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

The annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, so the safety profile is fully covered. The description adds only that the data is '实时' (real-time) and that it returns major currencies, but it does not disclose which currencies count as '主流', whether the data is sourced externally or cached, or whether the real-time claim involves latency or rate limits.

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?

The description consists of two short sentences and is front-loaded with the core purpose. The trailing JSON example duplicates the schema's example, though that is a small redundancy rather than a distraction.

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?

There is no output schema, so the description must explain the return shape. It instead says only that it returns '主流币种汇率' (rates for major currencies), without saying whether these form a map keyed by currency code or which currencies are included, and it does not say whether the response includes the rate date.

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?

With a schema coverage of 100% on a single optional parameter, the schema already defines the base currency and its default, and it supplies the same example. Thanks to the example in the description, a caller can quickly see the call shape, but it largely repeats what the schema and its example already state, so it adds only marginal value.

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 clearly names a specific verb and resource: query real-time rates for major currencies against a base currency. It does not distinguish this tool from the sibling tool currency_convert, which also operates on currencies, so an agent must infer that this one fetches rates while the other one converts amounts between currencies.

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?

The description gives no guidance on when to use this tool rather than currency_convert, which is present in the sibling list, and it states no prerequisites or exclusions. It also does not say whether the tool should be used when a live conversion is needed or only when the raw rate is needed.

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