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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the read-only nature is covered. The description adds valuable behavioral context beyond annotations: results are ordered newest first and free accounts are limited to 3 days of data. This helps the agent set expectations and avoids surprises.

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: the first states the action, scope, examples, and ordering; the second adds a key constraint (free account limit). There is no redundancy or filler. The information is front-loaded in order of importance.

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?

The description covers what the tool lists, ordering, and a free-tier limit, and the output schema handles return values. However, the only parameter (days) is left unexplained, which is a clear gap for an agent trying to invoke it correctly. Given that there is only one parameter, this omission is more noticeable, so completeness is only adequate.

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 schema has one optional parameter 'days' with default 14 and zero description coverage. The tool description does not explain what 'days' means—whether it's the number of days to return, a look-back window, or something else. Since the description is the only place to explain this parameter, its omission is a significant gap, leaving the agent to guess its semantics.

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 clearly states the action (list), the resource (user's latest daily metrics), and provides concrete examples (sleep, HRV, stress) along with ordering (newest first). This distinguishes it from sibling tools like list_custom_metrics, which target custom metrics, and get_activity, which is about a single activity.

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 clear context for when to use the tool: when the user needs their daily health metrics. It does not explicitly contrast with alternatives or state exclusions, but the examples and focus on 'daily metrics' make the use case obvious. No misleading guidance is present.

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