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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real context beyond that: exact factors from official sources, and a concrete picture of the return payload (exact result, rounded display value, factor, plus extras like feet-and-inches, 1/16 inch fractions, pounds-and-ounces). It does not mention error behavior for mismatched categories.

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?

Purpose, factors and return shape are front-loaded in the first two sentences. The trailing unit-id block is long and largely duplicates the schema enums, but its category grouping earns its place by encoding valid pairing constraints; only mild redundancy remains.

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 no output schema, the description carries the return-value burden and does so concretely (exact value, formatted value, factor, extras). Inputs are fully enumerated and grouped. Missing only edge-case behavior such as cross-category inputs or out-of-range significant_digits handling.

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% (baseline 3), and the description goes beyond it by grouping the flat enum of unit ids into named categories (length, mass, temp, volume, area, speed, fuel, pressure, energy, power, data), which is the information an agent needs to pick a valid from/to pair. This is value the schema does not convey on its own.

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 (convert units) and immediately scopes it with distinguishing detail: official exact factors (NIST), Japanese traditional units, temperature and fuel economy. No sibling tool does unit conversion, so the agent can select this unambiguously.

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 implied by the domain rather than stated; there are no explicit when-to-use/when-not statements or references to alternatives (none exist among the date/tax/text siblings). The description does imply the from/to must share a category by grouping unit ids by category, which is helpful implied guidance, but it never says what happens on a cross-category pair.

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