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

Annotations already declare the full safety profile (readOnly, idempotent, non-destructive, closed-world), so the description only needs to add context. It does disclose that six speed-range zones are produced, but the 'Returns: {vma_kmh}' line is ambiguous and does not add meaningful behavior 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?

Two short sentences, front-loaded with the core purpose, with no filler. The trailing 'Returns: {vma_kmh}' fragment is redundant given a dedicated output schema and slightly muddles the otherwise clean structure.

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 single-parameter calculator with an output schema covering the return payload, the description gives enough to invoke correctly. It omits any note on the meaning of the zones or VMA validity, which are minor gaps given the schema and output contract carry the rest.

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 100% and the single vma parameter is fully documented with units and a range, so the baseline is 3. The description references VMA as the input basis but adds no format or interpretation detail beyond what the schema already provides.

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 and resource ('Calculate 6 running training zones as speed ranges based on VMA') and quantifies the output, which separates it from sibling calculators that produce different zone counts or metrics. It does not explicitly name the nearest sibling (calculate_heart_rate_zones) to draw the contrast, so it stops short of a 5.

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?

Usage is only implied through the required VMA input; there is no statement of when this tool is preferred over calculate_vma, calculate_vo2max or calculate_heart_rate_zones. The single pointer to 'list_bundles for related sport calculators' is a navigation aid rather than when-to-use guidance.

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