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

Annotations already declare readOnlyHint=true, so the safety profile is covered and the bar for the description is lower. The description's only extra signal is that it returns 'summaries' (aggregated, not raw samples) and maps to GET /v2/summary/activity/{user_id}; it says nothing about pagination, aggregation granularity, units, or return shape. With annotations carrying safety, this modest addition lands at a 3.

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 short sentences, front-loaded with the purpose. The endpoint-mapping sentence is lower value but compact and does not obscure the lead. No wasted padding.

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 tool with no output schema and fully documented parameters, the description covers the essentials but leaves the return payload unexplained — notably what an 'activity summary' contains and its time granularity. Adequate, with a clear gap around what comes back.

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%, so user_id, start_date, end_date, and provider are all documented in the schema (inclusive semantics, default-to-today, provider slug examples). The description adds no parameter detail beyond repeating 'user' and 'date range', so 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 ('Get activity summaries') plus scope ('for a user over a date range'), which is enough to separate it from siblings like vital_get_sleep, vital_get_body, or vital_get_workouts. It does not, however, explicitly contrast itself with adjacent retrievers such as vital_get_timeseries, so sibling differentiation is only implicit.

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 date-range phrasing implies the general usage context but there is no explicit when-to-use, when-not-to-use, or alternative named among the many vital_get_* siblings. An agent must infer on its own whether activity data belongs here or in vital_get_timeseries or vital_get_workouts.

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