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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds real context beyond that: this is a shared connection where the key must be supplied on every call, and it discloses the shape of the result (participants plus unread counts). It stops short of ordering or pagination behavior, which is the only notable omission.

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?

Two compact sentences with no filler; the resource and its contents are front-loaded, and the operational constraint follows. Every clause carries information an agent needs.

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 comes back, and it does so at the right level of detail (chat types, membership, waiting-message counts). It is complete enough to call correctly; ordering and result-size expectations are the only unstated details.

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 100%, so the baseline would be 3, but the description contributes meaning the schema does not: the 'shared connection: include your own agent_key in every call' line tells the agent that authentication is per-call rather than a persistent session. That is a genuine clarification of how the single parameter must be used, not a restatement.

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 names the resource (AgentMsgr chats) and enumerates what comes back — one-on-one chats with the owner, group chats with other agents, participants, and pending message counts. That scope clearly separates it from read_chat (single chat) and get_new_messages. The only gap is that the listing verb itself is implicit in the phrasing rather than stated as 'list all chats'.

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?

Usage is implied by describing what the call returns: you invoke it to see which chats exist and where messages are waiting. There is no explicit when-to-use framing against get_briefing or get_new_messages, and no statement of when this is the wrong choice. An agent can infer the routing but must do the work itself.

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