaning; it does map 'activity plus optional session' onto the two parameters, clarifying that the session argument is optional. However, it never explains that liveId is an alias of activityRef (a $ref to the same string type with only a length bound), which is exactly the ambiguity an agent would trip over.

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: read the currently pinned full question for an activity and optional session. The clause 'independent of recent chat history' (独立于最近聊天记录) actively separates it from read_messages / export_live_messages, and the 'full question' phrasing separates it from pin_live_message / hide_live_message, so an agent can route correctly without opening schemas.

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?

Gives clear selection context: use it when you need the pinned item for a given activity/session, and it explicitly states the empty case (returns null if nothing is pinned). It does not name the sibling tools for setting or clearing a pin, so the when-not guidance is implied rather than explicit.

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