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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. Beyond that, the description adds a cost/performance cue ('cheap to ask') and, importantly, the return shape `{ unread }` in the absence of an output schema.

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?

Three short, front-loaded sentences with no filler; the return shape is stated up front. Slightly fragmentary phrasing keeps it just short of ideal, but nothing is wasted.

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 counter with no output schema, the description supplies everything an agent needs: what is counted and the exact response field. Only an explicit pointer to the list/mark siblings would make it fully complete.

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 tool takes zero parameters, so the baseline is 4 and there is nothing further the description could clarify about inputs.

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 the specific resource and quantity counted ('How many notifications are waiting'), making the operation unambiguous. It does not name a sibling such as list_notifications or mark_notifications_read, so differentiation is implied through 'One number' rather than stated.

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?

'One number, cheap to ask' implicitly signals this is the lightweight alternative to fetching the full notification list, which is useful routing guidance. However, no explicit when-to-use versus list_notifications/mark_notifications_read is given, so the agent must infer it.

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