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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=true), and the description adds real behavioral detail beyond them: default values for sport and aggregation, automatic upper-casing, regex validation (^[A-Z_]+$), and the closed set of aggregation values. It still says nothing about output shape (e.g. whether values are watts), but for an annotated read tool this is solid.

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 tightly packed sentences: purpose and scope first, then defaults and constraints. No filler, no repetition of the tool name, and every clause carries information an agent needs to call the tool correctly.

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 read-only tool with no output schema and four simple parameters, the description covers purpose, scope, defaults, and validation. The remaining gaps are the relationship to the cycling-FTP and power-zone siblings and any note on unit or response shape, which are minor but would help selection.

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 50% (sport and aggregation have no schema descriptions), and the description compensates by supplying their defaults, the upper-casing rule, the validation regex, and the allowed aggregation values. Start/end semantics (YYYY-MM-DD UTC) live in the schema and are not duplicated, which is appropriate.

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 gives a specific verb+resource ('FTP history for a sport over a date range'), which is far more informative than the name alone and makes clear this is a read of a time-series metric. It does not, however, distinguish itself from siblings such as get_cycling_ftp or get_lactate_threshold, which an agent could plausibly pick instead.

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 states the required date range and the defaults for sport/aggregation, but never says when to prefer this tool over get_cycling_ftp, get_power_zones_for_sport, or get_lactate_threshold, nor what happens if the date range is unbounded. The agent must infer selection from the name.

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