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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds one genuine behavioral fact — that unit names are accepted in Chinese or English — but says nothing about error handling for unrecognized units or precision/rounding of results.

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?

One front-loaded sentence naming scope plus a compact example — efficient overall. The example slightly duplicates the schema's own examples array, which is minor redundancy rather than 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 simple 3-parameter read-only converter with full schema coverage, the description gives enough to invoke it correctly. The one meaningful omission is the boundary against currency conversion, which is a sibling rather than a parameter concern.

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 each parameter is already documented with examples (km, 公斤, °C, GB). The description's example call and the Chinese/English note largely restate what the schema provides, so baseline 3 is correct.

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 (unit conversion) and enumerates the supported unit families (length/weight/temperature/volume/speed/area/data volume), which is more than the title alone conveys. However it never says it is distinct from the sibling currency_convert, so an agent must infer that currency is out of scope.

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 listed unit categories; there is no explicit statement of when to use this over currency_convert, nor what happens for an unsupported unit. The nearest sibling is the one case where guidance was most needed.

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