get_activity_hr_in_timezones

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds only that the result is a per-zone time breakdown, with nothing about whether an activity lacking HR zones returns empty, errors, or a default zone set. That is modest added value against an already-covered read operation.

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?

One short sentence with zero filler, and the payload (per-zone time) is front-loaded. It is a noun fragment rather than a complete statement, which slightly reduces its structural clarity.

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 simple read with one documented parameter and no output schema, the description is close to complete about what comes back. It is still missing selection guidance against the several sibling heart-rate and zone tools, which is the main gap.

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?

With a single parameter and 100% schema description coverage, the schema fully documents activityId, so the baseline is 3. The description neither names the parameter nor adds accepted id forms or per-activity constraints beyond what the schema states.

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 names a specific resource (time spent per heart-rate zone) and is distinguishable from neighbors like get_activity_power_in_timezones or get_heart_rate_zones. It stops short of a verb+scope framing and never contrasts itself with the closest siblings, so it lands just under a 5.

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 guidance at all: no mention that this is per-activity and requires an activityId, and no pointer to get_heart_rate_zones or get_activity_power_in_timezones as alternatives. The agent must infer the use case from the name alone.

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