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

readOnlyHint=true already covers the safety profile, and the description adds genuinely new behavioral scope: which unit categories are supported and that unit names are accepted in Chinese or English ('公里、kg、°C、GB'). It does not describe the return payload or how ambiguous units are resolved, which is a minor remaining gap for a pure read.

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?

Three short sentences, front-loaded with the domain list and immediately followed by the trigger conditions and a canonical example. No redundant restatement of the title or schema.

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 3-required-param read-only converter this is essentially complete: scope, triggers, accepted input units, and a sample call. Without an output schema, a note on the returned value (numeric result, unit label, rounding) would make it fully self-contained.

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% and the schema already documents value/from/to with the same Chinese-English unit examples, so the description adds little parameter meaning. The inline example payload {"value":100,"from":"km","to":"mi"} confirms shape but does not extend semantics; baseline 3 applies.

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 eight supported unit domains (length/weight/temperature/volume/speed/area/data). Enumerating those domains also implicitly routes currency work to the currency_convert sibling, so an agent can tell the two converters apart without opening either schema.

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 concrete trigger phrases ('多少公里等于多少英里/磅换算公斤/华氏度转摄氏度'), which clearly establishes when to reach for this tool. It stops short of naming currency_convert as the alternative for money, so the exclusion is only implied by the domain list.

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