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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so safety is covered. The description adds real behavioral context beyond them: the output contents, the explicit limitation that no clinical expectation is expressed, and the grams-not-kilograms input convention that commonly causes wrong calls.

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?

Front-loaded with the definition, then triggers, then the scope caveat, then the unit warning. Four sentences, each carrying distinct information, with no filler or restatement of the title.

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?

There is no output schema, and the description compensates by enumerating the return contents (gram delta, percent delta, regained-birth-weight flag). Combined with full schema coverage for the four parameters, an agent has everything needed to call and interpret this tool correctly.

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 baseline is 3. The description goes beyond the schema by flagging the exact unit failure mode ('Grams only: 3400, not 3.4'), which is the highest-risk ambiguity for the two required numeric weights, and it defines what the echoed ageDays means implicitly via the later-weight framing.

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 computation on a specific resource: the delta between current and birth weight in grams and percent, plus whether birth weight has been regained. It is clearly distinguishable from siblings like growth_trend, growth_velocity, and ponderal_index, which track change over time or normalize by length rather than comparing two weights.

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?

Three concrete user-phrasing examples ('how much weight has my newborn lost', 'newborn weight loss percentage', 'has my baby regained birth weight') map directly to invocation triggers. It also bounds scope by stating it is arithmetic and does not judge whether the change is expected, though it names no alternative sibling for the clinical-interpretation case.

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