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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and closed-world, so the safety profile is fully covered without description help. The description adds the meaningful behavioral fact that a Karvonen variant exists and changes the calculation, but says nothing about input validation bounds or failure modes.

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, with the core capability front-loaded. The trailing 'See list_bundles for related sante calculators' is the weakest element and reads as filler for an agent trying to decide between this tool and its siblings, but it costs little.

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 2-parameter, single-responsibility calculator with a full output schema and complete annotations, the description covers what is computed and which zone family is returned. The omission is disambiguation from sibling heart-rate and training-zone tools, not missing operational detail.

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 both parameters carry their own descriptions, including the explicit 'Resting heart rate for Karvonen method (bpm)' on resting_hr. The description's mention of the Karvonen method merely restates that linkage, adding no format, default, or dependency detail beyond the schema, so the baseline 3 applies.

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 heart rate training zones Z1-Z5') and names the optional Karvonen method, so the agent knows exactly what is produced. It does not, however, distinguish itself from near-neighbors in the toolset such as calculate_training_zones_running or calculate_max_heart_rate, so an agent cannot route between them from the description alone.

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?

'Optionally using Karvonen method' implies the condition under which resting_hr is supplied, which is useful implied usage guidance. But no explicit when-to-use/when-not statement is given, and the only cross-reference points at list_bundles (a catalog tool) rather than at the competing sibling calculators, so alternative selection is left to inference.

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