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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is fully covered. The description adds the meaningful scope detail that it derives both max HR and moderate/vigorous zones from age plus optional measured rates, but says nothing about the formula choice or the resting-below-max constraint.

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?

A single front-loaded sentence that states the action, the primary output, and the inputs with no filler or redundancy. Nothing is wasted.

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?

An output schema exists, so return values need not be described, and annotations cover the safety profile. However, for a 4-parameter tool where the method enum and the relationship between resting and measuredMax drive the result, the description omits guidance an agent would need to invoke it optimally.

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 75%, below the high-coverage baseline, and the 'method' enum (220 vs tanaka) has no description in either schema or prose — a material choice for a heart-rate calculator that goes unexplained. The phrase 'optional measured rates' loosely gestures at resting/measuredMax but does not clarify their distinct roles.

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 (calculate) and concrete resources (adult maximum heart rate, moderate and vigorous target zones) plus the inputs (age, optional measured rates). It is easily distinguished from numeric siblings like bmi_calculator or one_rep_max_calculator, though it never explicitly names an alternative.

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 implied by the calculator framing — an agent infers it applies when a user wants HR training zones — but there is no explicit when-to-use, when-not-to-use, or pointer to related tools. Adequate but leaves routing to inference.

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