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

Annotations already declare readOnlyHint=true, so the safety profile is covered; the description adds genuine context beyond that with the hard API cap of 100 messages and the oldest-first ordering. The remaining gap is that it says nothing about the return shape or pagination behavior.

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 sentences, zero waste; the core capability and ordering come first, with the API limitation as a supporting constraint. Every sentence earns its place.

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 read-only, three-parameter tool with no output schema, the description covers scope, ordering, limit, and the critical 100-message ceiling. It could still say what a returned message contains (id, body, sender, timestamp), which is the one meaningful omission.

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% and the schema already documents limit (1-100, default 30), account, and room_id. The description restates the limit default and framing but adds no new syntax or format detail, so the baseline 3 applies.

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 one Chatwork room's latest messages') plus ordering and default limit, which is far more than a restatement of the name. It does not explicitly distinguish itself from siblings like read_chat or search_chatwork_messages, so it falls short of a 5.

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 gives a real constraint (Chatwork exposes only the latest 100 messages, older history is unreadable), which indirectly tells the agent when this tool is insufficient. However, it never names an alternative such as search_chatwork_messages for older history or list_chatwork_rooms for obtaining room_id, so usage is only implied.

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