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

Annotations already declare readOnlyHint, non-destructive, and closed-world. The description goes well beyond them: zones are final resolved values ordered by rising intensity, grouped by stream, bounds are unit-converted, template_mode returns coach-scoped zone configurations with names, and zone targets remain portable and resolved per athlete server-side. This is rich behavioral context that an agent could not infer from annotations alone.

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?

The description is front-loaded with the core purpose, then progressively adds filtering and template-mode details. Every sentence is relevant, though the single dense paragraph is longer than strictly necessary—the final sentence on portability, while useful, could be trimmed without losing critical meaning.

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 3-parameter tool with no output schema, the description covers the return format, ordering, grouping, unit conversion, template-mode behavior, coach/athlete scoping, and portability rules. Combined with annotations that cover safety, an agent has everything needed to call it correctly.

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. The description adds meaningful constraints not present in the schema: `athlete` defaults to the caller's own zones, `template_mode` returns configurations rather than zones, requires `sport`, and must never be combined with `athlete`. These are important usage semantics that elevate it above the baseline.

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 states a specific verb and resource ('list intensity zones'), defines the scope (one person, yours or an athlete's), describes the return shape (numbered zones with min/max bounds, converted to declared unit), and distinguishes it from siblings like list_sports and list_metrics. An agent can immediately tell what this tool does and what 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?

It explicitly prescribes when to use each mode: a bare call returns all zones grouped by stream, `sport` filters to one sport using a list_sports entry, and `template_mode=true` is reserved ONLY for authoring a reusable training_frame (coach-scoped, sport required, never combined with `athlete`). It also points to list_metrics for %-metric targets. No ambiguity remains.

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