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 covered. The description adds genuinely new context beyond that: the deterministic formula and the accuracy limitation implied by the medication-dosing prohibition.

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 dense sentence that front-loads the action, units, and formula, then immediately qualifies with the safety exclusion. No filler.

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 two-input pure calculation with no output schema, the description supplies method, units, and the output unit (pounds), and flags the one dangerous misuse case. Nothing an agent needs to invoke it correctly is 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 0%, so the description must carry units — and it does, specifying heart girth and body length are in inches, which is the critical ambiguity for both parameters. It stops short of describing measurement technique or plausible ranges, so not a full 5.

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 ('Estimate a horse's weight in pounds') and even gives the exact formula, so the computation is unambiguous. It is clearly distinguishable from the sibling pet calculators by species and method.

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?

Explicitly names the intended contexts ('records and nutrition discussions') and a hard exclusion ('never for medication dosing'), which is exactly the routing guidance an agent needs. It does not name a sibling alternative (e.g., a vet scale or a different tool), which keeps it just below a 5.

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