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

Annotations already declare readOnlyHint=true, indicating safety. The description adds value by detailing the formula (Karvonen), the reason for accuracy (resting HR), and the output (ranges per zone and training benefit), enhancing transparency beyond 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?

The description is two sentences with no wasted words. The first sentence states the action and method, the second explains the advantage and output. It is front-loaded and every sentence earns its place.

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?

The tool has moderate complexity (3 parameters, formula). No output schema, but the description states it returns 'los rangos de pulsaciones para cada zona y su beneficio de entrenamiento,' which adequately covers return values. Annotations provide readOnlyHint. No critical information missing.

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%, so the schema already documents all three parameters. The description does not add new parameter-specific details beyond the schema's existing descriptions, meeting the baseline of 3.

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 specifies the tool calculates the 5 customized heart rate zones using the Karvonen formula, which is more accurate than simple max heart rate percentage. This clearly distinguishes it from sibling calculator tools, as none are dedicated to heart rate zones.

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?

The description explains why to use this tool over simpler methods ('Más precisa que el simple % FCmáx porque tiene en cuenta la FC en reposo'), providing clear context for when it is appropriate. However, it does not explicitly state when not to use it or mention alternatives.

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