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

Annotations already establish readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely useful behavior beyond that: the result is truncated, capped at maxchart/maxpoly points, with explicit defaults of 2000 and 4000, which tells the agent data may be downsampled. It stops short of stating auth needs or what happens on invalid ids.

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 tight sentences with no filler, and the payload description leads. Structure is efficient but slightly note-like, opening with a bare noun phrase rather than an action, which mildly hurts scanability.

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 must sketch the return shape; it does say time series plus GPS track and warns about capping, which is the minimum an agent needs. It omits response format details (point units, ordering, what a capped result looks like) and any routing versus sibling activity tools.

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 only 33% (just activityId as 'Numeric id'), so the description carries the two undocumented params and does so well: it defines maxchart/maxpoly as point caps, gives their default values, and even maps the camelCase wire names maxChartSize/maxPolylineSize. It does not specify units or valid ranges, keeping it out of 5 territory.

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 phrase 'An activity's time series and GPS track' names a specific resource and payload, but supplies no verb, so the operation (retrieve) is only inferred. It also does not distinguish itself from close siblings like get_activity, get_activity_splits, or get_activity_hr_in_timezones, leaving the agent to guess which activity-data view it returns.

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?

There is no when-to-use statement, no prerequisite (e.g. that activityId must come from get_activities), and no mention of alternatives among the many get_activity_* siblings. Usage is only implied by the resource being described.

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