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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safe-read profile is covered. The description adds value beyond that by naming the estimation algorithm (Carroll formula) and the output unit (kg), which tells the agent the result is an approximation method rather than a measured value.

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?

Four short, front-loaded sentences; the core purpose, use case, inputs, and output are stated with no filler. The trailing bundle reference is a minor add but still relevant.

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?

With an output schema present, the return value need not be spelled out, and the description still notes 'Returns weight kg'. For a two-parameter, fully-covered, read-only calculator this is essentially complete; only the usage exclusion 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 100% and both parameters are already documented with names. The description merely restates 'heart girth cm, body length cm' without adding format, range, or measurement guidance, so it earns the baseline 3 for a fully-covered schema.

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+resource ('Estimate horse weight'), the exact method (Carroll formula), and the driving inputs (heart girth and body length). This is unambiguous against the huge family of sibling calculate_* tools.

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?

Gives a clear usage context ('Use for vets, feed dosing') and points to list_bundles for related 'animaux' calculators, so the agent knows the domain. It stops short of naming a when-not condition or a specific alternative calculator to use instead.

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