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

Annotations already cover the read-only, open-world profile, but the description adds real behavioral detail: the range branch is hard-coded to aggregation="weekly", so the agent knows it cannot request daily values across a range. That is a genuinely useful constraint beyond the structured fields.

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 sentences, front-loaded with the output shape and then the branching rule, with zero filler. Every clause carries actionable information.

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 does state what comes back (endurance score / weekly aggregates) and how the two modes differ, which is the core need. It omits whether the metric requires a subscription tier and what the returned fields/units look like, leaving a small 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?

Schema coverage is 100%, so the baseline is 3, but the description goes further by explaining that merely the presence of `enddate` switches the underlying endpoint and forces weekly aggregation — semantics the schema (two plain date strings) does not convey.

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 the resource (endurance score) and the two granularities it can return (single day vs. weekly aggregates), which clearly separates it from sibling metrics like get_hill_score, get_running_tolerance, or get_fitness_age_data. It doesn't name a sibling to route against, but the verb+resource+scope is unambiguous.

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?

Explicitly tells the agent how to select between the two modes: omit `enddate` for a single day, include it for a range. That is concrete conditional guidance rather than implied usage. It stops short of naming alternatives when the agent wants raw daily data over a range.

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