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

Annotations already declare readOnly/openWorld, so the description's value is in the extras it adds: the divergent return shapes, the underlying 2-GET vs 3-GET behavior, and the throw condition when startDate is missing. That is real behavioral context beyond the annotations.

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-loads the default behavior, then the two-branch distinction, then the return shapes. Dense but every clause (defaults, throw condition, GET counts) carries information. Slightly terse in phrasing but no wasted sentences.

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?

No output schema exists, yet the description details the exact return keys for both branches and the error case. Only minor gaps remain, such as endDate defaults and what aggregation actually changes in the output.

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% (latest and aggregation are undocumented in the schema), and the description compensates by giving the latest default, the aggregation='daily' default, and startDate's conditional requirement. This meaningfully fills the schema gap.

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 a specific verb+resource ('Lactate threshold: the latest values') and immediately distinguishes the two operating modes. An agent knows exactly what it fetches without opening the schema.

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 explains when each branch applies: latest=true is the default; latest=false returns history over a date range and requires startDate, otherwise it throws. No sibling alternatives are named, but the tool has no close sibling, so this is clear enough.

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