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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description adds genuinely new information — the per-call cost of 1 credit and the supported unit families — but says nothing about output precision, rounding, or error behavior for incompatible units.

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 compact fragments, capability list front-loaded with the cost note at the end — nothing is wasted. Minor deduction because "volume (UK and US)" is the only category given a qualifier, which reads unevenly and hints at an ambiguity that is never resolved.

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 three-parameter, non-destructive conversion utility with no output schema, the description covers scope and cost but leaves the return format (bare number vs value-with-unit) and unit-string conventions unexplained. Adequate to select the tool, thinner on how to invoke it correctly on the first try.

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 schema documents all three parameters, which sets the baseline at 3. The description adds no meaning beyond that — it never clarifies the expected unit string format (e.g. "km" vs "kilometres") or that value accepts both numbers and numeric strings, which is the main ambiguity an agent would face.

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 ("Convert") plus the full set of supported measurement families, which makes the scope concrete and implicitly separates it from the sibling convert_time and from calculate. It stops short of naming an alternative explicitly, so it lands at 4 rather than 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 only implied by the category list: an agent can infer this is the tool for physical-unit conversion and that convert_time handles time. There is no explicit statement of when to prefer this over calculate or convert_time, and no note on what happens with unsupported or mismatched units.

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