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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety and determinism need no description support. The description adds a mild behavioral fact — the result is a range derived from RDA-to-muscle-gain coefficients — but says nothing about output shape or how the level selection shifts the number. Acceptable but thin against an already-covered annotation set.

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 sentences plus a reference URL, with the core question ('How many grams of protein a day?') front-loaded so the purpose lands immediately. The trailing web-page link is the only element that is not strictly task-relevant, but it costs almost nothing.

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 low-complexity, zero-required-parameter calculator with a fully documented schema and no output schema, the description supplies enough to call it correctly: body weight plus an activity/goal level yields a daily range. Only the unit-handling nuance (kg vs lb vs units) is left entirely to the schema, which is a minor gap.

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 kg, lb, level and units are already documented in the schema, and the enums for level and units are self-explanatory. The description's 'activity or training goal' loosely maps to level but adds no format, unit-selection or default guidance beyond the schema. 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?

The description names a specific resource (daily protein intake in grams) and states the output form ('see your daily range for your body weight and activity or training goal'), so an agent knows it computes a protein target rather than a general calorie or macro figure. It does not name a competing sibling (e.g., macro_calculator, tdee_calculator) to sharpen the boundary, which keeps it 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 implied through 'for your body weight and activity or training goal' and the 0.8-2.2 g/kg framing, giving the agent a sense of when the tool applies. There is no explicit when-not or alternative-tool routing, so nothing tells the agent to prefer this over macro_calculator or bmi_calculator.

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