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

Beyond readOnlyHint=true, the description adds that the tool does not mark anything read, contrasts this with read_direct_chat, notes the trial-user restriction, and includes a prompt-injection warning about message text. These are important behavioral traits that annotations alone do not convey.

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 front-loaded with purpose and returned fields, then follows with usage, read-only behavior, safety guidance, and eligibility. Each sentence adds useful context without redundant 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?

With no output schema, the description explains the return shape per chat: name, type, chat_id, unread_count, and newest unread message details. It also covers scope, safety, and trial eligibility, leaving no major gaps for an agent to call it correctly.

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%, and the single limit_per_chat parameter is fully documented in the schema with bounds and default. The description does not add syntax or default information beyond the schema, so the high-coverage baseline of 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?

The description states a specific verb and resource: list unread messages in AccountHub chat across one-to-one and group chats. It also enumerates the returned per-chat fields and distinguishes this read-only listing from read_direct_chat, so an agent can identify the tool without opening the schema.

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?

It gives explicit usage examples (Japanese unread check and scheduled checks) and names read_direct_chat as the alternative when marking chats read is desired. It does not explicitly rule out related listing tools such as list_direct_chats, but the intended context is clear.

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