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

Annotations already declare a safe, read-only, idempotent operation, so the bar is lower; the description still adds that output spans 'every common unit' rather than echoing the input unit. It does not describe the return shape (a table of converted values) or confirm rounding/precision, which leaves a modest gap for a tool with no output schema.

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, front-loaded with the capability and its purpose, followed by the two examples that resolve the only genuinely ambiguous part of the call. No filler or repetition of annotation-covered facts.

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 five-parameter, no-output-schema tool, the definition covers purpose, unit coverage and compound-input handling, which is enough for correct invocation; it never mentions the locale parameter's existence or that output enumerates all units, though the schema carries both adequately.

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 100%, so the baseline is 3, but the worked examples ('7 lb 4 oz' -> value 7, unit lb, extra 4) add genuine meaning beyond the schema's prose by showing exactly how compound imperial quantities map onto the value/unit/extra triple. The locale parameter's clinical-safety rationale is left to the schema, but that is already well covered there.

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 opens with a specific verb and resource ('Converts a weight ... or a length ... to every common unit') and enumerates the supported unit families, so it is immediately distinguishable from the growth/percentile siblings. It even states the downstream motivation (getting measurements into growth tools that take kg and cm), which no sibling does.

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?

It clearly states the triggering context: a measurement quoted in '7 lb 4 oz' or '2 ft 3 in' needs to be fed into growth tools that accept kg and cm. That is strong when-to-use guidance, but it stops short of naming which specific sibling to call next or any explicit when-not-to-use condition.

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