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

Annotations already declare a safe read (readOnlyHint=true, destructiveHint=false, closed-world), and the description adds substantial context beyond them: results are pre-filtered to charts the athlete actually has data for, with concrete examples (a tag breakdown only appears when tags exist, zones_duration_<stream> only when a slice exists). It also enumerates the meaningful dimension and measure values, which is exactly the behavioral shape an agent needs.

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?

Front-loaded with the one-line purpose, followed by structured detail on entry fields, filtering rules, and the athlete parameter. Slightly dense in the filtering sentence, but no sentence is filler.

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?

An output schema exists, so return structure needn't be restated, and the description still explains the semantics of the returned fields (chart/dimension/measure) that the schema likely does not. Combined with annotation-covered safety and full parameter coverage, nothing an agent needs to call this correctly is missing.

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 0% for the single `athlete` parameter, but the description compensates fully: it specifies the expected 'usr_…' handle format for a managed athlete and that omitting it targets yourself. That closes the documentation gap the schema leaves entirely open.

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?

Names a specific verb and resource ('List the statistics breakdowns available for an athlete') and anchors it with the concrete page reference (/statistic charts). It immediately contrasts with the sibling that consumes its output (get_stats_chart), so an agent can distinguish the discovery step from the retrieval step.

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 states that each entry's `chart` id is meant to be passed to get_stats_chart, which establishes the two-step workflow and the alternative tool. It also explains the filtering condition (only charts the athlete has data for) and the self-vs-managed-athlete case, though it does not state outright when NOT to call it.

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